Gas dispersion manufacture of nanoparticulates, and nanoparticulate-containing products and processing thereof
In one aspect, the present invention relates to a method of making multi-phase particles that include nanoparticulates and matrix, which maintains the nanoparticulates in a dispersed state. A flowing gas dispersion is generated that includes droplets of a precursor medium dispersed in a gas phase. The precursor medium contains liquid vehicle and at least a first precursor to a first material and a second precursor to a second material. The multi-phase particles are formed from the gas dispersion by removing at least a portion of the liquid vehicle from the droplets of precursor medium. The nanoparticulates in the multi-phase particles include the first material and the matrix in the multi-phase particles includes the second material.
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The present invention relates to nanoparticulate materials, products containing and made using nanoparticulate materials, and methods of making and processing nanoparticulate materials.
BACKGROUND OF THE INVENTIONNanoparticulate materials, and methods for making nanoparticulate materials, have been the subject of recent interest and research because of the advantages provided by nanoparticulate materials over larger sized particulate materials. One advantage of nanoparticulates is increased surface area, which is useful in a variety of applications, including catalyst, electrocatalyst, absorbent, chemical separations and bio-separation applications. Nanoparticulates are also useful in formulations of inks, pastes and tapes that are used in depositing thin or thick films, such as optically transparent conductors for use in displays, magnetic coatings for storage media and printed circuitry for electronic applications. Inks and pastes with nanoparticulates have improved rheology characteristics (e.g., flowability), which allow thinner layers to be applied and allow deposition of features with smaller dimensions. Lighting applications also benefit from the properties of nanoparticulate materials; for example, semiconductor nanoparticulates, in addition to other uses, are useful because of their “quantum dot effect,” which allows the luminescent color of a semiconductor nanoparticulate to be tailored according to the size of the nanoparticulate. In addition to the examples above, nanoparticulate materials are being used, or considered for use, in many other applications including pharmaceutical formulations, drug delivery applications, medial diagnostic aids, abrasives, pigments, phosphors for lighting, dental glasses, polymeric fillers, thermal interface materials and cosmetics.
As a result of the large number of applications for nanoparticulate materials, a variety of methods have been developed for making and processing nanoparticulates. One common problem faced by these methods is the tendency of the nanoparticulates to agglomerate because of their high surface area. Once the nanoparticulates have agglomerated, often they do not provide the same advantages achieved when the individual nanoparticulates are in a dispersed state. Consequently, the tendency of nanoparticulates to agglomerate makes the forming, processing, handling, transporting and use of nanoparticulates problematic. Complicating matters is that separating or redispersing nanoparticulates once they have agglomerated is difficult to do.
Thus, there is a need for additional methods of forming, processing, handling, transporting and using nanoparticulates and new nanoparticulate products that alleviate some or all of these problems.
SUMMARY OF THE INVENTIONWith the present invention, problems with agglomeration that may be encountered during manufacture, processing, handling and using nanoparticulates may be addressed through manufacture and/or processing of nanoparticulates in a dispersed state within multi-phase particles in which the nanoparticulates are maintained in the dispersed state by matrix.
A first aspect of the invention involves a method for making nanoparticulates, with the method including generating a flowing gas dispersion containing droplets of a precursor medium dispersed in a gas phase, removing liquid vehicle from the droplets of the gas dispersion, and forming the multi-phase particles. In one implementation of this first aspect, the multi-phase particles are formed in the gas dispersion under controlled conditions. In variation of this implementation, the controlled conditions include not permitting the average stream temperature of the gas dispersion to exceed a melting temperature for more than a short time, such as no longer than 10 seconds. In variation of this implementation, a reducing agent is used to promote formation of nanoparticulate material. In another implementation this aspect, first particles are formed in the gas phase and then the first particles are modified to form second particles that are in the multi-phase form including the nanoparticulates and the matrix. In one variation of this implementation, the conversion to the second particles occurs in the gas dispersion. In another variation of this implementation, the conversion to the second particles occurs after the first particles have been separated from the gas dispersion. In another implementation of this first aspect, the multi-phase particles are formed in the gas dispersion and collected from the gas dispersion directly into a liquid medium.
A second aspect of the invention involves processing of the multi-phase particles, or portions thereof. In one implementation of this second aspect, the processing involves decomposing the multi-phase particles in a liquid medium to release the nanoparticulates for dispersion in the liquid medium. In one variation of this implementation, the processing involves surface-modifying the nanoparticulates. In another variation of this implementation, the processing involves, after releasing the nanoparticulates, fixedly dispersing the nanoparticulates in a composite structure with a different matrix. In another implementation of this second aspect, the processing involves modifying at least one of the matrix and the nanoparticulates while the nanoparticulates remain in the dispersed state of the multi-phase particles. In one particular embodiment, a portion of the matrix is removed while retaining nanoparticulates in the dispersed state. In another implementation of this second aspect, multi-phase particles are subjected to treatment in a liquid medium. In one variation of this implementation, the solutes are removed from the liquid medium to reduce the concentration of the solutes in the liquid medium. In one variation of this implementation, the solutes are separated by passage through a membrane. This second aspect of the invention may be combined with the first aspect of the invention to make the multi-phase particles and then process the multi-phase particles, or portions thereof.
A third aspect of the invention involves particulate product comprising the multi-phase particles. In one implementation of this aspect, the multi-phase particles a portion of the matrix is selectively removable relative to another portion of the matrix. In one variation of this implementation, the matrix includes at least two different materials, with one being selectively removable relative to the other. In another implementation of this aspect, the multi-phase particles comprise nanoparticulates of at least two different compositions. In another implementation of this aspect, the multi-phase particles include a surface-modifying material, and the multi-phase particles are decomposable to release the nanoparticulates with surface modification of the nanoparticulates through association with the surface-modifying material. The first and/or second aspects of the invention are useful for making multi-phase particles of the third aspect of the invention.
These aspects, implementations and variations, and other aspects, implementations and variations of the inventions are discussed below.
BRIEF DESCRIPTION OF THE DRAWINGS
With reference to
During the generating gas dispersion 102, the precursor medium is processed to form the droplets of the gas dispersion produced during the generating gas dispersion 102. The precursor medium is a flowable medium containing a sufficient proportion of a liquid vehicle to impart flowability to the medium. In addition to the liquid vehicle, the precursor medium also includes one or more precursors. Each such precursor in the precursor medium is a material that contributes one, or more than one, component to the composition of the particles formed during the forming particles 104. Each precursor included in the precursor medium is either dissolved in the liquid vehicle or is in a fine particulate form suspended in a liquid vehicle. In addition to the precursor, the precursor medium may include one or more other additives, or reagents. As used in this context, reagent refers to a material included in the precursor medium for some purpose other than to provide a component for inclusion in the particles formed during the forming particles step 104.
The gas dispersion is in the nature of a mist or aerosol of the droplets in the gas phase. During the generating gas dispersion 102, the gas dispersion is prepared using any technique for atomizing the precursor medium (i.e., converting the precursor medium to the finely divided form of droplets) and dispersing and suspending the atomized droplets of precursor medium in a gas phase.
During the forming particles 104, liquid vehicle is removed from the droplets to the gas phase of the gas dispersion and particles are formed, which particles are dispersed in the gas dispersion. Removal of the liquid vehicle from the droplets may be accomplished, for example, by vaporizing the liquid vehicle, with liquid vehicle vapor mixing into the gas phase. Such vaporization is preferably aided by heating of the gas dispersion. Also during the forming particles 104, precursors in the gas dispersion may undergo any reactions or other transformations or modifications required to make the particles. The final particles resulting from the forming particles 104 may be formed while the particles remain dispersed in the gas from the forming particles 104 may be formed while the particles reunion dispersed in the gas dispersion or may be formed during further processing conducted after removal of particles from the gas dispersion. Processing that may occur during the forming particles 104 while particles remain dispersed in the gas dispersion and after removal of particles from the gas dispersion may include, for example, reaction of precursors, material phase redistribution, crystal growth or regrowth, nanoparticulate phase formation, growth of nanoparticulate domains (such as through nanoparticulate agglomeration or coalescence), compositional modification, particle coating, etc. For example, particles as formed in the gas dispersion may not have undergon all necessary chemical reactions for morphological modifications necessary to form the desired final particles. In this case, forming particles 104 might involve a step of collecting particles from the gas dispersion and a step of subjecting the collected particles to a subsequent heat treatment during which precursor reactions or other particle transformations or modifications may occur that are required to make the desired final particles. Also, all precursors and reagents required to form the desired final particles during the forming particles 104 may be included in the gas dispersion as generated during the generating gas dispersion 102, or one or more precursor or reagent may be introduced separately during the forming particles 104.
The final particles produced during and resulting from the forming particles 104 are multi-phase particles, meaning that at least two distinct material phases are present in the particles. Moreover, the multi-phase particles comprise the nanoparticulates that include at least a first material phase and the multi-phase particles also comprise the matrix that includes at least a second material phase that is different than the first material phase.
In the multi-phase particles 108 of
With reference to
As one example, the matrix may be wholly removable, or partially removable to a sufficient extent, to release the nanoparticulates for further processing or for use. In one variation of this example, the matrix may comprise only material(s) designed to be removed at the same time. In another variation of this example, the matrix may include a material that is selectively removable relative to another material to provide enhanced access to the nanoparticulates for intermediate processing prior to removal of other matrix material(s) to effect release of the nanoparticulates. As another example, all or part of the matrix may be designed for permanent use. In one variation of this other example, the matrix as originally formed during the forming particles 104 may be designed to permanently maintain the nanoparticulates in a fixed dispersion for some final application. In another variation of this other example, a portion of the matrix may be selectively removable relative to another portion of the matrix designed to be permanent, providing enhanced access to the nanoparticulates for purposes of intermediate processing prior to final use or for purposes of a final use.
A variety of specific examples will now be presented of materials for possible inclusion in nanoparticulates and matrix of multi-phase particles manufacturable using the method of the invention. It should be appreciated, however, that the examples are non-limiting in that other non-listed materials could additionally or instead be included in nanoparticulates and/or matrix. Also, although some preferred materials are listed for each of the nanoparticulates and the matrix, it should be understood that any of the exemplary materials identified for potential use in nanoparticulates could instead be used in matrix and any of the exemplary materials identified for potential use in matrix could instead be used in nanoparticulates.
With reference to
In one particular implementation of the invention, the nanoparticulates comprise phosphor materials for use in the nanoparticulates, such as when the nanoparticulates are to be used as phosphors in a display application. Phosphors are substances that are capable of luminescence. The luminescence involves emission of radiation in response to a stimulus or excitation. Preferred luminescence of phosphors for use with this implementation of the invention includes emission of visible light for use in display applications. Such phosphors may, for example, be cathodoluminescent, electroluminescent, photoluminescent or x-ray luminescent. For example, the phosphor materials may be organic or inorganic in composition, or may be a composite of inorganic and organic light emitting materials. Inorganic phosphor compositions typically include a host material and one or more dopants, also referred to as activator ions. Examples of host materials include yttrium oxides, yttrium oxysulfides, gadolinium oxysulfides, sulfides (such as for example zinc sulfide, calcium sulfide and strontium sulfide), silicates (such as for example zinc silicate and yttrium silicate, thiogallates (such as for example strontium thiogallate and calcium thiogallate), gallates (such as for example zinc gallate, calcium gallate and strontium gallate), aluminates (such as for example barium aluminate and barium magnesium aluminate (BAM)), thioaluminates (such as for example barium thioaluminate) and borates (such as for example yttrium-gadolinium borate). Table 1 lists some non-limiting examples of inorganic phosphor materials, including host material and exemplary activator ions, and the type of excitation for luminescence.
In one particular implementation of the invention, the nanoparticulates comprise catalyst compositions. Catalysts are substances that affect the rate of chemical reactions without themselves being consumed or undergoing chemical change. Nanoparticulate catalysts have an advantage of very large specific surface area, providing a large amount of catalytic surface area per unit mass of catalyst material. Catalysts may be organic compositions, or inorganic compositions, or a combination of organic and inorganic constituents. Preferred catalysts for use in nanoparticulates of the invention include inorganic catalytic material, which may be either supported or unsupported. By a supported catalyst, it is meant that the catalytic material is supported by a support material, which imparts structural integrity to the composition. The support material may or may not affect the catalytic performance of the composition. By unsupported catalyst, it is meant that the catalytic material itself imparts structural integrity to the composition. Unsupported catalysts are also referred to as being self-supporting. Catalyst compositions may include only one catalytic material or may include multiple different catalytic materials. Supported catalyst compositions may include only one type of support material or may include multiple different types of support materials. In addition to catalytic material, and optionally support material, catalyst compositions may also optionally include one or more than one additive, such as one or more than one promoter.
The catalysts may be of any composition. For example, the nanoparticulates could include an electrocatalyst material, some non-limiting examples of which include perovskite phase metal oxides (such as for example La1-xSrxFe0.6Co0.4O3 or La1-xCax CoO3); and oxygen deficient Co—Ni—O spinels of the form AB2O4 where A is selected from divalent metals such as Mg, Ca, Sr, Ba, Fe, Ru, Co, Ni, Cu, Pd, Pt, Eu, Sm, Sn, Zn, Cd, Hg or combinations thereof and B is selected from trivalent metals such as Co, Mn, Re, Al, Ga, In, Fe, Ru, Os, Cr, Mo, W, Y, Sc, lanthanide metals and combinations thereof. Other examples include catalyst materials for water-gas shift reactions, auto-thermal reforming, steam reforming and hydrodesulfurization processes, some non-limiting specific compositional examples of which are shown in Table 2. Table 2 lists both supported and unsupported (self-supporting) catalyst materials. In the compositions of Table 2, γ-alumina (γ-Al2O3), magnesia (MgO), silica (SiO2) and ceria (CeO2) function as support materials. In Table 2, the first column identifies the general catalyst formulation(s), the second column identifies a catalytic application in which a catalyst of that formulation might be used, the third column provides some examples of specific catalyst compositions, the fourth column summarizes exemplary reaction temperatures during use of the catalyst in the identified catalytic application, and the fifth column notes general variations in catalyst manufacture conditions (e.g., during the forming particles 104 step of
WGSR = water gas shift reaction
ATR = auto-thermal reforming
SR = steam reforming
LT = low temperature
HT = high temperature
HDS = hydrodesulfurization
In one implementation of the invention, the nanoparticulates comprise pigments. Table 3 lists some non-limiting examples of inorganic pigment materials and the color imparted by the material.
In one particular implementation of the present invention, the nanoparticulates comprise a combination of pigment materials. For example, the nanoparticulates may comprise a combination of two or more of the inorganic pigments listed in Table 3 in order to create a color that cannot be created with a single inorganic pigment. As another example, the nanoparticulates may contain an inorganic pigment, such as those listed in Table 3, combined with an organic pigment. A layer of organic pigment on an inorganic pigment may also aid dispersion of the pigment nanoparticulates into a polymer, organic liquid or other organic medium.
In one particular implementation of the invention, the nanoparticulates comprise semiconductor materials. Semiconductor materials in nanoparticulate form have a variety of uses including applications in solar cells and phosphors for diagnostic applications. Some examples of types of semiconductor materials include doped and undoped: IV semiconductors, II-IV semiconductors, II-VI semiconductors, III-V semiconductors and rare earth oxides. Specific non-limiting examples of semiconductor materials that may be used in the nanoparticulates include silcon alloys, germanium alloys, PbS, PbO, HgS, ZnS, CdSe, CdTe, CdS:Mn, InP, InN, Ge, Si, CeO2, CsO2, Eu2S3, EuO, ZnO, GaP, and GaN.
In one particular implementation of the invention, the nanoparticulates comprise a transparent electrical conducting material. Transparent electrical conductors are useful in a variety of applications, such as for example in manufacturing displays and in photovoltaic cells. Table 4 lists some non-limiting examples of transparent conducting metal oxides that may be included in the nanoparticulates.
It should be understood that the materials listed above are non-limiting examples of materials that may be included in the nanoparticulates, either as a sole material phase or as one of multiple material phases in the nanoparticulates. In other embodiments, the nanoparticulates may contain materials other than those previously noted that may be useful in a desired application of the nanoparticulates. For example, in chemical mechanical polishing applications the nanoparticulates may contain one or more hard materials such as metal oxides (e.g. silica, alumina, zirconia and ceria) carbides and nitrides. For absorbent applications, the nanoparticulates may contain compounds such as zinc oxide, magnesium oxide, barium oxide, calcium oxide, copper oxide, silver oxide, barium carbonate, nickel oxide, iron oxide, zirconium oxide, manganese oxide and lithium oxide. Other non-limiting examples of applications for materials included in the nanoparticulates include: anti-abrasive, electrochromic, thermochromic, electrically conductive, electrically resistive, dielectric, moisture absorbent, cosmetic, pharmaceutical and magnetic.
One particularly useful application for use of the nanoparticulates made using the present invention is in ink and paste formulations. Nanoparticulates provide a variety of advantages over larger particulates in ink and paste formulations such as higher solid loading, better flowability, an ability to deposit smaller features and ink stability (e.g., reduced tendency for particle settling). A variety of techniques are available for depositing, patterning and/or printing inks and pastes that contain nanoparticulates made using the present invention, some non-limiting examples of which include ink jet printing, lithographic printing, flexographic printing, roll printing, intaglio, spraying, dip coating, spin coating, stenciling, stamping, liquid embossing, gravure printing and screen printing.
The advantages achieved by using nanoparticulates in inks and pastes are particularly important in printing circuit features for display and electronic applications, manufacturing membrane electrode assemblies for use in fuel cells and manufacturing of batteries. Many circuit features, or components, of displays and electronics, such as conductors, dielectrics, light emitters and resistors are deposited onto substrates (organic and inorganic) using inks and pastes, which are applied to the substrates using a variety of techniques, such as those previously listed. Typically, after an ink or paste is deposited onto a substrate, the deposited paste or ink is subjected to heat treatment to convert the ink or paste into the desired circuit component. For example, one technique for making electrically conductive lines on circuit boards is by depositing an ink containing particles of electrically conductive material (such as particles of an electrically conductive metal, e.g., gold, silver, copper, nickel, conductive alloys) onto the circuit board substrate, such as by ink-jetting, and then heat treating the deposited ink to form a solid electrically conductive line. These inks typically contain metallic particles. Because of the smaller size, using nanoparticulates in the inks will allow the deposition of thinner conducting lines on substrates, and consequently, will allow a greater number of circuit features to be deposited per unit area of substrate (e.g., electrically conductive lines can be formed with a smaller pitch, or center-to-center spacing between the lines). Similarly, use of the nanoparticulates made using the present invention in inks for display applications will allow a greater number of features to be deposited per area of substrate.
Fabrication of membrane electrode assemblies (MEAs) for use in fuel cells can also benefit from the use of inks containing the nanoparticulates made using the present invention. For example, an ink containing carbon and/or catalyst nanoparticulates can be printed on a substrate of ion exchange membrane to form an electrocatalyst layer. Catalysts used in MEAs can be very expensive (e.g., platinum catalystic metal), and the ability to fabricate MEAs using nanoparticulate-sized catalyst particles can greatly reduce the cost of manufacturing MEAs. Additionally, increased surface area that may be provided by nanoparticulates can also contribute to improved performance of the MEAs.
As previously noted, by nanoparticulates it is generally meant particles with a weight average particles size of less than 500 nm, and typically in a range of from 1 nm to 500 nm, although a particular size or size range might be more preferred for some applications. One particular advantage of the method of the present invention is the ability to make nanoparticulates with a weight average particle size of from about 500 m to about 50 nm. Nonparticulates within this size range are difficult to make using other methods for making nanoparticulates, which other methods often tend toward production of smaller, and often much smaller, nanoparticulates.
Current methods other than that of the present invention often do not permit growth of the nanoparticulates to these larger nanoparticulate sizes. With the present invention, however, there is a significant ability to control nanoparticulate growth through use of the matrix structure. For example, smaller nanoparticulates are generally favored for production in the gas phase during the forming particles 104 (
For many applications, it is preferred to use nanoparticulates having a weight average particle size of generally larger than about 50 nm. One reason that nanoparticulates of this size are preferred for many applications is because it is easier to handle the larger nanoparticulates than the smaller nanoparticulates that are smaller than about 50 nm. One advantage of the method of the present invention is that it is often controllable to make nanoparticulates within a desired range. In one embodiment, the nanoparticulates in the multi-phase particles manufacturable using the method of the present invention have a weight average particle size in a range having in any combination a lower limit selected from the group consisting of 50 nm, 55 nm, 60 nm, 65 nm, 70 nm and 75 nm and an upper limit selected from the group consisting of 500 nm, 450 nm, 400 nm, 350 nm, 300 nm, 250 nm and 200 nm. In one particularly preferred embodiment, the nanoparticulates have a weight average particle size of from 70 nm to 300 nm.
The method of the present invention can also be used to make smaller-size nanoparticulates, which may be preferred for some applications. In one embodiment, the nanoparticulates in the multi-phase particles manufacturable using the method of the invention have a weight average particle size in a range having in any combination a lower limit selected from the group consisting of 1 nm, 10 nm, 20 nm and 30 nm and an upper limit selected from the group consisting of 150 nm, 100 nm, 75 nm and 50 nm.
In like manner to the description above concerning manufacture of larger-size nanoparticulates, the final size and other properties of these smaller-size nanoparticulates may result directly from the forming particles loy (
As noted previously, the matrix includes one material or a combination of two or more materials that function to maintain the nanoparticulates at least partially and preferably completely separated in a dispersed state in the particles. Examples of some general types of materials for possible inclusion in the matrix include salts, polymers, metals (including alloys and intermetallic compounds), ceramics and inorganic carbon (such as graphitic or diamond-like carbon).
In one particular implementation of the invention, the matrix comprises one or more than one salt material. Matrix salt materials are preferred, for example, for many applications when it is desired to have a matrix that is partially or wholly removable, because the salt material of the matrix can be selected to be dissolvable in a liquid medium that is not detrimental to the nanoparticulates. For water soluble salts, a convenient choice for the liquid medium is water or an aqueous solution, which may be neutral, basic or acidic depending upon the specific application and the specific matrix salt material to be dissolved. The matrix salt material may be an inorganic salt or an organic salt, with inorganic salts being generally more preferred. Table 5 lists some non-limiting examples of inorganic salts that may be used as a matrix material, along with some information concerning the inorganic salts.
In one particular implementation of the invention, the matrix comprises one or more than one polymer. It may be desirable to include a polymer material in the matrix for a variety of reasons. For example, a polymer may be selected for easy dissolution in a liquid medium to release the nanoparticulates for further processing or use. A polymer material that is soluble in an organic liquid may be selected when it is desired to disperse the nanoparticulates in the organic liquid during subsequent processing or use. As another example, a polymer may be selected as a permanent matrix material for use in some application. When used as a permanent matrix, the polymer of the matrix may simply provide a structure to retain the nanoparticulate in a desired dispersion without interfering with proper functioning of the nanoparticulates in the application. Alternatively, the polymer may itself also provide some function for the application. The polymer may, for example, have a function that is different than that of the nanoparticulates, have a function that compliments that of the nanoparticulates, or have a function that is the same as that of the nanoparticulates. Examples of some specific combinations of materials for the nanoparticulates and polymer materials for the matrix materials and their applications are described in more detail below. As yet another example, the polymer may be selected for its surface modifying properties to beneficially surface modify the nanoparticulates in a way that is useful in some subsequent processing or use of the nanoparticulates. The invention is not limited to use of any particular polymers in the matrix. Some non-limiting examples of polymers that may be used in the matrix include: fluorinated polymers, thermal curable polymers, UV curable polymers, appended polymers, light emitting polymers, semiconducting polymers, electrically conductive polymers (e.g. polythiophenes, poly (ethylene dioxy thiophene), hydrophobic polymers (siloxanes, polyacrylonitrile, polymethylmethacrylate, polyethyleneterephthalate), hydrophilic polymers (polythiophenes, sulfonated polymers, polymers with ionic functional groups), polyaniline & modified versions, poly pyrroles & modified versions, poly pyridines & modified versions, polycarbonates, polyesters, polyvinylpyrrolidone, polyethylene, epoxies, polytetrafluoroethylene, Kevlar® and Teflon®. The polymers included in the matrix may have any structure, some non-limiting examples of polymeric structures include: dendrimers, long single chain polmers, co-polymers (random or block, e.g. A-B, A-B-A, A-B-C, etc.) branched polymers and grafted polymers.
With reference again to
In some cases, the liquid vehicle may be selected to act as a solvent for one or more than one precursor to be included in the precursor medium, so that in the precursor medium all or a portion of the one or more than one precursor will be dissolved in the precursor medium. In other cases, the liquid vehicle will be selected based on its volatility. For example, a liquid vehicle with a high vapor pressure may be selected so that the liquid vehicle is easily vaporized and removed from the droplets to the gas phase of the gas dispersion during the forming particles 104. In other cases, the liquid vehicle may be selected for its hydrodynamic properties, such as viscosity characteristics of the liquid vehicle. For example, if one or more than one precursor is to be included in the precursor medium in the form of dispersed particulates (such as for example colloidal-size particles dispersed in the liquid vehicle), a liquid vehicle having a relatively high viscosity may be selected to inhibit settling of the precursor particles. As another example, a liquid vehicle with a relatively low viscosity may be selected when it is desired to produce smaller droplets of precursor medium during the generating gas dispersion 102. In still other cases, the liquid vehicle may be selected to reduce or minimize contamination of the particles and/or production of undesirable byproducts during the generating gas dispersion 102 or the forming particles 104, especially when using organic components in the liquid vehicle. As one example, an important embodiment is to use a liquid vehicle that provides fuel for generating heat in a flame reactor. In this example, components of liquid vehicle may be chosen so as to reduce or minimize generation of undesirable byproducts from combustion of liquid vehicle components. Examples of some types of liquids that may be used as or included in a liquid vehicle to provide fuel for a flame reactor include: alcohols, hydrocarbons, acrylates, acrylic acid, carboxylates, carboxylic acid, aldehydes, ketones, and kerosene. In some situations, it may be preferred to select more oxygen-rich liquids (e.g., alcohols, aldehydes, ketones, acids) to reduce the potential for carbon contamination of particles.
The liquid vehicle may be an aqueous liquid, an organic liquid or a combination of aqueous and organic liquids. Aqueous liquids are generally preferred for use as the liquid vehicle in most situations, because of their low cost, relative safety and ease of use. For example, water has the advantage of being non-flammable, and when vaporized during the forming particles 104 does not tend to contribute to formation of byproducts that are likely to complicate processing or contaminate particles. Moreover, aqueous liquids are good solvents for a large number of precursor materials, although attaining a desired level of solubility for some materials may involve modification of the aqueous liquid, such as pH adjustment.
In some situations, however, organic liquids are preferred for the liquid vehicle. This might be the case, for example, when it is desired to dissolve a precursor into the liquid vehicle in situations when the precursor is not adequately soluble in aqueous liquids, or when aqueous liquids are otherwise detrimental to the precursor. For example, an organic liquid vehicle might be necessary to solubilize a number of organic or organometallic precursor materials. Also, as noted above, an organic liquid vehicle might be desirable to provide fuel when a flame reactor is used during the forming particles 104.
In addition to the liquid vehicle, the precursor medium also comprises at least one and often two or more precursors. As noted previously, a precursor is a material that provides at least one component for inclusion in the particles made during the forming particles 104. During the forming particles 104, a precursor may undergo reaction to provide the component for the particles, (e.g., thermally decompose at elevated temperature). Alternatively, a precursor may be processed to provide the component of the particles without reaction, in which case the component provided by the precursor is the precursor material itself. For example, a precursor could process without reaction where the precursor is initially dissolved in the liquid vehicle and a precipitate of the precursor is included in the particles made during the forming particles 104. This might be the case, for example, when the precursor medium initially contains a salt or a polymer dissolved in the liquid medium, which salt or polymer precipitates out to form all or part of the matrix when the liquid vehicle is vaporized during the forming particles 104. As another example, the precursor could volatilize during the forming particles 104 and then condense to form part of the particles made during the forming particles 104. One particular implementation of this example is the use of a salt precursor for the matrix that vaporizes and then condenses onto nanoparticulates after formation of the nanoparticulates. In another particular implementation of this example, precursors for both the nanoparticulate and the matrix could volatilize, react if necessary, and then condense to form materials for inclusion in the multi-phase particles.
Another example of a precursor that may be processed without reaction is a solid material suspended in a liquid vehicle. For example, a precursor could be in the form of colloidal-size particles in the precursor medium, which colloidal particles become part of the multi-phase particles made during the forming particles 104. This might be the case, for example, when the precursor medium contains colloidal silica or colloidal carbon, which colloidal particles then form all or part of the matrix, with or without fusing together of the colloidal particles. Additionally, if useful for subsequent processing or for use in a final application, the colloidal particles in the precursor medium could be surface modified or functionalized. By functionalized, it is meant that chemical functional groups have been attached to the surface of the colloidal particles to provide some specific chemical functionality. Such chemical functionality may be designed to aid in the processing of the precursor to form the particles during the forming particles 104, to aid subsequent processing of particles made during the forming particles, or for some purpose related to the application for which the particles are made during the forming particles 104. Also, particulate precursors may be in a form other than colloidal particles, such as for example in the form of fibers, nanotubes or flakes. As another example, such particulate precursors could be porous particles contained in the precursor medium, which porous particles provide the matrix structure on which the nanoparticulates form during the forming particles 104. Some non-limiting examples of material that may be useful in solid particulate precursor form are porous ceramic materials (such as for example, porous silica, alumina, magnesia), porous carbon, carbon nanotubes and fullerines (e.g., bucky balls)).
In many preferred implementations of the invention, at least one precursor in the liquid medium reacts during the forming particles 104 to provide a component for inclusion in the resulting multi-phase particles.
Table 6 shows some non-limiting examples of some compounds that may be used as precursors, and that would normally undergo reaction during the forming particles 104. The target material for which a listed precursor material provides a component is also listed in Table 6, which materials could be included in either the nanoparticulates or the matrix.
Because of their lower cost, some preferred precursors from Table 6, include nitrates, acetates and chlorides. Not listed in Table 6 are precursors for phosphor materials, which include nitrates, hydroxides and carboxylates of yttrium, gallium, barium, calcium, strontium, germanium, gadolinium, europium, terbium, cerium, chromium, aluminum, indium, magnesium, praseodymium, erbium, thulium, praisadinium, manganese, silver, copper, zinc, sodium and dysprosium. Boric acid may be used with precursors for phosphors as a coreactant and/or a fluxing agent.
The precursor medium may also contain various reagent additives, in addition to the liquid vehicle and precursor(s). As used herein, a “reagent additive” or a “reagent” in the precursor medium is a material, other than the liquid vehicle, that is included in the precursor medium for a reason other than to provide a component for inclusion in the particles made during the forming particles 104. Rather, the reagent additive serves another purpose that is beneficial to formulation of the precursor medium or aids processing to make the particles during the forming particles 104. An example of a reagent additive would be, for example, a base or acid material added to adjust solution pH of the liquid vehicle.
One important example of a reagent additive for some implementations of the invention is a reducing agent. The reducing agent may be in the form of a particulate suspended in the liquid vehicle or, more likely, will be dissolved in the liquid vehicle. The purpose of the reducing agent is to assist creation of an environment during the forming particles 104 that promotes formation of a material in a chemically reduced form that is desired for inclusion in the particles made during the forming particles 104. This might be the case, for example when the desired material is a metal, and the reducing agent is included to promote reduction of a metal oxide to the desired metallic form. A reducing agent does not necessarily reduce an oxidized material to form a desired reduced form of the material, but may simply change the chemistry of the precursor medium to favor the formation of the reduced form of the material, such as by scavenging or otherwise tying up oxidizing materials present in the environment. In some implementations, the reduced form of the material could be made without the use of the reducing agent by processing the gas dispersion at a higher temperature during the forming particles 104, but use of the reducing agent permits the desired reduced form of the material to be made at a lower temperature. An important application is when making particles that include metallic nanoparticulates and matrix including a material that cannot be effectively processed at high temperatures that may be required to prepare the metallic nanoparticles absent the use of a reducing agent. For example, use of a reducing agent may permit the processing temperature to be maintained below the melting temperature of a salt matrix material, or below the decomposition temperature of a polymer matrix material, whereas the processing temperature would exceed those limits without use of the reducing agent. As an alternative to including a reducing agent in the precursor medium, a reducing agent could instead be included in the gas phase of the gas dispersion, such as for example using a nitrogen gas phase or other oxygen-free gas composition with addition of some hydrogen gas as a reducing agent. In other situations, the reduced form of the material could be formed even at the desired lower temperature using a nonoxidizing gas phase in the gas dispersion, such as pure nitrogen gas or some other oxygen-free gas composition. However, by including a reducing agent in the precursor medium, the use of a nonoxidizing gas phase or a reducing agent in the gas phase may often be avoided, and air may instead be used as the gas phase. This is desirable because it is usually much easier and less expensive to generate and process the gas dispersion using air. The reducing agent is typically a material that either reacts to bind oxygen, or that produces decomposition products that bind with oxygen. The bound oxygen often exits in the gas phase in the form of one or more components such as water vapor, carbon dioxide, carbon monoxide, nitrogen oxides and sulfur oxides. Reducing agents included in the precursor medium are often carbon-containing materials, with carbon from the reducing agents reacting with oxygen to form carbon dioxide and/or carbon monoxide. The reducing agent may also contain hydrogen that reacts with oxygen to form water. Table 7 shows some non-limiting examples of reducing agents that may be included in the precursor medium, typically dissolved in the liquid vehicle.
Table 8 shows non-limiting examples of some preferred combinations of reducing agents and precursors that may be included in the precursor medium for manufacture of a variety of metal nanoparticulate materials.
Another important reagent addition that may be included in the precursor medium in some implementations of the invention is an oxidizing agent. The purpose of an oxidizing agent is to help create an environment during the forming particles 104 that is conducive to making a desired oxidized form of a material for inclusion in particles made during the forming particles. The oxidizing agent may provide oxygen in addition to the oxygen that might be present when air is used as the gas phase to make the gas dispersion. Alternatively, the oxidizing agent may be used in combination with a nonoxidizing carrier gas, such as pure nitrogen gas, to provide a controlled amount of oxygen to form the desired oxidized form of the material. One application for such control of the oxidation is when making one oxide of a metal that may form into multiple different oxide forms. For example, a controlled amount of oxygen may be used during the manufacture of magnetite to inhibit formation of the more oxidized iron oxide form of hematite.
Table 9 shows non-limiting examples of some oxidizing agents that may be included in the precursor medium, typically dissolved in the liquid vehicle, such as to assist in the making of oxide materials.
Another reagent addition that may be included in a precursor medium in some situations is a fluxing agent to assist crystal growth or recrystalization of material in the particles made during the forming particles 104. Any of the salts listed in Table 6 may be included in the precursor medium as fluxing agents. A particularly preferred fluxing agent for particles containing phosphor materials is lithium nitrate.
The relative quantities of precursors, liquid vehicle and reagents in the precursor medium will vary, such as for example depending upon the desired composition and morphology of the particles to be produced during the forming particles 104 and the particular feed materials used to prepare the gas dispersion during the generating gas dispersion 102. In most situations, however, the liquid vehicle will be present in the precursor medium in the largest proportion, with the precursor medium typically comprising at least 50 weight percent of the liquid vehicle and often at least 70 weight percent of the precursor medium. The precursor medium comprises at least one precursor to a material for inclusion in the particles made during the forming particles 104, such as material that forms all or part of the nanoparticulates or a material that forms all or part of the matrix. As generated during the generating gas dispersion 102, the gas phase of the gas dispersion may also comprise one or more than one precursor. For example, when making oxide materials, air is often used as the carrier gas to generate the gas dispersion, and the oxygen component of the air is often used as a precursor to provide at least a portion of the oxygen component of the oxide material. The precursor medium will typically comprise, in solution and/or as particulate precursor, no more than about 50 weight percent precursor(s), and preferably no more than about 25 weight percent precursor(s). In most situations, however, the precursor medium will comprise at least 5 weight percent precursor(s). When the precursor medium comprises particulate precursor(s), the precursor medium will typically comprise no more than 20 weight percent of such particulate precursor(s). Moreover, such particulate precursors will typically be of colloidal size, preferably having a weight average size of no larger than about 100 nm and more preferably having a weight average size of no larger than about 50 nm. When the precursor medium comprises dissolved precursors, the precursor medium will typically comprise no more than 25 weight percent of such dissolved precursor(s).
In one preferred embodiment, the precursor medium includes at least two precursors, and even more preferably at least one precursor for a material to be included in the nanoparticulates and at least one other precursor for a material to be included in the matrix. The precursors should be included in the precursor medium in relative proportions to provide the proper relative proportions of the nanoparticulate material and the matrix material in the particles made during the forming particle. The amount of a precursor included in the precursor medium will be selected to provide the desired amount of the final material in the particles. For example, if the multi-phase particles resulting from the forming particle are to contain certain weight percentages respectively of a nanoparticulate material and a matrix material, then the relative quantities of nanoparticulate precursor and matrix precursor must be properly proportioned in the precursor medium to provide the proper weight fractions, taking into account any reactions that are involved in converting the nanoparticulate and matrix precursors into the respective nanoparticulate and matrix materials in the resulting multi-phase particles. In that regard, the particles made during the forming particles 104 will often comprise from 1 weight percent to 80 weight percent nanoparticulates and from 99 weight percent to 20 weight percent matrix.
It should be appreciated, however, that even though the relation proportions of the matrix and nanoparticulate portions of the resulting multi-phase particles may be expressed as weight percentages (or weight fractions), it is the volume percentage (or volume fraction) of these components that is typically more important from a particle engineering standpoint. Weight percentages are often more convenient to use for calculated purposes to determine the relative quantities of precursors to include in the precursor medium. For example, when a nanoparticulate material is significantly more dense than a matrix material (which is frequently the case), then a multi-phase particle may contain a large weight fraction of the nanoparticulate material, but only a small volume fraction of the nanoparticulate material. In most implementations of the invention, the multi-phase particles will comprise a volume percentage of nanoparticulates within a range having in any combination a lower limit selected from the group consisting of 1 volume percent, 5 volume percent and 10 volume percent and an upper limit selected from the group consisting of 60 volume percent, 50 volume percent, 40 volume percent, 30 volume percent and 25 volume percent. One particularly preferred implementation is for the nanoparticulates to comprise up to 30 volume percent and more preferably up to 25 volume percent of the multi-phase particles, but preferably also with at least 5 volume percent and more preferably at least 10 volume percent nanoparticulates. These lower volume fractions tend to favor formation of well dispersed and more completely separated nanoparticulate domains in the multi-phase particles. As the volume percentage of nanoparticulates increases, the separation of the nanoparticulate domains tends to be less complete. For example, with greater than about 50 volume percent of nanoparticulates in the multi-phase particles, an interconnected network of the nanoparticulates may often be favored, such as is described below with respect to
Correspondingly, in most implementations of the invention the multi-phase particles will comprise a volume percentage of matrix in a range having an upper limit selected from the group consisting of 99 volume percent, 95 volume percent and 90 volume percent and having a lower limit selected from the group consisting of 40 volume percent, 50 volume percent, 60 volume percent, 70 volume percent and 75 volume percent. One particularly preferred implementation is for the matrix to comprise at least 70 volume percent and more preferably at least 75 volume percent of the multi-phase particles, but also preferably with no greater than 95 volume percent and even more preferably no greater than 90 volume percent of matrix. In this discussion concerning volume percent, the pore volume in the multi-phase particles are ignored, so that the volumes of the matrix and nanoparticulates are included in determining the total volume of the multi-phase particles used to determine the volume percentages of the nanoparticulates and the matrix. On this basis, the sum of the volume fractions of the nanoparticulates and the matrix add up to 100. It should be appreciated, however, that in some instances the multi-phase particles resulting from the particle forming 104 (
As will be appreciated, in some implementations of the invention, the precursor medium may comprise more than one precursor for one or for each of the nanoparticulates and the matrix. The relative proportions of the nanoparticulate precursor(s) and matrix precursor(s) in the precursor medium will, therefore, vary depending upon the relative proportions of nanoparticulate material(s) and matrix material(s) in the final particles and also on the nature of the particular precursors to those materials that are included in the precursor medium.
The precursor medium should also have properties that are conducive to efficient formation of the desired droplets of the precursor medium during the generating gas dispersion 102. The desired properties of the precursor medium for droplet generation may vary depending upon the specific composition of the precursor medium and the specific apparatus used to generate droplets for the gas dispersion. Some properties that may be important to droplet generation include the viscosity and surface tension properties of the liquid vehicle, the proportion of liquid vehicle and solids, when present, in the precursor medium, and the viscosity, flowability and density of the precursor medium. Some properties, such as viscosity and flowability of the precursor medium, may be affected by the temperature of the precursor medium. Accordingly, if it is desired to reduce the viscosity of the precursor medium to achieve more effective droplet generation, the precursor medium may be preheated to an elevated temperature at which the precursor medium has a reduced viscosity. Alternatively, if a higher viscosity is desired, the precursor medium could be pre-cooled to an appropriate depressed temperature at which the precursor medium has an increased viscosity. Typically, when the droplets are generated, the precursor medium will have a viscosity of less than 1000 centipoise and usually less than 100 centipoise. If the precursor medium contains a particulate precursor, the precursor medium should be sufficiently viscous enough to avoid significant settling of particles in the precursor medium during processing.
As noted previously, the generating gas dispersion 102 includes generating droplets of the precursor medium and dispersing and suspending those droplets in a carrier gas to form the gas dispersion. The droplets may be generated using any appropriate apparatus for finely dividing liquids to produce droplets. Apparatus for generating such droplets are referred to by a variety of names, including liquid atomizers, mist generators, nebulizers and aerosol generators. The technique and apparatus used to generate the gas dispersion may vary depending upon the application.
One example of an apparatus for generating the droplets and mixing the droplets with the carrier gas to form the gas dispersion is an ultrasonic aerosol generator, in which ultrasonic energy is used to form or assist formation of the droplets. One type of ultrasonic aerosol generator is a nozzle-type apparatus, with the nozzle ultrasonically energizable to aid formation of droplets of a fine size and narrow size distribution. Another example of an ultrasonic aerosol generator ultrasonically energizes a reservoir of precursor medium, causing atomization cones to develop, from which droplets of the precursor medium form, and the droplets are swept away by a flowing carrier gas. The reservoir-type ultrasonic aerosol generators can produce very small droplets of a relatively narrow size distribution and are preferred for use in applications when the particles made during the forming particles 104 are desired to be in a range of from about 0.2 to about 5 microns (weight average particle size), and especially when a narrow size distribution of the particles is desired. An example of a reservoir-type ultrasonic aerosol generator is described, for example, in U.S. Pat. No. 6,338,809, the entire contents of which are incorporated by reference herein as if set forth herein in full. Although both the nozzle-type ultrasonic aerosol generator and the reservoir-type ultrasonic aerosol generator produce small droplets of a relatively narrow size distribution, the reservoir-type generally produces finer droplets of a more uniform size.
Another example of an apparatus for generating droplets is a spray nozzle (not ultrasonically energized). Several different types of spray nozzles exist for producing droplets in gas dispersions, and new spray nozzles continue to be developed. Some examples of spray nozzles include 2-fluid nozzles, gas nozzles and liquid nozzles. Spray nozzle generators have an advantage of very high throughput compared to ultrasonic generators. Droplets produced using spray nozzles, however, tend to be much larger and to have a much wider size distribution than droplets produced by ultrasonic generators. Therefore, spray nozzles are preferred for making relatively large particles during the forming particles 104. Other types of droplet generators that may be used include rotary atomizers, and droplet generators that use expansion of a supercritical fluid or high pressure dissolved gas to provide the energy for droplet formation. Still another method for generating droplets is disclosed in U.S. Pat. No. 6,601,776, the entire contents of which are incorporated herein by reference in as if set forth herein in full.
It will be appreciated that no matter what type of droplet generator is used, the size of the particles produced during the forming particles 104 will depend not only upon the size of the droplets produced by the generator, but also on the composition of the precursor medium (such as the concentration and types of precursor(s) in the precursor medium).
As initially generated, the gas dispersion will have a gas phase that is wholly or primarily composed of the carrier gas used to generate the gas dispersion. The gas phase may have some minor components provided by the precursor medium during the generating gas dispersion 102, such as some liquid vehicle vapor from vaporization of some liquid vehicle during the generating gas dispersion 102. The carrier gas may be any convenient gas composition and may be, for example, a single component gas composition (such as for example pure nitrogen gas) or a mixture of multiple gas components (such as for example air, or a mixture of nitrogen and hydrogen). As the gas dispersion is processed, however, the composition of the gas phase will change. For example, during the forming particles 104, liquid vehicle is removed from the droplets to the gas phase, typically by evaporation caused by heating. Also, if the precursor medium contains reactive precursors or reagents, as the precursors or reagents react, the composition of the gas phase will contain decomposition products and reaction byproducts. At the conclusion of the forming particles 104, the gas dispersion will typically comprise an altered gas phase composition and a dispersion of the particles made during the forming particles 104.
In some implementations, the carrier gas used to generate the gas dispersion will be substantially non-reactive during the processing of
Continuing with reference to
Removing liquid from the droplets and reaction of precursor(s) may occur in the same or different equipment. The removing liquid is typically accomplished by vaporizing liquid vehicle, with the liquid vehicle vapor then mixing into the gas phase of the gas dispersion. Vaporization of the liquid vehicle is preferably accomplished by heating the gas dispersion to a temperature at which most, and preferably substantially all, of the liquid vehicle in the droplets vaporizes. In a preferred embodiment, reactions or other processing of precursors to form the desired particles are accomplished in a reactor or reactors. By a reactor, it is meant apparatus in which a chemical reaction or structural change to a material is effected. The removing of the liquid vehicle from the droplets may occur in the reactor or may occur in separate process equipment upstream of the reactor.
Referring again to
In one embodiment of the present invention, removing at least a portion of the liquid vehicle (and perhaps substantially all of the liquid vehicle) from the droplets of precursor medium in the gas dispersion and reacting precursors to form the desired materials for inclusion in the multi-phase particles are performed in separate steps. The removing of the liquid vehicle from the droplets may be performed in a reactor, furnace or using spray drying equipment, to produce a precursor particulate product that is collected for further processing. In some cases, the precursor particulate product made by removing the liquid vehicle from the droplets may not have distinct matrix and nanoparticulate phases, but may contain a single phase of mixed precursor(s) that have not yet reacted to form the matrix and nanoparticulate materials. However, in other cases the precursor(s) to the matrix and the precursor(s) to the nanoparticulates may already be in separate phases. The precursor particulate product made by removing the liquid vehicle from the droplets may then be subjected to a heat treatment in a separate reactor or furnace (e.g. belt furnace, tray furnace or rotary furnace) to react the precursors to form the desired matrix and nanoparticulate materials and to impart the nanoparticulate/matrix structure. It should be noted that in some cases during the heat treatment the matrix material of several particles may fuse together to form a continuous structure of matrix material with dispersed nanoparticulates and no longer be in the form of individual multi-phase particles. If it is desirable to have discrete multi-phase particles, the continuous structure of matrix with dispersed nanoparticulates may be jet milled or hammer milled to form separate multi-phase particles.
One example of a reactor for possible use during the forming particles 104 is a flame reactor. Flame reactors utilize a flame from combustion of a fuel to generate the required heat. In some cases, the precursor medium may contain the primary fuel that is combusted to generate the required heat may contain a supplemental fuel or may contain no fuel for the flame. Flame reactors have an advantage of being able to reach high temperatures. They also have the advantages of being relatively inexpensive and requiring relatively uncomplicated peripheral systems. One problem with flame reactors, however, is that there may be undesirable contamination of particles with byproducts from combustion of the fuel generating the flame. Additionally, there is very little ability to vary and control the environment within the reactor to control the progression of particle formation.
Another example of a reactor for possible use during the forming particles 104 is a plasma reactor. In a plasma reactor, the gas dispersion is passed through an ionized plasma zone, which provides the energy for effecting reactions and/or other modifications in the gas dispersion. Another example of a reactor for possible use during the forming particles 104 is a laser reactor. In a laser reactor, the gas dispersion is passed through a laser beam (e.g., a CO2 laser), which provides the energy for effecting reactions and/other modifications in the gas dispersion. Plasma reactors and laser reactors have an advantage of being able to reach very high temperatures, but both require relatively complicated peripheral systems and provide little ability for control of conditions within the reactor during particle formation.
Another example of a reactor for possible use during the forming particles is a hot-wall furnace reactor. In a hot-wall furnace reactor, heating elements heat zones of the inside wall of the reactor to provide the necessary energy to the gas dispersion as it flows through the reactor. Hot-wall furnace reactors have relatively long residence times relative to flame, plasma and laser reactors. Also, by varying the temperature and location of heat input from heating elements in the different heating zones in the reactor, there is significant ability to control and vary the environment within the reactor during particle formation.
A spray drier is another example of a reactor that may be used during the forming particles. Spray driers have the advantage of having high throughput, allowing large amounts of particles to be produced. However, because of their larger size they provide less of an ability to control the reactor conditions during particle formation.
Referring to
In addition to making particles including matrix and dispersed nanoparticulates, in one aspect the invention also concerns post manufacture processing of the particles that occurs after the forming particles 104. As noted previously, some or all of the material of the matrix in the particles made during the forming particles 104 may be designed to be permanent for some applications of the nanoparticulates. One example of particles using such a permanent matrix material is dispersion of phosphor nanoparticulates in an inorganic oxide matrix (e.g., silica). The multi-phase particles may be used directly, such as for example in the manufacture of a display, to take advantage of the phosphor properties of the nanoparticulates without releasing the nanoparticulates from the matrix. The silica provides a protective environment for the phosphor nanoparticulates without interfering with the excitation of and emission of light from the phosphor nanoparticulates during use in a display application. As another example of an application using a permanent matrix, particles may be made for use as a thermally conductive barrier layer, such as for use in computers. The nanoparticulates could be of a metal with high thermal conductivity, such as silver or copper. The matrix could be of an electrically insulating material, such as an electrically insulating polymer. The combination of electrically insulative polymer matrix and thermally conductive metal nanoparticulates is useful for making thermal interface layers, such as may be used underneath computer chips, permitting rapid dissipation of heat without significant risk of an electrical short through the thermally conductive metal. Another example is use of a matrix as a protective barrier to protect nanoparticulates from degradation. A protective matrix may be useful for protecting organic pigments, inorganic pigments and light emitting materials such as phosphors from the ambient environment (e.g., moisture or oxidation). Other non-limiting examples of multi-phase particles including a permanent matrix material are shown in Table 10, along with exemplary applications for use of those particles.
In one implementation of the invention, however, the particles made during the forming particles 104 will have a matrix that is designed to be wholly or partially removable. In one variation, the removability of the matrix material is an aid to further processing of the nanoparticulates to prepare the nanoparticulates for final use in an application. For example, the matrix may be wholly removable, thereby effecting decomposition of the particles and releasing the nanoparticulates. This may be desirable, for example, when the nanoparticulates need to be modified prior to use (such as for example surface modification for enhanced dispersability), or need to be in a free state for use (for example, for incorporation of the nanoparticulates into a paste or slurry, such as in an ink formulation for ink jet printing). In another variation, a portion of the matrix is removable to leave enough matrix to retain the structure of a particle that maintains the nanoparticulates in a dispersed state in the particle. In a preferred embodiment of this variation, the matrix comprises at least two different materials, with one matrix material being selectively removable relative to another matrix material.
In another implementation of the present invention, the matrix may comprise two or more different materials, with at least one material being selectively removable to produce a controlled pore characteristic (e.g., percent porosity, pore size, permeability) in the remaining particle. In one variation, the matrix may comprise uniformly sized regions of one matrix material that serve as a template to provide a length scale for porosity. The uniformly sized regions of material are then selectively removed to form relatively uniformly sized pores throughout the particle. In one particular implementation of this variation, the matrix is initially composed of two different matrix materials, a salt and a polymer, with the polymer being in the form of substantially uniformly sized particles or beads. When the polymer is selectively removed by being dissolved with a solvent or vaporized in a heater or reactor, leaving the salt matrix material remains with pores of substantially uniform size. The uniformly sized regions of matrix material that aid in forming controlled porosity in the multi-phase particles may, however, be made of any convenient material. Some non-limiting examples of materials that may be used in the matrix to create a template for generating controlled porosity in the multi-phase particles include: large salts, silica or other metal oxide particles, metal particles, zeolites, glasses, polymers (shaped as spheres, e.g., latex spheres; beads; or other shapes) and surfactant salts. Additionally, surfactants can be added to the precursor medium to form micelles (or reverse micelles) that control the size of a matrix material by isolating a matrix precursor within the micelles and constraining the size of the domains of the matrix material that is formed during the forming particles 104.
In yet another implementation of the invention, the matrix is designed to be wholly removable and merely serves as an aid for delivering the nanoparticulates into a final application or product. For example, in catalytic applications it might be useful to have a porous network of nanoparticulates of a catalyst material deposited on a catalytic support surface. However, such a network of nanoparticulates might be difficult to form directly on the surface. Using one embodiment of the present invention, multi-phase particles containing a matrix and an interconnected network of nanoparticulates, such as shown and described below with respect to
Referring now to
Removal of matrix material may be effected in any convenient way that effectively destroys the structure of the particles to release the nanoparticulates. As one example, matrix material may be removed by chemical reaction of, or reacting away the matrix material. The particles are subjected to reactant(s) that react with one or more materials of the matrix, thereby removing matrix material from and decomposing the particles. Table 11 shows some non-limiting examples of combinations of matrix materials and reactants or stimuli resulting in reaction of a matrix material to effect removal of the matrix material.
As another example, matrix material may be removed by sublimation of the matrix material. The particles are subjected to conditions of temperature and pressure, which may be a vacuum pressure, at which the matrix material sublimes. Some non-limiting examples of sublimable matrix materials include lower molecular weight organic materials and oxides of lead, bismuth, vanadium, antimony and tin.
In one preferred embodiment, during the decomposing particles 116, sufficient matrix material is dissolved into a liquid medium to effect the decomposition of the particles. For example, salt matrix materials, such as those listed in Table 6, may be dissolved into aqueous liquids. As another example, a polymer matrix could be dissolved into an organic liquid, or aqueous liquid, depending upon the polymer. In any event, it is important that the liquid medium be selective for dissolving the matrix material relative to the nanoparticulates, so that material from the nanoparticulates is substantially not dissolved into the liquid medium. The dissolution of the matrix material in a liquid medium may be performed using any adequate method or apparatus such as for example a stirred tank or other equipment that agitates the liquid medium to promote contact of the liquid medium with the multi-phase particles.
With continued reference to
When the particles are made during the forming particles 104 to include a dispersing agent, a precursor for the dispersing agent will typically be included in the precursor medium from which droplets are formed during the generating gas dispersion 102. For example, a polymer for use as the dispersing agent could be dissolved in the liquid vehicle, with the polymer precipitating out and being included in the particles during the forming particles 104. Alternatively, the dispersing agent may be a material that is formed during the forming particles 104 from reaction of precursor(s) included in the precursor medium and/or the carrier gas. For example, a monomer or monomers for a polymer (which may be a homopolymer, copolymer, terpolymer, etc.) to be used as a dispersing agent may be included in the precursor medium, which monomer(s) polymerize to form the dispersing agent during the forming particles 104.
An alternative to including the dispersing agent in the particles made during the forming particles 104 is for the dispersing agent to be present in the liquid medium when initially contacted with the particles during the decomposing particles 116, or to add the dispersing agent to the liquid medium after such initial contact, but preferably prior to completion of the decomposing particles 116. In a preferred variation of this alternative, the dispersing agent is predissolved into the liquid medium prior to contacting the liquid medium with the particles during the decomposing particles 116, so that the dispersing agent is immediately available to intimately contact and associate with the nanoparticulates as they are exposed during the decomposing particles 116. During the decomposing particles 116, the mixture of liquid medium and particles is preferably agitated, such as with a mixer, to promote effective decomposition of the particles and intimate contact between the nanoparticulates and the dispersing agent.
Contacting the nanoparticulates with a dispersing agent in a liquid medium during or following the decomposing particles 116 is one example of post manufacture modification of the nanoparticulates, in that the dispersing agent effects a surface modification of the nanoparticulates to inhibit agglomeration and promote dispersibility. Another example of post manufacture modification of the nanoparticulates is contacting the nanoparticulates with a dispersing agent or other surface-modifying agent in a fluidized bed following the decomposing particles 116. The present invention, however, provides significant flexibility to effect a variety of post-manufacture modifications to one or both of the nanoparticulates and the matrix.
Referring now to
One type of surface modification that may be performed on the nanoparticulates is coating or covering a surface of the nanoparticulates with a material that masks, or otherwise modifies, the surface properties of the nanoparticulates. By coating a surface it is meant covering a portion or all of the surface with surface-modifying material(s), also referred to herein as surface-modifying agents. A surface-modifying material may be held in association with the surface by any mechanism, including physical absorption, chemisorption or attachment through chemical bonding to the surface of the nanoparticulates (e.g., through covalent or ionic bonding). The surface-modifying material may perform one or a number of functions at the surface of the nanoparticulates. The surface-modifying material may function as a surfactant to modify the surface properties. The surface-modifying material may function as a dispersing agent to promote uniform separation and dispersion of the nanoparticulates in a liquid medium. The surface modifying material may function as a stabilizer to inhibit chemical degradation of the nanoparticulates.
Table 12 shows some non-limiting examples of polymers that may be used as surface-modifying materials to coat the surface of metal oxide, metal and semiconductor nanoparticulates.
Table 13 shows some additional non-limiting examples of surface-modifying materials that could be used during the surface modifying 118. The surface modifying materials listed in Table 13 are materials that would normally associate with a surface of nanoparticulates by a mechanism other than through chemical binding (e.g., adhesive).
In one embodiment of the implementation of the invention shown in
Non-limiting examples of some chemical functional groups that may be used to functionalize the nanoparticulates include hydroxyl, carboxyl, sulfo, oxo, amine, amide, acyl, alkyl, vinyl, carbonate, ammonium, sulfate, sulfhydryl, carbonyl, silyl, siloxy, acetyl, and any substituted form of any of the foregoing. In some embodiments of the present invention, functional groups may be attached to the surface of the nanopaticulates for the purpose of forming a precursor to a material on the surface of the nanoparticulates. This may be useful for example in an ink composition used in forming conductive features on a substrate. Ink compositions used in forming conductive features on a substrate may contain conductive particles that once deposited on a substrate in a desired pattern, are heated to fuse the particles together to form an electrically conductive feature. In one embodiment of the present invention, a nanoparticulate made of a conductive material may be functionalized with a chemical functional group that is then reacted to form a precursor to a conductive material on the surface of the nanoparticulates. When the nanoparticulates, with such a precursor on their surface, are used in an ink that is deposited on a substrate and heated, the precursor material on the surface of the nanoparticulates reacts to form the conductive material, which aids in fusing the nanoparticulates together and forming a conductive feature.
Non-limiting examples of some types of functionality that may be imparted to the nanoparticulates by the functional group include metal addition, hydrophilicity, hydroprobicity, lipophilicity, dispersibility in or compatibility with any desired material with which the nanoparticulates may be subsequently contacted or combined during subsequent processing or use. Also, the functional group may be selected to provide a reactive site for further modification at a later time. For example, the functional group may provide a reaction site for later grafting a polymer segment or a site for initiation of a polymerization reaction to form a polymer segment at the reactive site.
One preferred example of functionalizing nanoparticulates is attaching hydrophobic groups to metal or metal oxide nanoparticulates for enhanced compatibility with, and/or dispersibility in, an organic medium such as dispersion in an organic liquid or a polymer composition. For example, the hydrophobic groups may be attached by substitution at hydroxyl sites on the surface of the nanoparticulates such as through use of a silane coupling agent or some other coupling agent. As another example, polymer segments may be grafted to the surface of the nanoparticulates directly, or through the use of a coupling agent, in order to make the nanoparticulates more compatible with and dispersible in a particular polymer, aiding the preparation of a homogeneous blend of the nanoparticulates in a composition of the particular polymer. In the first example, the modified nanoparticulates may be more easily dispersible in an organic liquid to form a homogeneous composition, such as for preparation of an ink composition for ink jet printing.
As noted, the nanoparticulates may be modified by attaching directly, or through the use of some intermediate linking group, a group containing a reactive site for subsequent modification. The reactive site may be a site, for example, for polymerization, for grafting polymer segments, for cross-linking in a cross-linked polymer network or an ionic site for ionic bonding with other materials or for ion exchange.
Another type of surface modification that may be performed during the modifying nanoparticulates 118 is removal of surface groups or characteristics from the nanoparticulates. One example of this is dehydroxylating the surface of metal or metal oxide nanoparticulates to remove hydroxyl functionalization that may have formed on the nanoparticulates.
A compositional modification that may be performed during the modifying nanoparticulates 118 involves changing the composition in the interior of the nanoparticulates. For example, a metal oxide material contained in the nanoparticulates may be compositionally modified by reduction to form a metallic material (e.g., silver oxide to silver, nickel oxide to nickel). Conversely, a metallic material contained in the nanoparticulates may be oxidized to form a metal oxide material. As another example, when the nanoparticulates contain a monomer, the monomer may be polymerized to form a polymer. As another example, pre-polymer blocks in nanoparticulates could be linked together or cross-linkable polymers in the nanoparticulates could be cross-linked. As yet another example, a dopant could be diffused into a material of the nanoparticulates, such as to form a semiconductor or phosphor material with a specific desired property.
Structural modification that may be performed during the modifying nanoparticulates 118 involves a non-compositional, physical change to the nanoparticulate crystallinity or particle morphology. Such structural modification often involves subjecting the nanoparticulates to a thermal treatment at elevated temperature. As one example, structural modification may involve annealing the nanoparticulates, such as for crystal growth, to change the crystallinity or to redistribute materials within the nanoparticulates. Another example of a structural modification is changing the size of the nanoparticulates, which may involve a heat treatment to grow the size of the nanoparticulates.
It should be appreciated, that the modifying nanoparticulates 118 may involve one or more than one of any number of surface modifications and/or compositional modifications and/or structural modifications. As an example, the nanoparticulates could be annealed in the presence of a reactive component to effect both a compositional change and a physical change.
The modifying nanoparticulates 118 may be performed while the nanoparticulates are maintained in a dispersed state in the multi-phase particles made during the forming particles 104, after modifying the matrix of the multi-phase particles, or after decomposing the multi-phase particles to release the nanoparticulates. Also, the modifying nanoparticulates 118 may involve multiple modifications to the nanoparticulates. For example, one or more modifications may be performed to the nanoparticulates while the nanoparticulates are maintained in a dispersed state within the particles made during the forming particles 104; one or more additional modifications may be performed on the nanoparticulates during decomposition of the multi-phase particles and one or more modifications may be performed on the nanoparticulates after decomposition of the multi-phase particles 116 to release the nanoparticulates (such as for example surface modifying the nanoparticulates by contacting the nanoparticulates with an appropriate surface modifying material in a fluidized bed after release of the nanoparticulates from the matrix).
Referring now to
The modifying nanoparticulates step 118 may be performed while the particles are still in the gas dispersion. Thus, the modifying nanoparticulates step 118 may be performed in series after the forming particles step 104 without intermediate collection of the particles. One example of this is annealing or calcining the particles on-the-fly in the gas dispersion. Alternatively, the modifying nanoparticulates 118 could be performed after removal of the particles from the gas dispersion. One example of this is annealing or calcining the particles in a kiln, rotary calciner, belt furnace or tray furnace after collection of the particles. In some cases during the annealing or calcining, the matrix material from several multi-phase particles may fuse together to form a continuous structure of matrix with dispersed nanoparticulates. If it is desirable to have discrete multi-phase particles, the continuous structure of matrix with dispersed nanoparticulates may be jet milled or hammer milled to form separated multi-phase particles.
Referring now to
Referring now to
Referring now to
One particularly preferred embodiment involving modifying the matrix is to remove only a portion of the matrix to increase porosity in the matrix and enhance access to the nanoparticulates through the increased porosity. The matrix with increased porosity may be a permanent matrix, and the increase in porosity may be useful for a final application. For example in catalytic applications, a porous matrix is useful to provide access to catalytic nanoparticulates dispersed in the porous matrix. Alternatively, the matrix with increased porosity may be a temporary, non-permanent matrix, and the enhanced porosity may be useful to provide access to the nanoparticulates to modify the nanoparticulates, (e.g., surface modification, compositional modification and/or structural modification). The increased porosity enhances infiltration of treating chemicals and reagents that may be used to modify the nanoparticulates.
The matrix could initially be composed of a single material with the increase in porosity being effected by removal of a portion of the matrix, (e.g., partial dissolution of the single matrix material). In another, preferred implementation however, the matrix initially comprises multiple materials with one matrix material being selectively removable relative to another matrix material to effect the increase in matrix porosity. The selective removal may be performed, for example, by selective sublimation, selective dissolution into a liquid medium, selective chemical removal, selective thermal decomposition at elevated temperature or selective melting of one matrix material relative to the other matrix material. By selective chemical removal it is meant that the matrix material is reacted with one or more reactants to form reaction products that are removed from the matrix, while the other matrix material is substantially not removed.
The selective removability of the matrix materials requires that the materials be selected to have different properties in relation to the removal technique to be used, with one material being substantially removable by the technique and the other being substantially not removable by the technique. For example, the matrix could contain one material that dissolves into a particular liquid medium and another material that does not dissolve into that liquid medium. As one example, a first matrix material may be a water soluble salt and a second matrix material may be a water insoluble polymer, with the selective removal being effected by dissolving at least a portion, and preferably substantially all, of the first matrix material into an aqueous liquid. As another example, the selective removal of the second matrix material could be effected by dissolving the polymer into an organic solvent in which the salt is substantially insoluble. As another example, the matrix could comprise two different inorganic salts with different solubilities in an aqueous liquid. As another example, the matrix could comprise two polymers with different solubilities in an aqueous or organic liquid. As another example, the matrix could comprise an inorganic salt or polymer that is soluble in a liquid medium and an inorganic oxide material (e.g., silica) that is not soluble in the liquid medium.
The partial removal of the matrix may be performed in a gas dispersion. For example, the partial removal of the matrix may be performed in series following the forming particles 104 while the particles are in the same gas dispersion. Alternatively, the partial removal of the matrix may occur after collection of the particles, which particles may then be re-dispersed in a new carrier gas to form a new gas phase in which the partial removal of the matrix is performed. As another alternative, the partial removal of the matrix may occur in an environment other than a gas dispersion. For example, after collection of the particles from the gas dispersion, the particles may be mixed with a liquid medium that is a selective solvent for one of the matrix materials.
One aspect of the invention involves removing nanoparticulates from a matrix structure and re-dispersing the nanoparticulates in a new medium. The re-dispersion may be in a new matrix or in a selected liquid medium. In one embodiment, at least a portion of the matrix, and preferably substantially all of the matrix, is removed using a liquid medium, with corresponding release of the nanoparticulates into the liquid medium, followed by separation of the nanoparticulates from the liquid medium and then re-dispersion of the nanoparticulates in a new liquid medium or in a new matrix.
With continued reference to
Another aspect of the present invention involves re-dispersing nanoparticulates in a composite structure with a new matrix. The matrix of the multi-phase particles as manufactured during the forming particles 104 may be useful for subsequent processing, handling, transportation or storage of the nanoparticulates, but it may be desirable at same point to have a different matrix for further processing, handling, storage or transportation, or for a final application for use of the nanoparticulates. The new matrix may be a permanent matrix for a final use or it may be a non-permanent temporary matrix for intermediate handling, storage, transportation or further processing.
As with the matrix of the particles described previously, the matrix of the composite structure may be comprised of a single material or of multiple materials that function to maintain the nanoparticulates in a dispersed state. The new matrix of the composite structure may have the same composition or a different composition than the matrix removed during the decomposing particles 116. More often, the new matrix of the composite structure will have a different composition than that of the matrix removed during the decomposing particles 116, because the new matrix in the composition structure will typically serve a different purpose. The new matrix of the composite structure may include any suitable materials for a desired purpose. Examples of materials previously identified for the particles, made during the forming particles 104, are examples of materials that may be used for the new matrix of the composite structure.
Any procedure useful for dispersing nanoparticulates in a matrix may be used during the forming composite structure 134. As one example, the nanoparticulates may be dispersed in a melt of matrix materials and then cooled to solidify the composite structure (e.g., dispersed in a polymer melt). As another example, the nanoparticulates may be mixed with and dispersed in a new liquid medium, with the matrix then being formed around the dispersed nanoparticulates. As a specific example, nanoparticulates may be dispersed in a solution of reactable monomers or pre-polymer segments that are then polymerized or otherwise reacted to form the matrix around the dispersed nanoparticulates. As a further example, nanoparticulates may be dispersed in a polymer solution that gels upon inducing some change in the system. The polymer solution may change from a liquid to gel form, for example, in response to a change in temperature, pH or light. As another example, nanoparticulates may be dispersed in a solution of cross-likable polymer that is then cross-linked to form the matrix around the dispersed nanoparticulates. As yet another example, the nanoparticulates may be dispersed in a liquid medium that includes colloidal particles of inorganic oxide (e.g., silica), and then liquid may be removed (e.g., evaporated) to form a matrix comprising the inorganic oxide. As another example, the nanoparticulates may be dispersed in a precursor solution comprising a reactable precursor material for the matrix and the precursor may be reacted to form the matrix material (e.g., dissolved precursor for making silica or another inorganic oxide).
In one implementation, the composite structure is made in particulate form by gas dispersion processing during the forming composite structure 134. Droplets comprising the nanoparticulates, and preferably also comprising one or more precursors for the new matrix, are formed and dispersed in and suspended by a carrier gas to form a new gas dispersion. The droplets are formed from a feed medium comprising the nanoparticulates dispersed in a liquid vehicle. Precursor(s) for material(s) of the new matrix are preferably dissolved or suspended in a liquid vehicle, but precursor(s) for material(s) of the new matrix may also be included in the carrier gas. In the gas dispersion, liquid is removed from the droplets and the precursors for the new matrix are reacted or otherwise processed to form the new matrix. The new gas dispersion may be made, for example as previously discussed with respect to forming the gas dispersion during the generating gas dispersion 102. Examples of liquid vehicles and matrix precursors that may be included in the feed medium are similar to those described previously with respect to the generating gas dispersion 102. After particles of the composite structure have been made in the new gas dispersion, the particles may be collected for further processing or use. The collection of the particles involves separating the particles of the composite structure from the gas phase of the new gas dispersion, such as by cyclone, filter, electrostatic precipitation, or in a bag house.
The composite structure made during the forming composite structure 134 may be designed as a permanent structure for a final use or may be a temporary structure useful for intermediate storage, transportation, handling or further processing of the nanoparticulates prior to final use. One example of a composite structure designed for final use is a dispersion of thermally conductive metal nanoparticulates (such as copper or silver) in a polymer matrix for use as a thermal interface material.
Referring again to
In one preferred embodiment of the implementation of
One advantage of collecting the particles directly into a liquid medium is inhibition, and preferably prevention, of agglomeration of the particles, which may occur with other collection techniques. More importantly, many implementations of the present invention include processing the particles in a liquid medium, and collecting the particles directly into a liquid medium can significantly simplify the processing. For example, if the particles are collected directly into a liquid medium of a type to be used for processing, this eliminates the need to collect and then disperse the collected particles in the liquid medium. The dispersion in the liquid medium has been accomplished as part of the collection. After the particles have been collected into the desired liquid medium, then reagents/reactants may be added to the liquid medium for desired processing (e.g., for modification of nanoparticulates or matrix). Alternatively, at the time of particle collection, the liquid medium may already have one or more reagents and/or reactants for such processing.
In one embodiment of the implementation of
In another variation of collecting particles directly into a liquid medium during the collecting particles 136, the liquid medium as used during the collecting particles 136 may be a solvent for one or more materials of the matrix and also contain one or more reactants and/or reagents for performing a modification of the nanoparticulates. Such a modification could involve, for example, a surface modification, compositional modification and/or structural modification of the nanoparticulates or the matrix, in a manner as previously discussed. For example, the liquid medium may contain a surface-modifying material, such as a dispersing agent, that surface modifies the nanoparticulates in the liquid medium of the collection. As another example, liquid medium used for collection may include reactants for use in attaching functional groups to the surface of the nanoparticulates, or reactants for use to compositionally modify the nanoparticulates.
In one embodiment of the process implementation shown in
In another embodiment of the process shown in
Another aspect of the present invention involves manipulation of multi-phase particles (such as for example those made during the forming particles 104 or made by another route) that include a dispersion of nanoparticulates and matrix, with the nanoparticulates maintained in a dispersed state by the matrix. Such manipulation may be, for example, as an aid to handling, storage, transportation, further processing or use of the nanoparticulates. This aspect of the invention includes any and all of the different operations discussed above (e.g.,
Another aspect of the invention concerns making a formulation comprising nanoparticulates and a liquid medium and involves forming a mixture comprising multi-phase particles and liquid medium, the multi-phase particles comprising nanoparticulates maintained in a dispersed state in the multi-phase particles by matrix; treating the multi-phase particles while in the mixture; and removing solutes from the liquid medium to thereby reduce the concentration of the solutes in the mixture, and preferably to reduce the molar concentration of the solutes by at least a factor of 10. The treating of the multi-phase particles may involve any treatment that may be performed in a liquid medium, including for example, decomposing the multiphase particles to release the nanoparticulates or any of the modification to the multiphase particles discussed above (such as any of the modifications to the matrix and/or nanoparticulates as discussed above), or some other treatment. The performing of such a treatment often results in solutes in the liquid medium. The solutes may include, for example, one or more of: residual treating material left over from the treatment, matrix material or nanoparticulate material dissolved into the liquid medium during the treatment, and reaction or decomposition products produced during the treatment. The multi-phase particles subjected to the treatment are preferably made as described herein, but may be made by another route.
Reference is now made to
With continued reference to
Also, although the treating particles 146 and removing solutes 148 are shown as being sequential, the steps may be performed partially or wholly simultaneously. For example, solutes may be removed from the liquid medium while the multi-phase particles are being subjected to the treatment to immediately commence removal of solutes as they begin to build up in the liquid medium.
The removing solutes 148 may be performed by any technique. One preferred technique is membrane separation of the solutes by preferentially passing the solutes through a semipermeable membrane relative to particulates in mixture with the liquid medium. The particulates may comprise, for example, modified forms of the multi-phase particles or nanoparticulates that have been released from the matrix structure through decomposition of the multi-phase particles. By semipermeable membrane, it is meant that the membrane is significantly more permeable to passage of the solutes to be removed than passage of the particulates. Passage of the solutes across the membrane may be due to unaided diffusion of the solutes through the membrane, or
the membrane may be functionalized or contain ion exchange activity to facilitate transport of one or more solutes across the membrane. For example, dissolved salt ions, from dissolution of a salt matrix may be removed in a dialysis-type membrane separation. Likewise, special molecule polymers may also be removed in such a dialysis-type membrane separation. For larger polymers, or macromolecules, a diasolysis or other membrane separation technique may be used. Examples of some membranes that may be used for removing smaller molecule solutes include, for example parchment membranes, collodion, cellophane, asbestos fiber and perfluorosulfonic acid membrane (such as NAFION™ membranes from DuPont). For removal of larger polymer molecules, some examples of some membranes that may be used include gum, plastic or rubber membranes. Another technique is to partition target solutes into another liquid that is immiscible with the liquid medium. For example, some polymer solutes could be partitioned into an organic liquid that is immiscible with the liquid medium, such as for example when the liquid medium is an aqueous liquid.
Another aspect for the present invention concerns particulate product comprising multi-phase particles that comprise a dispersion of nanoparticulates and matrix, with the nanoparticulates maintained in a dispersed state by the matrix. The nanoparticulates may have any composition, including any composition as discussed previously. Likewise, the matrix may have any composition, and may be comprised of any material or materials that function to maintain the nanoparticulates in the dispersed state, as discussed previously. Moreover, the multi-phase particles may have any of the attributes described previously, including any attributes imparted by any modifications of the multi-phase particles described previously, including any modifications to the matrix and/or nanoparticulates.
In one variation of the particulate product of the invention, the matrix of the multi-phase particles comprises multiple materials.
It will be appreciated that
Typically, the multi-phase particles of the present invention are spheroidal, meaning that they are generally of spherical shape, even if not perfectly spherical.
In another variation of the particulate product of the invention, the particulate product comprises multi-phase particles in which some or all of the nanoparticulates comprise one or more precursors that are reactable to modify the nanoparticulates while the nanoparticulates are maintained in the dispersed state. The modification may involve surface modification of the nanoparticulates, such as functionalization. Alternatively, the modification may involve compositional modification. As one example, the nanoparticulates could comprise monomers that are polymerizable while held by the matrix to form polymers in the nanoparticulates. As another example, the nanoparticulates could comprise a metal oxide that is reducible to form metallic material in the nanoparticulates. The reduction could be accomplished, for example, by thermal treatment at an elevated temperature and/or by introduction of a reducing agent, such as hydrogen gas that is infiltrated into the matrix to contact the nanoparticulates.
In another variation of the particulate product of the invention, the particulate product comprises multi-phase particles that comprise a surface-modifying material, which may be present in the matrix, nanoparticulates, or elsewhere in the multi-phase particles. The multi-phase particles are decomposable to release the nanoparticulates, with at least a portion of the surface-modifying material associating with the nanoparticulates to modify the surface of the nanoparticulates. As one example, the surface modifying material may be a residual surfactant or dispersing agent that adheres to the surface of the nanoparticulates. In another example, the surface-modifying material is reactable with a surface of the nanoparticulates, before, during or after decomposition of the multi-phase particles, to attach functional groups to the surface of the nanoparticulates through chemical bonding.
In another variation of the particulate product of the invention, the particulate product comprises multi-phase particles in which some portion or substantially all material of the matrix is removable by a technique other than by dissolution in a liquid. Matrix material may be removable, for example, by sublimation, melting, decomposition or chemical removal (e.g., by reacting the material away).
EXAMPLES Example 1 Iron Oxide Nanoparticulates and Salt MatrixSeveral precursor mediums are prepared containing: Fe(NO3)3.9H2O, as a precursor to iron oxide nanoparticulates; a salt, NaNO3 or NaCl, as a precursor to a matrix material and deionized water. The precursor mediums are processed into a powder containing multi-phase particles including iron oxide nanoparticulates in a salt matrix, which is dissolved away in a subequent step. The weight ratio of Fe(NO3)3.9H2O to salt in the precursor mediums is varied between 1:2 and 1:8, based on the final amount of iron oxide desired in the multi-phase particles. The precursor mediums are processed using a spray pyrolysis system that generates droplets of the precursor mediums, using an ultrasonic generator, and heats the droplets in a tubular hot wall reactor at temperatures ranging from 400° C. to 1000° C. The processing conditions for the production of the powders containing the multi-phase particles are summarized in Table 14.
Thermogravimetric analysis (TGA) of the Fe(NO3)3.9H2O precursor and the NaNO3 salt matrix component indicates that the decomposition of Fe(NO3)3.9H2O to iron oxide occurs stepwise, wherein the water is first stripped off and then the nitrate is converted to iron oxide. The conversion temperature for the Fe(NO3)3 precursor is relatively low, below about 200° C.
After production of the powders containing the multi-phase particles, the nanoparticulates are subjected to a heat treatment using two different methods. In one method, the nanoparticulates are heat treated prior to being separated from the salt matrix. In a second method, the nanoparticulates are heated after separating the nanoparticulates from the matrix in a separation step. Because the salts NaNO3 and NaCl used as matrices are highly soluble in water, the separation step involves dissolving away the salt matrix using water. The salt matrix is dissolved by repeated additions of water followed by settling or centrifugation of the nanoparticulates released from the matrix. An alternative method of separating the nanoparticulates from the matrix is to filter and wash the nanoparticulates, which form soft agglomerates, several times with water to remove the matrix material.
The powders containing the multi-phase particles are tested using x-ray diffraction (XRD) to determine which phases are present in the powders. Table 14 shows the phases that are detected in the powders. Some of the iron oxide nanoparticulates produced from the precursor mediums are magnetic.
It is expected that the use of two different matrix salts will result in particles of different particle size and morphology because NaCl melts 500° C. higher than NaNO3.
Precursor mediums processed at or below 800° C. yield powders with crystalline salt matrices (NaCl or NaNO3) and amorphous iron oxide. Crystalline phases of both the iron oxide and the matrix material, when NaCl is used as the matrix, are detected from powders that are processed at a temperature of 1000° C. It is likely that some of the NaNO3 matrix melts or decomposes when processing the precursor mediums between 400° C. and 700° C.
Powders with NaCl as Matrix of Multi-Phase Particles
A crystalline phase of NaNO3 appears in the XRD spectra of powders produced from the precursor medium containing NaCl and processed at 400° C. The presence of the crystalline phase of NaNO3 is probably due to the simultaneous precipitation of NaNO3 and FeCl3 during processing of the precursor medium. The FeCl3 decomposes to iron oxide at about 315° C. For powders processed at higher temperatures, the only crystalline salt phase detected is NaCl. It is believed that the NaNO3 is not present in the powders processed at higher temperatures because it melts and decomposes at the higher temperatures.
Scanning electron microscope (SEM) images of the powder, made from the precursor medium containing NaCl, before separation of the nanoparticulates from the matrix, show multi-phase particles mainly in the size range between 0.5 μm and 5 μm, as would be expected from the ultrasonic generation method. The particles are mostly spherical shaped with an uneven surface structure. Individual domains within the multi-phase particles are visible, indicating the heterogeneity of the multi-phase particles. An increased presence of smaller multi-phase particles (200 nm to 500 nm) is observed for powders processed at 1000° C., which may be caused by bursting of larger particles during processing.
SEM images of the multi-phase particles indicate that the iron oxide formed at lower temperatures appears as mostly spherical nanoparticulates in the size range between 50 nm and 200 nm. At higher processing temperatures smaller nanoparticulates, that are partially sintered and form larger agglomerates after separation from the matrix, are formed. A variety of different morphologies are observed at a processing temperature of 1000° C., such as irregularly shaped multi-phase particles, small nanoparticulates sintered together to make up secondary agglomerates and porous shells that are mostly spherical or broken into smaller pieces.
An analysis is performed on the particle morphology of the multi-phase particles produced from the precursor mediums with ratios of Fe(NO3)3.9H2O to NaCl of 1:4, 1:2 and 1:8. The analysis indicates distinct crystalline facets for sample L (1:4 ratio), indicating the presence of cubic phased NaCl. Thin broken shells are observed in sample L and are attributed to iron oxide. The thin broken shells are also observed after dissolution of the NaCl in the multi-phase particles to separate the nanoparticulates. The decreased relative amount of Fe(NO3)3.9H2O in sample L (compared to sample H, with a 1:2 ratio) leads to the formation of thinner shells that break up more easily. This effect is even more pronounced at lower Fe(NO3)3.9H2O to NaCl ratios such as sample K (1:8 ratio).
A higher amount of smaller NaCl matrix material forms at high temperatures and low precursor to matrix ratios such as in sample K. One interpretation is that initially individual smaller domains of NaCl form from larger droplets separated by an iron nitrate phase. However, because most of the iron nitrate migrates to the surface during the course of the conversion, gaps are formed and at higher temperatures the larger particle bursts into smaller spherical particles consisting of matrix material and thin broken shells of iron oxide.
The above analysis indicates that the preferred process conditions for the preparation of iron oxide nanoparticulates in a NaCl matrix include the use of lower temperatures since higher temperatures lead to an increased droplet drying rate which causes the Fe(NO3)3.9H2O to migrate to the surface where it nucleates and crystallizes. Keeping the residence time constant and lower temperatures provide more time for the Fe(NO3)3.9H2O to precipitate and convert within the NaCl matrix rather than at the surface. A high Fe(NO3)3.9H2O to NaCl ratio is preferred since it leads to higher yield of nanoparticulates and better separation without a negative effect on the particle size.
Powders with NaNO3 as Matrix of Multi-Phase Particles
Different results are observed when NaNO3 is used as the matrix material. The powders processed at 400° C. are analyzed with an SEM to view the nanoparticulates before and after separation from the NaNO3 matrix. In contrast to the samples using a NaCl matrix at the same temperature and precursor to matrix ratio (overall solution concentration not considered), the average particle size of the amorphous iron oxide nanoparticulates is larger, around 300 nm and the shape is distinctively spherical and only moderate agglomeration occurs.
The nanoparticulates produced at 400° C. are separated from the NaNO3 matrix by settling and centrifugation. However, when separated by filtration instead of settling and centrifugation the SEM images show larger agglomerates. Agitation of the agglomerates by, for example, ultrasonication breaks up these agglomerates. It is also noted that accelerated drying of the nanoparticulates after dissolving of the NaNO3 matrix leads to agglomeration.
Processing at higher temperatures of 500° C. to 700° C. provides inconclusive results, and it is not clear if the combination of Fe(NO3)3 with a NaNO3 matrix is useful at higher temperatures.
Processing at 1000° C. creates multi-phase particles with iron oxide nanoparticulates having significant crystallinity. However, the multi-phase particles processed at 1000° C. have size and morphology characteristics that are not ideal. Multi-phase particles with more favorable characteristics are obtained at lower temperatures. Consequently, the multi-phase particles may be formed at lower temperatures and then to increase the crystallinity of the nanoparticulates, a post treatment step may be performed (e.g., heat treatment). The post treatment step may be performed on the nanoparticulates after separation from the matrix. Alternatively, the nanoparticulates may be subjected to the post treatment prior to separation from the matrix.
Example 2 Phosphor Nanoparticulates and Salt Matrix Precursor mediums are prepared for making powders containing multi-phase particles with phosphor nanoparticulates, having the general composition Na(Y,Yb,Er)F4 nominally including 69 mol % Y, 30 mol % Yb and 1 mol % Er. The following precursors are included in the precursor mediums: Y2(CO3)2.xH2O, Er2(CO3)3.xH2O, Yb2(CO3)3.xH2O and NaHCO3. As a first step to the preparation of the precursor mediums, HOfAc is added to the carbonate precursors to form the corresponding metal trifluoracetates. Complete reaction of the precursors to the metal trifluoracetates is indicated by the presence of a clear precursor solution. A matrix precursor is then dissolved in the clear precursor solution. NaNO3, NaF or NaCl are dissolved in the precursor medium as precursors for a salt matrix. The different precursor mediums prepared are listed in Table 15. Each precursor medium also includes an excess of HOfAc.
The precursor mediums are processed to produce powders containing multi-phase particles. The precursor mediums are processed using a spray pyrolysis system. The spray pyrolysis system includes an ultrasonic generator that generates a gas dispersion containing droplets of the precursor medium in a carrier gas. The gas dispersion is then heated in a tubular hot wall reactor to form the multi-phase particles, which are collected on a heated filter plate. Some samples are processed using an impactor to narrow the size distribution of the droplets of precursor medium in the gas dispersion prior to heating the droplets in the tubular hot wall reactor. The processing conditions for each sample are listed in Table 16.
Some of the powders containing the multi-phase particles are characterized using XRD. Also, for some of the examples, additional characterization is performed on the nanoparticulates after they are released from the matrix of the multi-phase particles, including testing the nanoparticulates for luminescense. The results are summarized in Table 17.
The results of the XRD analysis determines that the phases detected correspond to the phases that would be expected based on the processing conditions.
The presence of NaNO3 is clearly indicated in XRD measurements of powders containing multi-phase particles with a high matrix to nanoparticulate ratio. The desired nanoparticulate Na(Y,Yb,Er)F4 phase is always formed. In most cases, the Na(Y,Yb,Er)F4 phase is accompanied by NaYbF4 and/or NaYF4, which may be reacted with NaErF4 at higher temperatures. The NaErF4 concentration is not high enough to be detected by XRD.
The processing of the powders can also be carried out in the presence of exces NaOfAc. During processing, NaOfAc forms an NaF matrix in-situ. The NaF matrix is formed after the water has been removed from the droplets of precursor medium. The use of excess NaOfAc to form a NaF matrix is selected because it provides free fluoride ions in the precursor solution, resulting in precipitation of YF3.
As mentioned above, the precursor mediums are prepared with an excess of HOfAc to ensure a quantitative transformation of the metal carbonate precursors to the corresponding metal trifluoroacetate compounds. During the processing of the precursor mediums, excess HOfAc is converted into HF, which combines with NaF to form NaF.HF as is inferred by the XRD analysis.
SEM photomicrographs show that the multi-phase particles range in size between about 1 μm and 5 μm. The nanoparticulates (the desired phosphor product) range in size between about 50 nm and 200 nm.
Two of the samples are subjected to a step for separating the phosphor nanoparticulates from the matrix. 0.2 grams of powder from sample 1 are suspended in 10 ml water and stirred for 1 min. After settling, the supernatant is decanted. This process is repeated once. The resulting powder, sample 1A, is dried in air at room temperature.
1.1 grams of powder from sample 6 is suspended in 40 ml of water and stirred for 1 min. The salt matrix is dissolved while the Na(Y,Yb,Er)F4 nanoparticulates stay in suspension. After settling, the supernatant is decanted. This process is repeated once. The resulting powder, sample 6A, is dried in air with a heat gun.
The phosphor nanoparticulates from sample 6A are shown to be pure Na(Y,Yb,Er)F4 by XRD. The powder also shows green luminescence when irradiated by an infrared laser. Qualitatively, the brightness of the nanoparticulates of sample 6A is lower than the nanoparticulates of sample 1A.
Spray Pyrolysis Systems Used in Some of Examples 3-23Some of the following Examples utilize a pilot scale spray pyrolysis system. The pilot scale spray pyrolysis system consists of an ultrasonic generator, a tube furnace, and a bag house. An aerosol of a precursor medium is generated in the ultrasonic generator, flowed horizontally through a tube inside the tube furnace, and collected on a filter inside the bag house. The ultrasonic generator consists of a 3×3 array of piezoelectric transducers that are arranged on the base of a generation chamber. The transducers operate in a water bath that sits just below the generator box. The generator box is a separate unit with a sealed polyimide (Kapton) membrane that separates the water bath and the precursor medium. The transducers act upon the precursor medium through this film to generate droplets of the precursor medium. A carrier gas is flowed into the generator box to move the droplets of precursor medium through a hot zone. In most cases, the carrier gas is air, but other gasses such as nitrogen, or forming gas may be employed. The hot zone consists of a quartz tube inside the tube furnace. The tube may be composed of materials such as metals or ceramics. The particles made from the precursor medium are collected in a bag house. Prior to collection, at the end of the hot zone, a quench gas is introduced. The quench gas may be air, nitrogen, forming gas or other gasses. The quench gas helps to lower the bag-house temperature to avoid filter degradation and negative effects associated with particle contact at high temperatures. The particles are collected on a filter and the gas flow is exhausted.
Some of the following Examples utilize a lab scale spray pyrolysis system, which is similar to the pilot scale spray pyrolysis system described above. However, the generator box in the lab scale system uses only one piezo transducer, which is in direct contact with the precursor medium. Carrier gas is run through the generator box into a tube furnace and particles are collected on a disk filter. Unless otherwise noted, the carrier gas is air. The disk filter is heated to avoid moisture precipitation inside the filter holder. There is no quench gas system on the lab scale system.
Example 3 Yttria Nanoparticulates and Salt MatrixA precursor medium containing yttrium nitrate hexahydrate, Y(NO3)3 6H2O and sodium nitrate NaNO3, dissolved in deionized water is prepared. The precursor medium contains:
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- Y(NO3)3*6H2O 85 g
- NaNO3 101.9 g
- H2O 200 g
The precursor medium is sprayed out of a pump spray bottle onto a hotplate. The hotplate has a sheet of foil and a glass plate, onto which the precursor medium is sprayed. The glass plate is at a temperature of 300° C. The resulting deposit is scraped off of the glass plate and is then heated in a porcelain crucible using a box furnace. The box furnace is operated by being ramped up at 15° C./minute to a temperature of 550° C. and held at 550° C. for 12 minutes, then cooled at about 10° C./minute.
After processing the powder, examination indicates that the salt matrix melted during heating in the furnace. Also, some of the salt matrix vaporizes during the thermal treatment in the furnace, but the amount is not quantified. After the powder is thermal treated in the furnace, water is added to the crucible and the combined water and powder is poured onto a watch glass, where it is dried and subjected to characterization using XRD. XRD indicates very crystalline Y2O3. SEM images show that the Y2O3 nanoparticulates have a size in the range of 200 nm and smaller.
Example 4 Yttria Nanoparticulates and Salt MatrixA precursor medium is prepared containing:
-
- Y Nitrate soln 114 g
- Eu Nitrate soln 11.8 g
- NaNO3 88.9 g
- Deionized H2O 1790 g
The precursor medium is processed using a spray dryer run at 232° C. as the inlet temperature and 121° C. for the outlet temperature, to produce a powder of multi-phase particles. Characterization of the powder using XRD indicates the presence of Y(NO3)3.5H2O and NaNO3. The powder may be post treated by heating to produce yttria nanoparticulates from the Y(NO3)3.5H2O.
Example 5 Silver Nanoparticulates and Salt MatrixA precursor medium containing silver nitrate, AgNO3 and sodium nitrate NaNO3, dissolved in deionized water is prepared. The precursor medium contains:
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- AgNO3 10 g
- NaNO3 12.3 g
- Deionized H2O 200.5 g
This precursor medium is designed for 10 wt % loading of salts, and to yield particles consisting of 10 vol % silver metal in a sodium nitrate salt matrix. The precursor medium is processed on the lab scale system described above, at a temperature of 300° C. and a carrier gas flow rate of 5 liters per minute (lpm). XRD analysis of the resulting powder shows strong sodium nitrate (NaNO3) peaks without the presence of silver nitrate or silver peaks.
The precursor medium is also processed on the lab scale system at 400° C. and a carrier gas flow rate of 5 lpm. XRD pattern for this powder again shows strong sodium nitrate peaks. In this case there are also very small peaks that can be correlated to silver. No silver nitrate peaks are present, but silver metal peaks are not strong enough to indicate full decomposition of silver nitrate to silver. The particle may contain amorphous silver nitrate that may be post processed at low temperatures (<300° C.) in a reducing environment to yield nanoparticulates of silver.
Example 6 Silver Nanoparticulates and Salt MatrixA precursor medium containing silver nitrate, AgNO3 and sodium nitrate NaNO3, dissolved in deionized water is prepared. The precursor medium contains:
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- AgNO3 100 g
- NaNO3 123 g
- Deionized H2O 2030 g
The precursor medium is designed to approximate the precursor medium of Example 5. This material is processed with a spray dryer having an inlet temperature of 293° C. and an outlet temperature of 171° C. The powder recovered is light gray-blue in color. XRD of the powder indicates that sodium nitrate is present and also indicates that there may be some copper nitrate hydroxide contamination from previous processing of other precursor mediums. Sodium nitrate is well defined by the XRD but, no silver nitrate peaks are present. Silver nitrate may be amorphous and present in solid solution with the sodium nitrate. The silver nitrate may be converted to silver nanoparticulates by low temperature processing (<300° C.) in a reducing environment.
Example 7 Silver Nanoparticulates and Salt MatrixA precursor medium containing silver nitrate, AgNO3 and strontium nitrate Sr(NO3)2, dissolved in deionized water is prepared. The precursor medium contains:
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- AgNO3 37.5 g
- Sr(NO3)2 60.9 g
- Deionized H2O 557.6 g
The precursor medium is designed to yield a particle that is 10 vol % silver metal in a strontium nitrate salt matrix. Strontium nitrate is chosen for its solubility in water and for having a higher melting temperature than sodium nitrate. Strontium nitrate begins to melt or decompose at approximately 570° C. compared to sodium nitrate, which melts at approximately 330° C.
The precursor medium is processed at 450° C., 500° C., and 550° C. on the pilot scale system, with a carrier gas flow rate of 60 lpm. XRD indicates the presence of silver, strontium nitrate, and silver nitrate to varying degrees at the three temperatures. This indicates that the precursor medium cannot be processed to complete decomposition of silver without a reducing agent in the precursor, or a post process treatment of the powder.
Example 8 Silver Nanoparticulates, Silica and Salt MatrixA precursor medium is prepared containing:
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- AgNO3 10.0 g
- NaNO3 12.3 g
- Aerosil 200 (silica) 1.3 g
- Deionized H2O 212.8 g
This precursor medium is designed for 10 wt % loading of salts plus a fumed silica (with a surface area of 200 m2/g), and is designed to yield 10 vol % silver metal, approximately 10 vol % silica and 80 vol % sodium nitrate matrix. The precursor medium is processed using the lab scale spray pyrolysis system previously described. The precursor medium is processed at 300° C. and 400° C., with a carrier gas flow rate of 5 lpm. The powders made from the precursor are pink-tan for the precursor medium processed at 300° C. and gray-brown for the precursor medium processed at 400° C. Characterization of the powders using XRD indicates the presence of NaNO3 but not crystalline AgNO3. The AgNO3 may be amorphous. Additionally, the XRD does appear to indicate the presence of a small amount of converted silver. This powder may be post treated by heating in a reducing environment to form silver nanoparticulates from the amorphous AgNO3.
Example 9 Silver Nanoparticulates, Silica and Salt MatrixA precursor medium is prepared containing:
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- AgNO3 100.3 g
- NaNO3 123.4 g
- Aerosil 200 (silica) 13.4 g
- Deionized H2O 2135 g
The precursor is prepared to contain the same ratios of components as Example 8. The precursor medium is processed using a spray dryer with an inlet temperature of 293° C. and outlet temperature of 171° C. The resulting powder is gray in color. The XRD analysis of the powder shows strong sodium nitrate peaks and no silver or silver nitrate peaks. This powder may be post treated by heating in a reducing environment to form silver nanoparticulates from the amorphous AgNO3.
Example 10 Silver Nanoparticulates and Salt Matrix with Use of Reducing AgentA precursor medium is prepared containing:
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- AgNO3 10.0 g
- NaNO3 12.3 g
- Deionized H2O 212.8 g
- 3-amino-1-propanol 13.0 g
The precursor medium is processed on the lab scale system at 400° C. Due to problems with buildup of system pressure, 450° C. is chosen as the temperature with a carrier gas flow rate of 5 lpm. The resulting powder is brown in color. XRD indicates the presence of sodium nitrate and silver.
Example 11 Silver Nanoparticulates, Silica and Salt Matrix with Use of Reducing AgentA precursor medium is prepared containing:
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- AgNO3 10.0 g
- NaNO3 12.3 g
- Aerosil 200 (silica) 1.3 g
- Deionized H2O 212.8 g
- 3-amino-1-propanol 13.0 g
This precursor medium is designed for 10 wt % loading of salts plus a fumed silica (with a surface area of 200 m2/g) and is designed to yield 10 vol % silver metal, approximately 10 vol % silica and 80 vol % sodium nitrate matrix. Additionally, the precursor medium contains a reducing agent for creating a reducing environment for converting the AgNO3 to silver.
The precursor medium is processed using the lab scale spray pyrolysis system at temperatures of 350° C., 400° C. and 450° C., with a carrier gas flow rate of 5 lpm. The spray pyrolysis system runs well at 400° C. and 450° C. but the filter clogs at 350° C. giving a small sample. The powder produced from the processing is very dark brown.
Characterization of the powder produced from processing at 350° C. indicates the presence of NaNO3 and cubic silver. The powders produced at 400° C. and 450° C. also indicate the presence of NaNO3 and cubic silver, but show an unidentified crystalline phase having more pronounced peaks at 450° C. than at 400° C. Transmission electron microscope (TEM) images are taken of the sample processed at 350° C. The TEM images show silver nanoparticulates of about 20 nm in a matrix, with some of the nanoparticulates as small as 5 nm. The TEM beam seems to melt the sodium nitrate matrix. Silica may be present in some instances as a matrix but it is unclear if the silica is present at the surface of the nanoparticulates to form a coating.
Example 12 Silver Nanoparticulates, Silica and Salt Matrix with Use of Reducing AgentA precursor medium is prepared containing:
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- AgNO3 100.2 g
- NaNO3 123.4 g
- Aerosil 200 (silica) 13.4 g
- Deionized H2O 2125 g
- 3-amino-1-propanol 100 g
The precursor has the same silver/silica/sodium nitrate ratios as in Example 11, with a slightly lower 3-amino-1-propanol ratio. The above precursor is prepared and shipped overnight for processing in a spray dryer. This is different from the precursor mediums processed on the pilot scale and lab scale spray pyrolysis systems, which are processed immediately after preparation. The precursor material ages during shipping to the spray dryer. When initially mixed, the material is clear and light yellow in color. After shipping the material is still clear, but is gray in color, and some settling of the silica component appears to take place. The precursor medium is stirred to resuspend the silica and processed through the spray dryer with an inlet temperature of 482° C. and an outlet temperature of 260° C. The recovered powder is dark gray-brown in color. The XRD pattern of this material shows strong silver peaks as well as sodium nitrate peaks.
The above material is post processed to separate the silver-silica particles. This is done by solvating the sodium nitrate matrix with deionized water and separating the silver-silica particles from the slurry by centrifuge. Particles are collected as a cake, then resuspended and centrifuged several times in order to remove all the sodium nitrate. In the last step, particles are suspended in absolute ethanol and allowed to dry in a crystallization dish at 60° C. The recovered powder is analyzed by XRD, SEM and BET. XRD indicates silver with no sodium nitrate remaining. Crystallite size is calculated, by the Scherer equation, as 21.3 nm. SEM of the material indicates particles in the sub100 nm range.
Example 13 Silver Nanoparticulates, Silica and Salt Matrix with Use of Reducing AgentA precursor medium similar to the one in Example 12 is prepared containing:
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- AgNO3 37.5 g
- NaNO3 46.2 g
- Aerosil 200 (silica) 5.0 g
- Deionized H2O 742 g
- 3-amino-1-propanol 56.2 g
The precursor medium is processed using the pilot scale system at 450° C., 500° C. and 550° C. with a carrier gas flow rate of 60 lpm. XRD of the collected powders indicate the presence of silver and sodium nitrate. The sample produced at 450° C. is separated from the matrix with deionized water in a test tube and analyzed by XRD. The XRD indicates the presence of silver. Calculation of the crystallite size via the Scherer equation gives 16 nm.
Larger amounts of the sample produced at 450° C. are separated from the salt matrix by addition of water and centrifugation. This is done 3 times, after which the separated material is dispersed in methanol and dried in air at room temp until most of the methanol is gone. The separated material is then dried at 120° C. in a box oven for one hour. BET surface area for this material is measured to be 33.7 m2/g.
SEM of all powders show particles on the order of 1 to 5 microns with smaller silver particulates present on the surface. All the powders seem to produce silver inclusions ranging from 50 nm to 200 nm. The samples made at higher temperatures seem to be dryer and easier to handle.
Collection and separation of the powders is complicated by the presence of organic residue. This residue imparts an orange hue when the powders are put into water. This residue is also present on the inside of the bag housing after the precursor medium is processed. It is assumed that the residue may be formed due to the presence of the 3-amino-1-propanol reducing agent.
Example 14 Silver Nanoparticulates, Silica and Salt Matrix with Use of Reducing AgentA precursor medium is prepared containing:
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- AgNO3 5 g
- NaNO3 6.2 g
- Sol-gel solution 13.4 g
- Deionized H2O 94 g
- 3-amino-1-propanol 7.5 g
The precursor medium contains a premixed sol-gel solution composed of tetraethoxysilane, ethanol, water, and a catalyst and yields about 28.8 wt % silica. The sol-gel solution is used in place of the Aerosil 200 fumed silica used in previous Examples. The precursor medium is designed to yield the same ratios of components as Examples 11-13, with particles of 80 vol % sodium nitrate, 10 vol % silica, and 10 vol % silver. This material is processed using the lab scale system at 450° C., with a carrier gas flow rate of 5 lpm. The SEM images of the resulting powder shows silver particles ranging from 50 to 500 nm inside micron size matrix particles. This precursor produces silver particles that are much larger than those generated with precursor mediums that have fumed silica.
Example 15 Silver Nanoparticulates, Silica and Salt Matrix with Use of Reducing AgentA precursor medium is prepared containing:
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- AgNO3 15 g
- NaNO3 18.6 g
- 3-aminopropyl triethoxysilane 13.4 g
- 3-amino-1-propanol 9.0 g
- Ethanol 33.5 g
- Deionized H2O 301.8 g
In the precursor medium, 3-aminopropyl triethoxysilane is used as both reducing agent and silica precursor. 3-amino-1-propanol is also used in order to maintain a similar silica volume ratio to the previous Examples (that have silica, silver, salt and a reducing agent), while ensuring that the silver is completely complexed. Ethanol is used as a medium to combine the two reducing agents while minimizing the chance of gel formation. The precursor medium is mixed by first making an aqueous solution of the nitrates (AgNO3 and NaNO3) and then a mixture of 3-amino-1-propanol and 3-aminopropyl triethoxysilane in ethanol. The two solutions are combined to yield a clear light brown precursor medium. The precursor medium is allowed to sit for 30 minutes to an hour to ensure no gel formation. The precursor medium is then processed using the pilot scale system at 450° C. with a carrier gas flow rate of 60 lpm.
XRD of the resulting powder indicates the presence of silver and sodium nitrate. SEM images of the powder show silver particles on the order of 100 nm inside micron size matrix particles. Some areas show particles that are smaller; on the order of 50 nm. Overall, the powders appear to be comparable to those produced with fumed silica.
Example 16 Silver Nanoparticulates, Silica and Salt Matrix with Use of Reducing AgentA precursor medium is prepared containing:
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- AgNO3 37.5 g
- NaNO3 46.1 g
- Aerosil 200 fumed silica 5.1 g
- Ethylene Diamene 22.5 g
- Deionized H2O 776 g
The precusor medium is prepared with ethylenediamene as a reducing agent instead of 3-amino-1-propanol. The precursor medium is processed using the pilot scale system at a temperature of 550° C. and a carrier gas flow rate of 60 lpm. XRD of the powders indicates the presence of sodium nitrate and silver. SEM images of the powders appear very similar to those produced with 3-amino-1-propanol as the reducing agent. The residue associated with the powders made from precursor mediums containing 3-amino-1-propanol as a reducing agent (see Example 13) is not present in the baghouse.
Example 17 Silver Nanoparticulates, Polymer and Salt Matrix with Use of Reducing AgentA precursor medium is prepared containing:
-
- AgNO3 5 g
- NaNO3 6.3 g
- 3-amino-1-propanol 7.5 g
- Polyvinyl pyrrolidone 10,000 MW 0.5 g
- Deionized H2O 94 g
The precursor medium is processed using the lab scale system at 450° C. with a carrier gas flow rate of 5 lpm. XRD of the powder shows silver but no indication of sodium nitrate peaks. This may be due to the presence of the polyvinyl pyrrolidone (PVP) polymer. SEM images of the powder show silver particles in a matrix. The silver particles appear to have a structure similar to strings of necked particles. The strings appear to be on the order of 1 to 2 microns in length within matrix particles around 1 to 3 microns in diameter.
Example 18 Silver Nanoparticulates, Polymer and Salt Matrix with Use of Reducing AgentA precursor medium is prepared containing:
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- AgNO3 75 g
- NaNO3 92.2 g
- Ethylene diamene 45 g
- Polyvinyl pyrrolidone 10,000 MW 15 g
- Deionized H2O 1640 g
The precursor medium is a modification of Example 17, which is processed using the lab scale system. The precursor medium is designed to have a loading of 10 wt % of soluble materials. The amount of PVP is roughly doubled, with respect to other components, as compared to the precursor medium in Example 17. This should produce particles that are about 7.7 vol % silver, 24.8 vol % PVP and 67.5 vol % sodium nitrate. The precursor medium is processed using the pilot scale system at 550° C. and with a carrier gas flow rate of 60 lpm.
The powder is dark gray in color. XRD of the powder indicates peaks for silver and sodium nitrate. SEM images of the powder look very different from Example 17, made with half as much PVP in the precursor medium. Many of the multi-phase particles appear to have nanoparticulates on the order of 100 nm uniformly coating the surface of the micron sized multi-phase particles. Other multi-phase particles within the same lot have a much different microstructure-containing a silver component at the surface that is much more aggregated, and which are not distributed uniformly throughout the multi-phase particle. Many of the multi-phase particles appear to have these silver aggregate particulates present on only one side of the particle.
The precursor medium is also processed at lower temperatures of 400° C., 450° C., and 500° C. and at a higher temperature of 600° C. These temperature variations seem to have little effect upon particle morphology as determined by SEM, but the temperatures of 500° C. and lower consistently clog the filter bags on the pilot scale system.
Separation of the nanoparticulates from the multi-phase particles is attempted by addition of water to the powder. About 0.2 to 2 g of different powders are mixed with about 50 g of water. This produces a light gray-green suspension for powders processed at 550° C. Powders processed at 500° C. and 450° C. tend to form dark brown suspensions. Nanoparticulates are separated by flocculation overnight or by centrifugation at 700 rpm. The color of the water after settling of the nanoparticulates varies from light yellow for powders processed at 550° C. to dark yellow to orange for powders processed at 500° C. and 450° C.
After settling of the nanoparticulates, they can be resuspended in a small amount of ethylene glycol but are not stable for more than several minutes. Films made from drying the settled nanoparticulats on a hotplate, at 120° C., appear to be thin and uniform. Deposits are gray in color, but have areas that are shiny. It is assumed that the darker areas are larger particles and that shiny areas may be the result of smaller particles.
Example 19 Silver Nanoparticulates and Silica Matrix with Use of Reducing AgentA precursor medium is prepared containing:
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- AgNO3 10.0 g
- Aerosil 200 (silica) 1.3 g
- Deionized H2O 89.0 g
- 3-amino-1-propanol 13.0 g
The precursor medium is made by mixing a 20 wt % silver nitrate in water solution. Aerosil 200 fumed silica is added to the solution and suspended with an ultrasonic horn. A 3-amino-1-propanol solution is then prepared separately and the two mixtures are combined to produce a slightly opaque yellow mixture. The precursor is designed to yield particles with a one to one ratio of silver and silica.
The precursor medium is processed using the lab scale system at 450° C., with a carrier gas flow rate of 5 lpm. The collected powder is dark gray. XRD of the powder shows peaks for silver. SEM shows particles on the order of 1 micron in size that appear to be composed of smaller particles in the range of 50 to 200 nm.
Example 20 Silver Nanoparticulates and Polymer MatrixA precursor medium is prepared containing:
-
- AgNO3 30 g
- Polyvinyl pyrrolidone 10,000 MW 12 g
- Deionized H2O 235 g
The precursor medium has 15 wt % soluble components and is designed to yield particles with 13.4 vol % silver nanoparticulates inside a PVP matrix. The precursor medium is formulated with the idea of achieving similar results as have been achieved by liquid batch routes in the polyol process, which produces silver nanoparticulates of approximately 50 nm in size.
The precursor medium is processed using the pilot scale system at 550° C. with a carrier gas flow rate of 60 lpm. The resulting powder is very dark brown. XRD of the resulting powder indicates contamination of strontium nitrate from a previous precursor medium, but primarily shows the presence of silver. Some silver nitrate appears to be present, but is difficult to identify. SEM images of the powder show spherical particles on the order of 1 to 5 microns. The surface of the spherical particles appears to contain nanoparticulates. The larger particles contain features less than 100 nm in diameter on their surfaces. Some of the larger particles appear to be hollow and the nanoparticulates can be seen in pieces of crumbled micron size hollow particles.
The precursor medium is also processed using the pilot scale system at 350° C. with a carrier gas flow rate of 60 lpm. XRD of this sample is also contaminated with strontium nitrate from previously processed precursor mediums, but does clearly show the presence of silver. The morphology of the powder is similar to the powder produced at 550° C., with sub-100 nm features visible on the surface of micron size particles.
Example 21 Copper Nanoparticulates and Salt MatrixA precursor medium is prepared containing:
-
- Cu(NO3)2 3H2O 7.7 g
- NaNO3 13.6 g
- Deionized H2O 176.6 g
The precursor medium has a loading of 10 wt % salts and is designed for the copper yield to represent 10 vol % of the powder produced. The precursor medium is processed using the lab scale spray pyrolysis system, with a carrier gas flow rate of 5 lpm. Initially, the precursor medium is processed at a temperature of 250° C., however the powder produced is wet and forms a cake on the filter. The powder on the filter is brown in places and light blue in places. When collected and put in a bottle the overall color is brown. Characterization by XRD indicates the presence of sodium nitrate and copper nitrate hydroxide (Cu4(NO3)2(OH)6 with an unaccounted for peak at 2 theta=45. Additionally, the precursor medium is also processed at 300° C. and 400° C. The increase in temperature produces a drier, slightly darker powder but does not change the XRD pattern.
Example 22 Copper Nanoparticulates and Salt MatrixA precursor medium is prepared containing:
-
- CuNO3*3H2O 200.1 g
- NaNO3 120 g
- Deionized H2O 2874 g
The precursor medium is mixed and packaged in liquid form, shipped, and processed in a spray dryer. The precursor medium is processed at an inlet temperature of 282° C. and an outlet temperature of 149° C. The liquid production rate of this sample is about 300 g/minute. About 100 grams of powder are collected. The powder is light blue-green in color. XRD of the powder indicates the presence of sodium nitrate (NaNO3) and copper nitrate hydroxide (Cu4(NO3)2(OH)6. The powder must be post treated in a reducing atmosphere in order to reduce the copper nitrate hydroxide to copper nanoparticulates.
Example 23 Copper Nanoparticulates, Silica and Salt MatrixA precursor is prepared by dissolving salts in water in combination with fumed silica particles. The precursor medium contains:
-
- CuNO3*3H2O 200 g
- NaNO3 119.2 g Aerosil 200 fumed silica 13 g H2O 2885 g
The precursor medium has a loading of 10 wt % salts and is designed for the copper yield to represent 10 vol % of multi-phase particle assuming complete conversion of the copper precursor to copper with 10 vol % silica and 80 vol % NaNO3. The precursor medium is mixed and packaged in liquid form, shipped, and processed in a spray dryer. The precursor medium is processed in the spray dryer with an inlet temperature of 293° C. and an outlet temperature of 171° C. The powder is light blue-green in color. XRD indicates the presence of NaNO3 and copper nitrate hydroxide Cu4(NO3)2(OH)6. The powder may be post treated by heating to form silica with copper oxide nanoparticulates in a salt matrix.
Example 24 Precursor Mediums with Silver Nitrate and High Melting Point SaltIn searching, for a salt matrix material that is stable at high processing temperatures, salts such as fluorides, chlorides and sulfates are considered. However, these system have a propensity to form insoluble silver salts with the chloride and fluoride ions in solution, which also cause corrosion of processing equipment. A solution to this problem is achieved by complexing the silver from the silver nitrate with an amine such as 3-amino-1-propanol.
In one case, silver nitrate is combined with sodium sulfate in water in an attempt to create an aqueous precursor medium. Silver sulfate precipitates as a result. The problem is resolved by complexing the silver with 3-amino-1-propanol, which results in a clear gray-green solution, when 3-amino-1-propanol is added to the precursor medium in greater than a 2 to 1 molar ratio to silver.
The foregoing discussion of the invention has been presented for purposes of illustration and description. The foregoing is not intended to limit the invention to only the form or forms specifically disclosed herein. Although the description of the invention has included description of one or more embodiments and certain implementations, variations and modifications, other implementations, variations and modifications are within the scope of the invention, e.g., as may be within the skill and knowledge of those in the art after understanding the present disclosure. It is intended to obtain rights which include alternative embodiments to the extent permitted, including alternate, interchangeable and/or equivalent structures, functions, ranges or steps to those claimed, whether or not such alternate, interchangeable and/or equivalent structures, functions, ranges or steps are disclosed herein, and without intending to publicly dedicate any patentable subject matter. Furthermore, any feature described with respect to any disclosed embodiment, implementation or variation of any aspect of the invention may be combined in any combination with one or more features of any other embodiment, implementation or variation of the same or any other aspect of the invention. For example, additional processing steps can be included at any point before, during or after processing disclosed in any of the process embodiments described herein or shown in any of the figures, so long as the additional steps are not incompatible with the disclosed processing according to the present invention. Moreover, processing steps disclosed in any of the process embodiments described herein can be combined with any other processing steps described with any other process embodiment. Not to limit the generality of the foregoing, any number of the decomposing particles 116, modifying nanoparticulates 118, modifying matrix 126, separating nanoparticulates 128, dispersing nanopaticulates 130, collecting particles 136, quenching particles 144, treating particles 146 and removing solutes 148 may be combined, with or without the generating gas dispersion 102 and/or the forming particles 104, in any way provided that the combination is not technically incompatible, and all such combinations are within the scope of the present invention.
The terms “comprising, “containing, “including, and “having,” and variations thereof, are intended to be non-limiting in that the use of such terms indicates the presence of some condition or feature, but not to the exclusion of the presence of any other condition or feature. Percentages stated herein are by weight unless otherwise expressly stated.
Claims
1. A gas dispersion method for making nanoparticulates, the method comprising:
- generating a flowing gas dispersion, as generated the gas dispersion comprising droplets of a precursor medium dispersed in a gas phase, with the precursor medium comprising liquid vehicle and at least two precursors, a first said precursor being a precursor to a first material and a second said precursor being a precursor to a second material;
- in the gas dispersion, forming multi-phase particles dispersed in the gas phase, the multi-phase particles each comprising a dispersion of nanoparticulates and matrix, with the nanoparticulates maintained in a dispersed state in the multi-phase particles by the matrix;
- the forming multi-phase particles comprising removing at least a portion of the liquid vehicle from the droplets to the gas phase and forming the matrix and the dispersion of the nanoparticulates, with the nanoparticulates comprising the first material and the matrix comprising the second material; and
- wherein during the forming, average stream temperature of the gas dispersion does not exceed a melting temperature of the matrix for longer than 10 seconds.
2. The method of claim 1, wherein during the forming, the average stream temperature of the gas dispersion is maintained at lower than the melting temperature of the second material.
3. The method of claim 1, wherein during the removing, the average stream temperature of the gas dispersion does not exceed a temperature that is at least 10° C. lower than the melting temperature of the second material.
4. The method of claim 1, wherein the second material has a melting temperature of at least as high as 100° C.
5. The method of claim 1, wherein the second material has a melting temperature in a range of from 100° C. to 500° C.
6. The method of claim 1, wherein during the forming, the average stream temperature of the gas dispersion does not exceed a melting temperature of the matrix for longer than 5 seconds.
7. The method of claim 1, wherein during the forming, the average stream temperature of the gas dispersion does not exceed a melting temperature of the second material by more than 100° C.
8.-23. (canceled)
24. A gas dispersion method for making nanoparticulates, the method comprising:
- generating a flowing gas dispersion, as generated the gas dispersion comprising droplets of a precursor medium dispersed in a gas phase, with the precursor medium comprising liquid vehicle and at least two precursors, a first said precursor being a precursor to a first material and a second said precursor being a precursor to a second material;
- in the gas dispersion, forming multi-phase particles dispersed in the gas phase, the multi-phase particles each comprising a dispersion of nanoparticulates and matrix, with the nanoparticulates maintained in a dispersed state by the matrix;
- the forming multi-phase particles comprising removing at least a portion of the liquid vehicle from the droplets to the gas phase and forming the matrix and the dispersion of the nanoparticulates, with the nanoparticulates comprising the first material and the matrix comprising the second material; and
- after the forming multi-phase particles, treating the multi-phase particles to modify at least one of the nanoparticulates and the matrix while the nanoparticulates are in the dispersed state.
25. The method of claim 24, wherein the treating is performed while the multi-phase particles are dispersed in the gas phase.
26. (canceled)
27. The method of claim 24, wherein prior to the treating, separating the multi-phase particles from the gas phase.
28. The method of claim 27, wherein the gas dispersion is the first gas dispersion and the method comprises, after the separating and prior to the treating:
- dispersing the multi-phase particles in a carrier gas to form a second gas dispersion and performing the treating in the second gas dispersion.
29.-62. (canceled)
63. A method for modifying a chemical or physical property of nanoparticulates, the method comprising:
- maintaining the nanoparticulates in a dispersed state within multi-phase particles comprising the nanoparticulates and matrix; and
- during the maintaining, treating the nanoparticulates, wherein the treating comprises modifying at least one property of the nanoparticulates to prepare modified nanoparticles.
64. The method of claim 63, wherein the treating comprises subjecting the multi-phase particles to a thermal treatment at elevated temperature.
65. The method of claim 63, wherein the modifying comprises structural modification of the nanoparticulates during the thermal treatment.
66. The method of claim 63, wherein the modifying comprises compositional modification of the nanoparticulates during the thermo treatment.
67.-99. (canceled)
100. A method for making multi-phase particles comprising nanoparticulates and matrix, the method comprising:
- generating a flowing gas dispersion, as generated the gas dispersion comprising droplets of a precursor medium dispersed in a gas phase, with the precursor medium comprising liquid vehicle and at least two precursors, a first said precursor being a precursor to a first material and a second said precursor being a precursor to a second material;
- in the gas dispersion, removing at least a portion of the liquid vehicle from the droplets to the gas phase and forming first particles dispersed in the gas phase;
- modifying the first particles to form second particles, the second particles being multi-phase particles each comprising a dispersion of nanoparticulates and matrix, with the nanoparticulates maintained in a dispersed state in the multi-phase particles by the matrix; and
- wherein the nanoparticulates comprise the first material and the matrix comprises the second material.
101.-102. (canceled)
103. The method of claim 100, wherein the first particles comprise nanoparticulate domains and the modifying comprises increasing the size of the nanoparticulate domains to form the nanoparticulates.
104. The method of claim 100, wherein the first particles do not comprise nanoparticulate domains and the modifying comprises forming the nanoparticulates.
105. The method of claim 100, wherein the first particles comprise unreacted first precursor and the modifying comprises reacting at least a portion of the unreacted first precursor to form the first material.
106.-124. (canceled)
Type: Application
Filed: Aug 8, 2005
Publication Date: Aug 2, 2007
Applicant: CABOT CORPORATION (Boston, MA)
Inventors: Toivo Kodas (Albuquerque, NM), Mark Hampden-Smith (Albuquerque, NM), Klaus Kunze (Albuquerque, NM), David Dericotte (Albuquerque, NM), Karel Vanheusden (Placitas, NM), Aaron Stump (Albuquerque, NM)
Application Number: 11/199,512
International Classification: A61K 9/14 (20060101); B29B 9/00 (20060101);
