MAGNETIC NANOPARTICLES, BULK NANOCOMPOSITE MAGNETS, AND PRODUCTION THEREOF
Provided herein are systems, methods, and compositions for magnetic nanoparticles and bulk nanocomposite magnets.
Latest Board of Regents, The University of Texas System Patents:
This application claims priority to U.S. provisional application Ser. No. 61/016,353, filed Dec. 21, 2007, incorporated by reference herein.GOVERNMENT RIGHTS STATEMENT
This invention is made under Government support DoD/MURI under Grant No. N00014-05-1-0497 and DoD/DARPA through ARO under Grant No. DAAD-19-03-1-0038. The U.S. Government may have certain rights to this invention.BACKGROUND OF THE INVENTION
The present invention relates generally to magnetic nanoparticles and more particularly to bulk magnetic nanocomposites.
The size distribution of nanoparticles obtained by ball milling can be wide compared with chemical synthesis methods. Chemical synthesis methods have limited success in the synthesis of hard magnetic nanoparticles of rare-earth compounds.
The grain size in nanocomposite magnets fabricated by conventional top-down methods, including mechanical alloying and rapid quenching, usually has a wide distribution, and can hardly be controlled below the critical length. Fabrication of high density bulks with controlled grain size and grain alignment of the hard magnetic phases remains challenging. An alternative bottom-up approach fabricates nanocomposite magnets with controllable nanoscale morphology. The embodiments disclosed herein solves these problems, as well as others.SUMMARY OF THE INVENTION
Provided herein are systems, methods and compositions for magnetic nanoparticles and bulk nanocomposite magnets.
The methods, systems, and compositions are set forth in part in the description which follows, and in part will be obvious from the description, or can be learned by practice of the methods, compositions, and systems. The advantages of the methods, compositions, and systems will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the methods, compositions, and systems, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate aspects of the methods, compositions, and systems and together with the description, serve to explain the principles of the methods, compositions, and systems.
The methods, compositions, and systems can be understood more readily by reference to the following detailed description of the methods, compositions, and systems and the Examples included therein and to the Figures and their previous and following description.
The term “nanoparticles” includes particles having an average size between about 2 and about 100 nm, preferably particles having an average size between about 2 and about 100 nm. Most preferably, the nanoparticles have an average size between about 2 and about 10 nm. The term “nanocomposites” includes composites including more than one nanoparticle.
Generally speaking, a bulk nanocomposite magnet 10 comprises at least one hard magnetic phase material 12 and at least one soft magnetic phase material 14, as shown in
Interphase exchange coupling is enhanced upon the compaction of the hard and soft phase material. Effective interphase magnetic exchange coupling in the bulk nanocomposite is achieved by limiting the dimensions of the soft phase material to a nanoscale critical length, as determined by Zambano et al. “Dependence of Exchange Coupling Interaction on Micromagnetic Constants in Hard/soft Magnetic Bilayer Systems”, Physical Review B, 75: 144429-1-7 (2007), herein incorporated by reference. In one embodiment, post-annealing the bulk nanocomposite 10 under a forming gas at an elevated temperature to improve the magnetic performance of the bulk nanocomposite 10 owing to interface modification. Additionally, grain growth and grain size is controlled with warm compaction by selecting P-T-t profiles to ensure chemical stability of the magnetic nanoparticles. The bulk nanocomposite includes a controlled grain size for intergrain magnetic exchange coupling and high energy products.
“Bulk” is a term used in the application to mean any nanocomposite magnet having a dimension of at least about 0.5×0.5×0.5 mm, preferably at least about 1×1×1 mm, most preferably at least about 3×1.2×0.5 mm, alternatively between 6×1.5×0.5 mm. “Bulk nanocomposite” is also referred to as a “compact”. The bulk nanocomposite 10 may include a general three dimensional shape including a rectangular shape, cubical, cuboidal, cylindrical, polyhedronal, and the like. The “soft phase material” 14 comprises at least one of FeO, Fe2O3, Fe3O4, Co, Fe, Ni, CoFe, NiFe, CoO, NiO and other related oxides including doped ferrites including, but not limited to MFe2O3 where M comprises one of Co and Ni. The “hard phase material” 12 comprises at least one of FePt, CoPt, SmCo-based alloys, including SmCO5, Sm2CO17, Sm2CO7, and SmCO7, and rare earth-FeB-based alloys, including R2Fe14B, where R=Nd or Pr, i.e. Nd—FeB and Pr—FeB. The hard phase material and the soft phase material may be mixed pre-warm compaction at a mass ratio of 10:1 to about 5:1, alternatively about 8:1 to about 2:1, alternatively about 1:1. The mass ratio used for mixing the hard and soft phase material depends on the hard and soft phase material selected for warm compaction.
For nanoparticles, the limit for density (“ρp”) of a randomly packed nanoparticle system is only 64% if no deformation is involved. To obtain a higher ρp, plastic deformation of the particles is necessary and is obtained in the warm compaction process. For nanoparticles, the deformation is not as easy as for large nanoparticles because of the reduced dislocations in the nanoparticles, and a lower density values obtained in large nanoparticles warm compacted into a bulk nanocomposite. The bulk samples ρp is dependent on the compaction temperature (“Tcp”) under different pressures. The density of the bulk composite increases monotonously with compaction temperature.
In one embodiment, the bulk nanocomposite magnets are prepared by warm compacting hard phase and soft phase magnetic nanoparticles and/or nanocomposite particles. Generally speaking, the warm compaction apparatus 20 is shown in
The hard and soft phase material may comprise magnetic nanoparticles. The magnetic nanoparticles may include varied characteristics to enhance the magnetic properties of the bulk nanocomposite 10. For example, the magnetic nanoparticle microstructure or morphology may include, but is not limited to, a specific size, such as spherical, aspherical, elongated nanorods, bricklike, wire, cube, hexagonal and tetragonal structures, plate-like structures, monodisperse, polycrystalline, monocrystalline, a specific grain size, and shell of a non-magnetic, antiferromagnetic, or ferro/ferri-magnetic shell, which is otherwise known as a core/shell. The magnetic characteristics may include, but are not limited to, a specific coercivity, magnetocrystalline anisotropy, unsaturated loops, superparamagnetic, ferromagnetic, low or high remanence ratio, single phase-like magnetization, amorphous structure, and exchange coupling.
In one embodiment, the hard phase material may comprise a plurality of FePt nanoparticles with fcc structure, fct structure, or Ll0-phase structure. In another embodiment, the hard and soft phase material may comprise amorphous or crystallized powders.
The magnetic nanoparticles may be modified pre-warm compaction to obtain the magnetic characteristics or microstructures, such as by a heating, annealing, or a ball milling step. In one pre-warm compaction step, the ball milling step may include a gas or a liquid as the media for ball milling for the microstructure or morphology. In one embodiment, the pre-warm compaction step includes synthesizing the particles (nano or micro) and mixing the hard and soft phase particles by ball milling (with a gas or liquid as the media) to form the required nanocomposite morphology. Magnetic nanoparticles may be synthesized or modified by any known method to obtain magnetic characteristics or microstructure, none which are intended to limit the scope of the bulk nanocomposite magnets prepared by warm compaction, some of which are described below.
In one embodiment, the magnetic nanoparticles are synthesized by an airless chemical solution procedure otherwise known as chemical reduction/thermal decomposition. The hard phase and soft phase magnetic nanoparticle material may be synthesized by this method. One example of the standard airless technique uses an argon atmosphere and 0.5 mmol of platinum acetylacetonate (“Pt(acac)2”) is added to 125 mL flask containing a magnetic stir bar and mixed with 20 mL of octyl/benzyl ether, as disclosed in Nandwana et al. “Size and Shape Control of Monodisperse FePt Nanoparticles” J. Phys. Chem. C, 111: 4185-4189 (2007), herein incorporated by reference. After purging with argon for 30 min at room temperature, the flask is heated up to 120° C. for 10 min and a designated amount of oleic acid and oleylamine is added. Iron pentacarbonyl (“Fe(CO)5”) or iron acetylacetonate (“Fe(acac)3”) is used as an iron precursor. Iron acetylacetonate (0.5 mmol) is added at room temperature while iron pentacarbonyl (1.0 mmol) is added at 120° C. when the platinum precursor dissolved completely. The dissolution of Pt(acac)2 in solvent could be followed experimentally by the change of color of the solution from off yellow to transparent yellow. After the addition of Fe(CO)5, the color transition from golden to black suggested formation of nanoparticles in the solution. Then it is heated to 298° C. for 1 h before cooling to room temperature under the argon blanket. Argon gas is flowed throughout the experiment. The heating rate is varied from 1 to 15° C. per minute according to the experimental design.
The black product is precipitated by adding ethanol and separated by centrifugation and redispersed in hexane. To achieve the highest purity, extra ethanol is added in this dispersion and the dispersion is centrifuged again. Because all the particles are quite homogeneous, size selection is not necessary. After washing the particles in ethanol three or more times, they are dispersed in hexane and stored in glass bottles under refrigeration. Samples for magnetic characterization are prepared by depositing a drop of the final hexane dispersion on a 3×3 mm silicon substrate, evaporating the solvent at room temperature and further drying in vacuum, which led to the formation of FePt nanoparticle-assembled thin films. The samples are then annealed at 650° C. for 1 h under the flow of forming gas (Ar+7% H2) in a tube furnace.
Fine-tuning of the sizes of the FePt nanoparticles between 2 and 9 nm may be achieved by controlling the surfactant to metal ratio and the heating rate, as disclosed in Nandwana et al. “Size and Shape Control of Monodisperse FePt Nanoparticles” J. Phys. Chem. C, 111: 4185-4189 (2007), herein incorporated by reference. As shown in
Samples for magnetic measurements are prepared by embedding the nanoparticles in epoxy inside the glove box. Magnetic measurements at room temperature are performed using an alternating gradient magnetometer with measuring field up to 14 kOe, and at 5 K using a superconducting quantum interference device (“SQUID”) with measuring field up to 70 kOe. Structural and morphological characterizations are performed using transmission electron microscope (“TEM”), and x-ray diffractometer (“XRD”). Compositional characterizations are performed using energy dispersive x-ray spectroscopy (“EDX”) and inductively coupled plasma (“ICP”).
In another embodiment, the magnetic nanoparticles are produced by a polyol process. The use of a diol or polyalcohol (for example, ethylene glycol) to reduce metal salts to metal particles is also referred to as the “polyol process”. By mixing and heating both an iron salt and a platinum salt with the polyol, high-quality FePt nanoparticles can be produced. Alternatively, monodisperse SmCO5 nanoparticles are synthesized by coupling the polyol reduction of samarium acetylatacetonate, (“Sm(acac)3”), with the thermal decomposition of CO2(CO)8. For FePt, a slight modification of the decomposition/reduction condition by replacing Fe(CO)5 with Fe(acac)2 or Fe(acac)3 leads to monodisperse 2-3 nm diameter FePt nanoparticles. The stronger organic reducing agent hydrazine (N2H4) may be used to reduce metal salts and form FePt nanoparticle in water at low temperature. In this synthesis, H2PtCl6.H2O and FeCl2.H2O, together with hydrazine and a surfactant, such as sodium dodecyl sulfate (“SDS”) or cetyltrimethylammonium bromide (“CTAB”), are mixed in water. The hydrazine reduces the metal cations at 70° C., resulting in fcc-structured FePt nanoparticles. One example of a modified polyol process is disclosed in Elkins et al “A Novel Approach to Synthesis of FePt Magnetic Nanoparticles” Journal of Nano Research, 1: 23-29 (2008), herein incorporated by reference. The modified polyol process includes Pt(acac)2 and Fe(acac)3 in the molar ratio 1:1 is taken in a 125 mL flask containing a PTFE coated magnetic stir bar at room temperature. 1, 2-hexadecanediol (5 times mole amount of Pt(acac)2 and Fe(acac)3) is added to the flask. 30 mL of dioctyl ether is then transferred into the flask and the contents are stirred while purging with Ar for 30 mins. at room temperature. The flask is then heated to 200° C. at 6° C./min. by use of a Glas-Col hemispherical heating mantel connected to a programmable heat controller using a type J thermocouple. Once the temperature reached 200° C., the flask is kept at this temperature for 30 minutes. After the 30 minute hold, the flask is heated to 295° C. at a rate of approximately 5° C. per minute. The flask is maintained at a refluxing temperature of 295° C. for 30 min. before cooling down to room temperature under the Ar purge. Afterwards, all handling is performed open to the atmosphere. Purification of the nanoparticles is accomplished as follows: 5 mL of the dispersion taken from the flask is added to 20-25 mL of ethyl alcohol (“EtOH”) and the mixture is centrifuged 6000 rpm for 15 min. The supernatant is discarded and the precipitate is redispersed in 10 mL of hexane. The dark brown dispersion is stored under refrigeration at approximately 10° C. The FePt nanoparticles include an average size of 2 nm and have a spherical shape and narrow size distribution. The XRD patterns show that the FePt nanoparticles have a chemically disordered fcc structure. From the peak width of the XRD pattern, the average nanoparticle diameter of 1.6 nm is calculated using the Scherer formula.
In another embodiment, the magnetic nanoparticles are synthesized by surfactant-assisted ball milling, as disclosed in Chakka et al. “Magnetic Nanoparticles Produced by Surfactant-Assisted Ball Milling, J. Applied Physics, 99: 08E912 (2006), herein incorporated by reference. The starting powders have nanoparticle sizes from ˜10 to 45 μm (−325 mesh). Fe powders with 98% purity and Co powders with 99.5% purity may be used. Alloy powders of Sm—Co (1:5 and 2:17), NdFeB (2:14:1), and FeCo are prepared by arc melting followed by grinding. The milling process and handling of the starting powders and the milled particles are carried out in an oxygen-free inert environment. In one embodiment, argon gas is used inside a glove box; alternatively other inert gases may be used included N2 and the like. The starting powders are milled under a liquid or organic solvent, including ethanol or heptane. Heptane may include purity approximately 90-100%, alternatively 99.8%. The starting powders are also ball milled with a surfactant. Surfactants are characterized by having one long hydrocarbon chain per surfactant headgroup. In one embodiment, oleic acid and oleyl amine are used as surfactants during milling, where oleic acid may include a purity of 85-100%, alternatively 90% and oleyl amine may include a purity of 90-100%, alternatively greater than 98%. Other surfactants that may be used include, but are not limited, derivatives of oleic acid, erucic acid, linoleic acid, and the other long chain carboxylic acids surfactants. The surfactants used are absorbed by the fresh surface of particles crushed during the ball milling, leading to a surface modification for the ground particles. The amount of surfactant used is approximately 5-20% by weight of the starting powder, alternatively 7-15% or 10-12% by weight of the starting powder may be used. The mixtures were ball milled in a vibrating or rolling vial containing balls and the balls may include stainless steel, hardened steel, carbide or other ceramic balls. In one embodiment, high energy Spex 8000M mill with the milling vial and the balls made of 440 C hardened steel are used for milling the nanoparticles. The milling durations are from 1 to 50 hrs. The milling time and vibrating strength are adjusted to form the desired nanocomposite morphology. The ball to powder weight ratio may include 10:1 to about 2:1, alternatively 6:0.5 to about 7:3, or 5:1.
When the surfactant is used along with heptane during milling a colored liquid is obtained along with coarse particles, referred to as a slurry, which remain as sediment at the bottom of the milling vial after milling. The colored liquid contains a dispersion of nanoparticles smaller than 30 nm. As shown in
As shown in
In another embodiment, surfactant assisted ball milling includes starting powders of SmCO5 and Sm2Co17 with the starting powder sizes from approximately 1-45 μm, as disclosed in Wang et al. “Sm—Co hard magnetic nanoparticles prepared by surfactant-assisted ball milling” Nanotechnology 18: 465701 (2007), herein incorporated by reference. Organic solvent of heptane (˜99.8% purity) is used as the milling media and oleic acid (˜90%) and oleyl-amine (˜98%) are used as the surfactants during milling. The powders are ground in a milling vial with balls made of 440C hardened steel by using a Spex 8000M high energy ball milling machine. Milling process and handling of the starting materials and the milled products are carried out in an argon gas environment inside a glove box to protect the particles from oxidation. Typical milling duration used is 20 hrs. with balls of ¼ inch in diameter. The weight ratio of powder to ball is set as 1:10. The amount of surfactant used is approximately 8%-10% and the used solvent is about 55% of the weight of the starting powder, respectively. The ground slurry is then dispersed into heptane solvent by ultrasonic vibration and transferred to a 50 ml centrifugal tube for size selection. Fe, Co, FeCo, and Nd2Fe14B nanoparticles may also be used in the size selection process.
As shown in
As shown in
In another embodiment, the nanoparticles can be synthesized by a salt-matrix annealing technique, as disclosed in Rong et. al. “Size-dependent chemical and magnetic ordering in Ll0 FePt nanoparticles” Advanced Materials, 18: 2984-2988 (2006), herein incorporated by reference. The fcc-structured FePt nanoparticles with different sizes (from 2 to 15 nm) are synthesized using the airless chemical-solution method with adjusted synthetic parameters. The fcc particles are then mixed with ball-milled NaCl powder in hexane or another organic solvent with the assistance of surfactants. Dry mixtures of FePt particles and NaCl powders are obtained after the solvent is evaporated completely. The mixtures are then annealed in a forming gas (93% Ar+7% H2) at different temperatures for different times. After the annealing, the NaCl powder is washed away by deionized water and the FePt nanoparticles are recovered and dispersed in organic solvents, such as cyclohexane or ethanol, in the presence of surfactants. The elemental composition analyses, using inductively coupled plasma-optical emission spectroscopy (“ICP-OES”), show that there is negligible NaCl contamination in the salt-matrix-annealed FePt nanoparticles and the nanoparticle composition is Fe52Pt48. A transmission electron microscope is used to analyze the morphology and crystalline structures. X-ray diffraction (“XRD”) is used to determine the phase transition, the long-range ordering parameters, the grain size, and the nanoparticle size. The magnetic hysteresis loops are measured with a magnetic properties measurement system (“MPMS”) from specimens of a mixture of epoxy and the magnetic nanoparticles. Curie temperatures are measured by a physical properties measurement system (“PPMS”) with high-temperature and high-vacuum vibrating sample magnetometer. With this technique, nanoparticle aggregation during the phase transformation has been avoided so that the true size-dependent properties of the fct phase can be measured. FePt nanoparticles with different sizes are annealed in a salt matrix at 973 K for 4 hr. Nanoparticles with nominal diameters of 2, 4, 6, 8, and 15 nm, can be obtained, and TEM images are shown in
As shown in
Additionally, the magnetic nanoparticles may be coated with a shell of a non-magnetic, antiferromagnetic, or ferro/ferri-magnetic shell, which is otherwise known as a core/shell nanoparticle. A nonmagnetic coating is used routinely for magnetic core stabilization and surface functionalization for biomedical applications. An antiferromagnetic coating over a ferromagnetic core leads to exchange bias (a shift of the hysteresis loop along the field axis), and improvements in the thermal stability of the core. Compared with these two different types of core/shell systems, a bimagnetic core/shell one, where both core and shell are strongly magnetic (ferro- or ferri-magnetic) can be applied in electromagnetic and permanent magnetic applications. The intimate contact between the core and shell leads to effective exchange coupling and therefore cooperative magnetic switching, facilitating the fabrication of nanostructured magnetic materials with tunable properties. The bimagnetic core/shell also improves the compressibility in the warm compaction technique by controlling the soft phase shell thickness and composition. The ductility of the core/shell nanoparticles is increased compared with single-hard-phase nanoparticles. The increased ductility increases the warm compaction of core/shell nanoparticles. The core/shell nanoparticles can be also deformed to form texture during the warm compaction process.
In one example of coating the magnetic nanoparticles, monodisperse FePt nanoparticles are synthesized by thermal decomposition of Fe(CO)5 and polyol reduction of Pt(acaca)3, as disclosed in Chaubey et al., “Synthesis and Characterization of Bimagnetic Bricklike Nanoparticles” Chem. Mater. 20; 475-478, (2008), herein incorporated by reference. An iron oxide coating is achieved via mixing and heating the FePt nanoparticle seeds with Fe(acac)3/polyol, or Co(acac)2/Fe(acac)3/polyol precursors in phenyl ether in the presence of 1,2-hexadecanediol, oleic acid, and oleylamine. FePt/Fe3O4 nanoparticles are obtained by refluxing the FePt nanoparticle seeds with Fe(acac)3/polyol in the reaction mixture at 265° C. for 30 min. Bimagnetic FePt/Fe3O4 nanoparticles are isolated by centrifugation. The size of the soft phase could be controlled by varying the material ratio of FePt nanoparticle seeds to Fe(acac)3/polyol metal precursors. Reductive annealing can transform the bimagnetic nanoparticles into a hard magnetic nanocomposite with an enhanced energy product. In
FePt/FeCo nanoparticles are obtained with FePt nanoparticle seeds with Co(acac)2/Fe(acac)3/polyol precursors in phenyl ether in the presence of 1,2-hexadecanediol, oleic acid, and oleylamine, purging the mixture with argon for 30 min at room temperature and heating to 100° C. for 20 min. and then to 300° C. for 90 min., refluxed, and cooled to room temperature. The black product is precipitated by addition of 20 mL of ethanol and separated via centrifugation. The product is washed two or three times using a mixture of hexane (10 mL) and ethanol (40 mL) and separated via centrifugation. Finally, the product, FePt/FeCo nanoparticles is redispersed in hexane. The hexane dispersion of the bricklike nanoparticles is dropped onto a carbon-coated copper grid for use in transmission electron microscopy (“TEM”). The copper grid is placed in an alumina boat on a silica substrate. The boat is then placed in a heating furnace and purged with a gas mixture (93% Ar+7% H2) for 20 min. The samples are heated to the desired annealing temperatures under a continuous flow of the gas mixture. XRD analysis of the samples annealed at 500° C. show that the phase transformation of FePt from chemically disordered fcc to ordered Ll0 begun with the appearance of FePt Ll0 superlattice peaks. In
A typical procedure for obtaining FePt/CoFe2O4 bricklike nanoparticles having 8 nm FePt and 8 nm CoFe2O4 is the following: Co(acac)2 (0.05 mmol), Fe(acac)3 (0.1 mmol), 1,2-hexadecanediol (10 mmol), oleic acid (10 mmol), and oleylamine (10 mmol) are mixed in 20 mL of phenyl ether and magnetically stirred under an argon atmosphere, and 90 mg of 8 nm FePt seeds (dry powder) is added to the reaction mixture. After the mixture is purged with argon for 30 min at room temperature, it is heated to 100° C. for 20 min and then to 200° C. for 60 min., refluxed at 265° C. for 30 min., and finally cooled to room temperature. The black product is precipitated by addition of 20 mL of ethanol and separated via centrifugation. The product is washed two or three times using a mixture of hexane (10 mL) and ethanol (40 mL) and separated via centrifugation. Finally, the product, 8 nm FePt/8 nm CoFe2O4 bricklike nanoparticles, is redispersed in hexane. The structure of the nanoparticle assemblies is examined by transmission electron microscopy (“TEM”), electron diffraction, and x-ray diffraction (“XRD”). The magnetic properties are measured by a superconducting quantum interference device magnetometer.
Alternatively, the magnetic nanoparticles may also be synthesized by physical vapor deposition, chemical vapor deposition, reactive precipitation, sol-gel, microemulsions, sonochemical processing, supercritical chemical processing, magnetron sputtering and other methods known in the arts to give magnetic nanoparticles specific magnetic characteristics or microstructures. FePt nanoparticles are commonly fabricated using vacuum-deposition techniques. As deposited, the FePt has a chemically disordered fcc structure and is magnetically soft. Thermal annealing is needed to transform the fcc structure into the chemically ordered fct structure. However, the annealing also results in nanoparticle aggregation, leading to wide size distributions. To control the size and narrow the size distribution, FePt nanoparticles prepared from vacuum-deposition methods are often buried in a variety of insulator matrices, such as SiO, Al2O3, B2O3, or Si3N4. Alternatively, FePt particles can be made by gas-phase evaporation. Although the average size of these particles can be better controlled in the improved syntheses, it is still difficult to disperse them in various liquid media and to use them to form regular arrays. In contrast with all the physical deposition processes, solution-phase synthesis offers a unique way for producing monodisperse nanoparticles, and has been found to be particularly effective in synthesizing monodisperse FePt nanoparticles and nanoparticle super-lattices. Water-in-oil (“W/O”) microemulsions use fine microdroplets of the aqueous phase and are trapped within the assemblies of surfactant molecules dispersed in a continuous oil phase. The surfactant-stabilized microcavities provide confinement that limits nanoparticle nucleation, growth, and agglomeration. Sonochemical processing the acoustic cavitation, that is, the formation, growth, and implosive collapse of a bubble in an irradiated liquid, generates a transient localized hot spot, with an effective temperature of 5000K and a nanosecond lifetime. The cavitation is a quenching process, and hence the composition of the particles formed is identical to the composition of the vapor in the bubbles, without phase separation. High Power Impulse Magnetron Sputtering (“HIPIMS”), also known as High Impact Power Magnetron Sputtering and High Power Pulsed Magnetron Sputtering, (“HPPMS”)) is a method for physical vapor deposition of thin films which is based on magnetron sputter deposition. HIPIMS utilizes extremely high power densities of the order of kWcm-2 in short pulses (impulses) of tens of microseconds at low duty cycle (on/off time ratio) of <10%.EXAMPLES
The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compositions, systems, and/or methods claimed herein are made and evaluated, and are intended to be purely exemplary and are not intended to limit the scope of compositions, systems, and/or methods. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for.Example 1 FePt and Fe3O4 Bulk Nanocomposite
The FePt with face-centered cubic (“fcc”) structure and Fe3O4 nanoparticles are mixed at a mass ratio of 8:1 in a solution before centrifugation, as disclosed in Rong et al. “Bulk FePt-based nanocomposite magnets with enhanced exchange coupling”, J. Applied Physics, 101: 023908, (2007), herein incorporated by reference. The dried nanoparticles are heated before compacting under an Argon atmosphere at 350° C. for 1 hr. to remove surfactants. The powders are then compacted with a warm-compaction press under pressure of 0.5 to 6 GPa for a period of time and at a temperature. In one embodiment, the pressure is 2.5 or 3.8 GPa for 10 min. at temperatures ranging from room temperature (about 20° C.) to 600° C. The obtained bulk samples have dimensions φ6 mm×1.5 mm and φ3 mm×1.2 mm for the compaction pressures of 2.5 and 3.8 GPa, respectively. For comparison, 15 nm Ll0 FePt nanoparticles prepared by the salt-matrix annealing technique were compacted at 2.5 GPa pressure. The Archimedes method is employed for measurements of bulk sample density. The morphology and crystalline structure are characterized by scanning electron microscopy (“SEM”), transmission electron microscopy TEM, and x-ray diffraction XRD using Cu Kα. radiation. The composition of the compacted samples are checked by energy dispersive x-ray (“EDX”) analysis in SEM. Magnetic properties are measured with superconducting quantum interference device magnetometer with a maximum applied field of 70 kOe. For the ideal FePt/Fe composite, (BH)max=90 MGOe.
The bulk samples density ρp is dependent on the compaction temperature (“Tcp”) under different pressures. The density increases monotonously with compaction temperature for both fcc and Ll0 nanoparticle compacts. The samples prepared at pressure 3.8 GPa and Tcp of 600° C. has the highest density (13.8 g/cm3) which is about 95% of the full density value (14.5 g/cm3 for the FePt/Fe3Pt composite with 15% volume fraction of Fe3Pt phase). Such a high density is a result of a significant plastic deformation of the nanoparticles at the applied high pressure. A linear increase in the density can be observed for the Ll0 particles in the whole studied temperature range and for the fcc particles in the temperature range from 20 to about 400° C. This may be explained by the fact that the yield strength of metallic FePt materials decreases linearly with temperature in the region between 20 and 800° C. and an effective lubrication mechanism can occur in the heated powders. However, this linear increase in density did not lead to full densification, even when extrapolating the curve to a high temperature.
As shown in
SEM analysis is performed on the fracture surfaces of the compacts to characterize morphological changes in the compacted samples. Typical SEM images of the bulk samples compacted at 20, 400, and 600° C. are shown in
The rapidly increased density at the compaction temperature higher than 400° C. may be related to the phase transition of FePt component from fcc structure to the Ll0 structure. XRD measurement of the 20, 400, and 600° C.-compacted samples and the patterns are performed to study the phase transition, as shown in
The degree of phase transition from the disordered fcc to the ordered Ll0 structure is evaluated in a quantitative way, with the chemical ordering parameter S calculated by S≈0.85 [I001/I002]1/2 for the compacts and starting powders, where I001 and I002 are the integrated intensity of (001) and (002) XRD peaks of the Ll0-FePt phase, respectively. As shown in
The phase transition is also confirmed by the dependence of magnetic properties on Tcp As shown in
X-ray diffraction line-broadening analysis is performed on the bulks to quantitatively determine the effect of warm compaction on the microstructure. As shown in
As shown in
As shown in
Exchange Coupling and Magnetic Properties
Controlling the grain size of the compacts realizes intergrain magnetic exchange coupling and achieves high energy products. The δm=md(H)−(1−2mr(H)) measurements (Henkel plots) is performed to study the magnetic interactions in the warm compaction-produced nanocomposite magnets. Here md is demagnetization remanence and mr is isothermal magnetization remanence. Both of these values are normalized by the saturation remanence. Nonzero δm is caused by magnetic interactions between particles or grains. The positive δm is interpreted as a sign for magnetic exchange coupling and the negative δm is a sign of magnetic dipolar interaction. As shown in
The magnetic properties can be further improved by a post-annealing under forming gas (93% Ar+7% H2) for 1 hr. The effect of annealing temperature (“Tα”) on Ms, Hc, and (BH)max of the 20, 400, and 600° C. compacts, is shown in
Alternatively, the SmCo/Fe bulk magnets are processed by ball milling of the SmCo and Fe powders into nanocomposites and warm compacting the nanocomposite powder particles to form 6-9 mm samples at 3.5 GPa at <600° C., where the grain size is in low nanoscale region.
The grain size is in low nanoscale region.
The SmCO5/Fe bulk magnet performance showed the first exchange-coupled nanocomposite isotropic SmCo/Fe magnets.
Nanoparticle deformation mechanism and interface atom diffusion may optimize warm compacting parameters. Utilization of parallel computing programs and Atomistic Computer Simulations may detect increased deformation at and through grain boundaries to increase the bulk nanocomposite produced by the warm compaction method, as disclosed in Swygenhoven et al., “Deformation in Nanocrystalline Metals”; Mats. Today; 9; 5 2006, 24-31, herein incorporated by reference. Increased deformation at and through the grain boundaries will increase the density and the magnetization of the compacts.Example 4 Naval Applications
The bulk nanocomposite magnets may be used in axial field permanent magnet motor/centrifugal pump to improve reliability in naval applications. Radial field permanent magnet motors have been demonstrated for quiet undersea vehicle propulsion. The bulk nanocomposite magnets may also be used for integrated motor/propulsors in naval machines.Example 5 Hybrid Cars
Warm compacted bulk nanocomposites may provide energy enhancement for hybrid cars for increased energy efficiency.Example 6 Wind Energy
Wind energy turbines use permanent magnet generates in the generator's gear box. The bulk nanocomposites may be used in the generator gear box for wind energy turbines.
It will be apparent to those skilled in the art that various modifications and variations can be made in the embodiments disclosed herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the embodiments disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
1. A composition of magnetic nanoparticles comprising:
- a. a plurality of magnetic nanoparticles produced by surfactant-assisted ball milling, wherein the magnetic nanoparticles have an average size below about 100 nm; and
- b. the magnetic nanoparticles comprise at least one of FeO, Fe2O3, Fe3O4, Co, Fe, Ni, CoFe, NiFe, CoO, NiO and ferrites including MFe2O3 where M comprises one of the transition metallic elements including Co and Ni; and FePt, CoPt, SmCo-based alloys, including SmCO5, Sm2CO17, Sm2CO7, and SmCO7, and rare earth-FeB-based alloys, including R2Fe14B, where R comprises one of Nd and Pr.
2. The magnetic nanoparticles of claim 1, wherein the Sm—Co based alloys include an average size of 23 nm, a coercivity of equal or larger than 3.1 kOe, and an elongated rod-shape.
3. The magnetic nanoparticles of claim 1, wherein the Fe—Co based alloys include an average size of at least about 1.7 to 4.0 nm and an ultrafine spherical shape.
4. The magnetic nanoparticles of claim 1, wherein the Sm—Co, NdFeB, and Co magnetic nanoparticles include an elongated rod-like shape.
5. A bulk magnetic nanocomposite comprising:
- a. a soft phase material with particle size from at least about 2 nanometers to 100 micrometers comprising at least one of FeO, Fe2O3, Fe3O4, Co, Fe, Ni, CoFe, NiFe, CoO, NiO and ferrites including MFe2O3 where M comprises one of Co and Ni;
- b. a hard phase material with particle size from 2 nanometers to 100 micrometers comprises at least one of FePt, CoPt, SmCo-based alloys, including SmCO5, Sm2CO7, Sm2CO17, and SmCO7, and rare earth-FeB-based alloys, including R2Fe14B, where R comprises one of Nd and Pr;
- c. wherein the hard phase material and the soft phase material is warm compacted to form a bulk nanocomposite.
6. The bulk magnetic nanocomposite of claim 5, wherein the soft phase material and the hard phase material comprise interphase exchange coupling and the hard phase material is aligned.
7. The bulk magnetic nanocomposite of claim 6, wherein the soft phase material and the hard phase material includes a grain size in the nanoscale.
8. The bulk magnetic nanocomposite of claim 7, wherein the density of the nanocomposite is between at least about 50% to 100% of the theoretical density.
9. The bulk magnetic nanocomposite of claim 8, wherein the hard phase material and the soft phase material comprise magnetic nanoparticles.
10. A process of forming a plurality of magnetic nanoparticles comprising:
- a. providing a powder with particles of first size in an inert environment;
- b. dissolving the powder in a first solvent with a surfactant;
- c. ball milling the powder into a plurality of nanoparticles having a second size;
- d. dispersing the nanoparticles into a second solvent; and
- e. separating the nanoparticles by a size selection process.
11. The process of claim 10, wherein the powder is selected from one of FeO, Fe2O3, Fe3O4, Co, Fe, Ni, CoFe, NiFe, CoO, NiO and ferrites including MFe2O3 where M comprises one of Co and Ni, FePt, CoPt, SmCo-based alloys, including SmCO5, Sm2CO17, Sm2CO7, and SmCO7, and rare earth-FeB-based alloys, including R2Fe14B, where R comprises one of Nd and Pr.
12. The process of claim 11, wherein the powder is a SmCo-based alloy and the ball milling step includes a weight ratio of the powder to the ball mill comprises about 1:10.
13. The process of claim 10, wherein the separating step comprises a spinning step of about 1600 g of relative centrifugal force for a period of time and separating a first supernatant from a first slurry to obtain a plurality of nanoparticles with an average size distribution of about 4 to about 10 nm.
14. The process of claim 13, further comprising
- a. washing the first slurry with a solvent;
- b. dispersing the first slurry in a surfactant-coated centrifugal tube by ultrasonic vibration;
- c. settling down the dispersed solution for about 2 to about 5 hours;
- d. spinning the settled down solution at about 45 g of relative centrifugal force; and
- e. separating a second supernatant from a second slurry to obtain a plurality of nanoparticles with an average size distribution of about 10 to about 15 nm.
15. The process of claim 13, further comprising:
- a. washing the first slurry with a solvent;
- b. dispersing the first slurry in a surfactant-coated centrifugal tube by ultrasonic vibration;
- c. settling down the dispersed solution for about 20 to about 30 minutes;
- d. spinning the settled down solution at about 45 g relative centrifugal force; and
- e. separating a second supernatant from a second slurry to obtain a plurality of nanoparticles with an average size of about 23 nm.
16. A process of forming a bulk nanocomposite magnet, comprising:
- a. mixing at least one hard phase magnetic material and at least one soft phase magnetic material in a solution with original particle size from at least about 2 nanometers to 100 micrometers;
- b. spinning the solution and drying the solution;
- c. heating the dried hard and soft phase material under an inert atmosphere at a first temperature for a first period of time to form a second powder; and
- d. compacting the second powder under a first pressure at a second temperature for a second period of time to produce a bulk nanocomposite magnet having a bulk dimension.
17. The process of claim 16, where the soft phase material comprises at least one magnetic nanoparticle of FeO, Fe2O3, Fe3O4, Co, Fe, Ni, CoFe, NiFe, CoO, NiO and ferrites including MFe2O3 where M comprises one of Co and Ni; and the hard phase material comprises at least one magnetic nanoparticle of FePt, CoPt, SmCo-based alloys, including SmCO5, Sm2CO17, Sm2CO7, and SmCO7, and rare earth-FeB-based alloys, including R2Fe14B, where R comprises one of Nd and Pr.
18. The process of claim 17, wherein the hard phase material comprises the magnetic nanoparticle FePt with fcc structure and the soft phase material comprises the magnetic nanoparticle Fe3O4, wherein the compacting step compacts the magnetic nanoparticle FePt from the fcc structure to the Ll0 structure.
19. The process of claim 16, wherein the mixing step further comprises ball milling the hard and soft phase magnetic nanoparticles under a gas or a liquid in a vibrating vial, wherein the milling time and vibrating strength are adjusted to form a nanocomposite morphology.
20. The process of claim 17, wherein the first pressure comprises at least about 1.0 GPa, the second period of time comprises at least 10 minutes, and the second temperature includes a range of about 20° C. to about 800° C.
21. The process of claim 20, further comprising annealing the bulk nanocomposite magnet under a forming gas for a third period of time and at a third temperature of about 20° C. to about 800° C.
International Classification: B22F 3/12 (20060101); B22F 1/00 (20060101); B22F 9/16 (20060101); B29B 9/00 (20060101);