Propellants and high energy materials compositions containing nano-scale oxidizer and other components

Abstract

Propellants and high energy materials compositions containing nano-sized oxidizer and other components. The propellant composition simulates a monopropellant formed by nano-sized propellant ingredients in the form of nano-scale reactors. When forming such monopropellant-like compositions, a protective coating is provided around the reactive ingredient. Coating the metal particles prevents formation of an oxidation layer.

Description

PRIORITY CLAIM

The present invention claims benefit of the U.S. provisional application No. 60/593,395 filed on Jan. 11, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to the field of propellants and energetic materials compositions and more particularly to propellant compositions containing nano-sized (less than 500 nm or 0.5 micron diameter) oxidizer and fuel components and partially nano and micron sized mixtures of various components providing nano-scale or micro-scale reactors. The compositions containing nano-scale materials are protected from mutual interaction by way of coating or encapsulation.

2. Brief Description of the Prior Art

Propellant compositions usually contain an oxidizer, a polymeric fuel binder, a gelling agent, and various other additives depending upon the type of propellants such as solid, liquid, or a gel. A majority of solid composite propellants use metals in order to increase the burn rate and the specific impulse of propellant formulations. Propellant compositions containing metals such as aluminum, boron, magnesium, and titanium are known. The majority of propellant compositions used for rocket and missile propulsion use aluminum as a fuel because of the low cost of aluminum. In addition, Aluminum ignites and burns relatively more easily than other ingredients.

Recent research on propellants has demonstrated the incorporation of nano-particles of aluminum to increase the burn rate in current propellants. Nano-sized (50 to 200 nanometer diameter) aluminum particles have been tested in propellant compositions and their initial laboratory results indicate burn rate increase of such propellants. However, the great challenge in the prior art area is the high oxidation rate and stability of nano-sized aluminum powder in oxidizer compositions. The extent of oxidation can go up to 40% wt for 50-100 nm aluminum. A similar trend in the formation of an oxidation layer is seen for boron containing propellants as disclosed in U.S. Pat. Nos. 3,354,172; 4,141,768; 5,074,938; and 5,837,930. Boron has a low molecular weight and a high energy of combustion, making it an attractive fuel for propellant formulations (U.S. Pat. No. 6,652,682). However, the oxide layer inhibits combustion.

The prior art clearly shows the absence of research and formulations of high energy solids, explosives and propellants containing nano-sized (or below 10 micron) oxidizer particles. U.S. Pat. No. 6,576,072 issued to Chan et al. on Jun. 10, 2003 discusses propellant compositions containing poly-dispersed particle sizes. They used 25-32% wt ammonium perchlorate (AP) with extremely small particles of 10-15 micron and 18-24% wt of larger particles and other co-oxidizers such as ammonium nitrate. The main objective of their work was to achieve propellants which are insensitive to over-pressures in the combustion chamber. Chan et al. claim oxidizers of less than 200 micron size and poly-disperse compositions, the propellants show good performance in relation to chamber pressure response and combustion efficiency.

Based upon the above, it is highly desirable to provide propellant and explosive compositions containing nano-sized particles of oxidizers, polymers, and metallic fuels, which are mutually protected, and are compatible in their compositions. The extremely small particles are less sensitive to chamber over pressure and help accelerate burn rate and hence specific impulse of these propellant compositions.

SUMMARY OF THE INVENTION

Accordingly, it is an objective of this invention to provide a propellant composition comprising nano-sized oxidizers, carbonaceous fuels, metallic fuels, and polymers that are mutually stabilized by selective nano-coating and co-deposition of various ingredients.

It is another objective of this invention to use a selected morphology of nano-sized oxidizer particles synthesized (generated) by low temperature drying. Some useful particle shapes include, but are not restricted to, doughnut shapes, smaller circles, and tubes. These shapes will be effectively filled with desired components to form a nano-composite.

It is another objective of this invention to prepare nearly monopropellant compositions by way of mutual coating and co-deposition of ingredients at the nano-sized level, particularly, 0-200 nm. The resulting nano-scale reactor will contain oxidizing and reducing components approximating a single monopropellant molecule.

It is another objective of this invention to provide encapsulation methods to stabilize high-energy solids in order to reduce the sensitivity to thermal as well as mechanical shocks.

It is another objective to achieve an efficient ignition of propellant composition by way of nano-scale reactors with extremely small particles and hence greater surface area.

It is another objective to achieve pressure insensitive compositions by way of nano-sized and poly-disperse particles by providing for product composition retaining the maximum packing density.

It is another objective to use a highly porous oxidizer in the form of a “nano-porous” material so that fuel nano-scale particles can be incorporated at the nano-level so that the resultant composition will be more like a nano-sized monopropellant.

It is another objective to achieve a relatively high burn rate using a nano-sized oxidizer without using exotic burn rate accelerators such as ferric oxide, copper chromate etc.

It is another objective to use mixtures of oxidizers such AP, AN, HMX and other oxidizers by co-dissolving and drying them to sub-micron particles and thus help to maximize specific impulse by enhanced energetics as well as enhance combustion behavior.

It is the final objective to achieve peak specific impulse from the propellant and other high energy solid systems by increasing the combustion efficiency of particles by way of providing the nano-reactor compositions of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an embodiment of the invention for nano-scale composite particle formulation with nano-particle reactors as monopropellants.

FIG. 2 is a schematic view of an embodiment of the invention for nano-scale reactor formulation with a desired oxidizer, fuel and metal composition.

FIG. 3 is a schematic view and model of an embodiment of the invention for formation of nano-scale porous oxidizer particles absorption of fuel composition.

DETAILED DESCRIPTION OF INVENTION

The fundamental theme of using nano-scale sized particles in propellants is to transition from diffusion controlled reactions derived from large particle formulations to a kinetically controlled nano-reactor concept. In the nano-scale kinetically controlled reactor formulation, ideally, the particles at the nano-level behave as though molecularly mixed. Thus, it is desirable for the particles to undergo a kinetically controlled premixed reaction. The limits of combustion efficiency in chemical propulsion are being increased by moving from diffusion controlled reactions to premixed molecular level reactions. The nano-reactors provided by the invention behave like monopropellants in which reactive components consisting of oxidizing and reducing valances are in the same molecule. This monopropellant like configuration is the most desired propellant composition for achieving the peak specific impulse by way improving the combustion behavior. However, nano-reactors has provided for by the invention have not been achieved previously because composite propellants generally are heterogeneous at the particle level.

Because of the behavior of extremely fine particles, such as nanometer sized particles, the combustion process of the present reactor compositions is largely kinetically controlled rather than diffusion controlled as in standard sized powders. The nano-sized oxidizers are coated with polymeric or fuel binders. The coating prevents the compositions from prematurely interacting with each other. Thus, the coated oxidizers are less sensitive to thermal and mechanical shock and can reduce pre-oxidation of metal particles in contact with the oxidizers. Further, the product composition disclosed is pressure insensitive, as achieved by way of nano-scale sized and poly-disperse particles allowing the composition to attain the maximum packing density. Thus, using nano-scale oxidizing particles to form the nano-scale composition provides the highest mechanical strength and excessive chamber pressure tolerance. The composition can be further pressed to impart additional mechanical strength.

Morphology of particles obtained by using suitable processes such as a low temperature drying process create nano-scale oxidizer compositions or particles. With respect to low-temperature drying in particular, a low velocity precursor mist is formed by atomizing a particle precursor solution by an ambient-pressure and ambient-temperature atomizer. The precursor mist is mixed with a drying gas into a reactant stream that is introduced into a dryer through a swirl generating inlet. The reactant stream is moved through the dryer in a helical flow. The temperature and duration of the drying process can be readily controlled to create the desire quality particles. The drying method also provides process technology for producing nano-porous oxidizer materials by addition of agents causing such pores.

The final particle size obtained by this method can be varied. The preferred range of particle size for nano-scale propellants and like high-energy material compositions is 50-200 nm. The resulting size of the propellant compositions containing oxidizer, fuel, metallic fuels and other major ingredients may be controlled using the processes discussed such that the propellant compositions have nanometer or sub-micron sized particles constituting the major proportions of the particles up to 100%.

By way of an example, oxidizer particles may be obtained with doughnut and small circular shapes or tubes. These and other particle morphologies are used for incorporating the main ingredients of the propellants such as oxidizers, carbonaceous fuels and metallic fuels like Al, Mg, Be and other high energy metals. Suitable oxidizers may, but is not restricted to, ethyl ammonium nitrate (EAN), triethyl ammonium nitrate (TEAN), yclotetramethylenetetranitramine (HMX), trinitrotoluene (TNT), hydroxyl ammonium perchlorate (HAP), hydroxyl ammonium nitrate (HAN), ammonium perchlorate, ammonium nitrate, ammonium dinitramide (ADN), hydrazinium mononitrate, or a combination thereof. The propellant composition contains 1-80% oxidizing agent, and remainder is carbonaceous fuel, metallic fuels, gelling agents, and curing agents necessary to formulate the propellant grain. The proportion of ingredients can be varied at will to maximize performance and mechanical properties.

The present invention relates to both propellant and explosive compositions. Polymer coatings will comprise CTPB (carboxyl terminated poly butadiene), HTPB (hydroxyl terminated poly butadiene) and other carbonaceous materials. These polymer coatings can be co-dissolved or coated onto the oxidizer or metal particle, or both. Propellant and explosive fuel particles may include nano-scale particles of aluminum or boron, which may be synthesized, preferably using decomposition of organo-metallic compounds. These propellant or explosive fuel particles are coated before mixing with oxidizers.

There are several process arrangements for forming a nano-scale propellant composition in accordance with the invention. These processes will provide compositions having the desired ingredients with fine particles of less than one micron diameter or less than 10 micron diameter. These fine particles are referred to herein generally as being on a nano-scale with regard to size.

In a first embodiment a nano-scale composite particle referred to herein as a nano-reactor is formed to provide the propellant composition. A precursor solution is prepared with a desired concentration of components. For example, the solution may contain ammonium perchlorate (AP), polymer and nano-scale AI particles forming a precursor or nano-scale aluminum. The solution is atomized and dried by the low temperature drying methodology discussed. In one embodiment of the propellant composition, liquid oxidizer droplets can be encapsulated by a suitable coating agent prior to drying. The dried particles now comprise a composite material of all ingredients needed to form a nano-scale reactor material. The schematic of this procedure is shown in FIG. 1. The formulation is particularly useful for explosives or propellants not containing reactive metal additives.

In a second embodiment a nano-scale porous material is formed to provide the propellant composition. Where the ingredients are highly porous structures made up of nano primary particles, the porous structure allows preferential coating of ingredients. The oxidizer material is dried to form nano-sized porous materials using the low temperature drying methods discussed. After formation the nano-scale porous oxidizer is filled with other ingredients by absorption or filling in of the nano-porous structure of the porous oxidizer material.

Propellant formation may be varied by selective coating and co-dissolving with precursors, providing for nano-scale coating of the particles. For example, depending on reactivity of oxidizer, fuel and metallic fuel reactivity and how each individually stabilizes in the particle, selective processing is necessary. In other words, the components of the propellant ingredient may have to be protected from each other.

As shown in FIG. 2, the coating process may operate in a series of steps. The process loop can achieve desired particle compositions by way of repeated coatings in the series. For example, first AP (or any other oxidizer) solution is atomized and dried. The dried AP nanoparticle is then coated with fuel spray. The oxidizers are nano-sized or less than 10 micron and are coated with the fuels. The mixture is dried to get AP in combination with the fuel coated particle, AP+Fuel. The product then enters the last step in the loop where the particles are coated with nano-scale AI. Then, the mixture is dried to get an AP+Fuel+AI particle containing an intermediated composition. Now this product enters the loop again for a fuel coating to protect the AI from contacting the AP during the second pass. After the second pass, the product moves out of the loop as a nano-scale propellant or also referred to herein as a nano-scale reactor.

Other embodiments are possible which are within the ability of those who are skilled in the art. Aluminum is provided as an example above. It is appreciated that other metal additives such as boron, beryllium, magnesium and the rest of the high energy metals are equally applicable.

It is further appreciated that another embodiment formulates the propellant containing nano-scale particles. This uses nano-scale oxidizer particles and coated nano-scale aluminum particles in polymeric fuels. The formulation is similar to advanced propellants, but containing nano-scale sized oxidizers. The new formulation containing nano-scale particles will burn faster and more efficiently because of nearly premixed combustion process.

Another preferred embodiment of the invention is a propellant composition that simulates a monopropellant. The simulated monopropellant is formed by nano-scale sized propellant ingredients in the form of nano-scale reactors. When forming such monopropellant-like compositions, a protective coating is provided around the reactive ingredient. Coating is necessary for the metal particles in order to prevent formation of an oxidation layer. It is also necessary to avoid premature ignition of the monopropellant nano-scale reactors. Examples of such protective coatings include polymeric substances or plastic coatings.

The nano-scale or sub-micron sized metallic fuel component may be coated with a carbonaceous fuel. As a result of coating the fuel component therewith, the carbonaceous fuel is in contact with oxidizer to prevent the oxidizer layer formation and pre-mature ignition where selected ingredients. The carbonaceous fuel provides beneficial coating were the components are co-dissolved in a solvent or formed into micro-emulsions and dried to form extremely small particles. The oxidizer particle morphology in this scenario may include, but is not restricted to doughnuts, smaller circles and tubes, so that the other ingredients can be combined to form nano-scale reactors.

The present invention also comprises explosive compositions or high-energy compositions where the compositions have to be stabilized by nano-coating of ingredients in order to achieve insensitive behavior. And/or, explosive compositions where specific performance behavior has to be “tailored” by controlling the chemical and physical processes. And/or, explosive compositions where the material must be protected from moisture and hygroscopic nature. And/or, light sensitive high-energy compositions that must be protected from light sources. The composition may also include explosive materials without containing a polymeric binder.

In view of the invention, some of the oxidizers that are very reactive but do not contain chlorine may find increased use in the future including oxidizers that are hygroscopic and oxidizers including ADN, HNF and CL-20. Use of a mixture of oxidizers such AP, AN, HMX and other oxidizers may be accomplished by co-dissolving and drying them to sub-micron particles. This will allow maximizing specific impulse by energetics, as well as by improving combustion behavior. The molecular formula and thermochemical properties are listed below.

ADN

• • Heat of formation=−148 kJ/mol
  • Density=1.818 g cm-3
  • Melting pt _iÖ92° C.
  • Auto Ignition T.=160° C.

% CO+O2=25.8

• • NH4N NO2 NO2

HNF

• • Heat of formation=−72 kJ/mol
  • Density=1.870-1.910 g cm-3
  • Melting pt _iÖ115° C.
  • DSC onset 121-129° C.

% CO+O2=21.8

• • O2N C NO2 NO2 N2O5

CL-20

• • Heat of formation=372 kJ/mol
  • Density=2.04 g cm-3
  • Melting pt>195° C.

% CO+O2=10.9

• • N N N N N N NO2 NO2 NO2 NO2 NO2 NO2

These oxidizers are good candidates for nano-scale reactor formulations because most of them melt at low temperature, such as less than 100° C. and have low ignition temperature. The presence of stabilizing coating makes this possible. Thus, by making nano-scale composites in accordance with the invention, these new formulations can be stabilized.

Although the illustrative embodiments have been described herein with reference to the accompanying drawings, it is to be understood that the present invention is not limited to those precise embodiments, and that various other changes and modifications may be affected therein by one of ordinary skill in the related art without departing from the scope or spirit of the invention. All such changes and modifications are intended to be included within the scope of the invention as defined by the appended claims

Claims

1. Propellants and high energy materials compositions containing nano-sized oxidizer and other components.