US Government As Represented by the Secretary of the Army

Darren M Thompson

William M Chew

Barry D Allan

Leo K Asaoka

Larry C Warren

Douglas L May

Tactical missile propellant formulations are inherently sensitive to impact and friction stimuli. The impact and friction insensitivity of some tactical propellant formulations is improved significantly when internal conductive polymers PERCOL&reg;292, (copolymer of a quaternary acrylate salt and acrylamide, Allied Colloids, Inc.) and VERSICON&reg;, (Polyaniline)(Emeraldine salt), green/black powder, Monsanto Company) are added to the formulation. These two conductive polymers were evaluated in a high performance propellant formulation containing the same ingredients now being used in fielded tactical missiles. The impact and friction insensitivity of propellants containing these conductive polymers was improved thirty and sixty six percent, respectively.

Conductive polymers to improve propellant insensitivity-impact and friction-properties

The subjects of this patent are three amine azide monopropellants, dimethylaminoethylazide (DMAZ), pyrollidinylethylazide (PYAZ) and diethylaminoethylazide (DEAZ). Amine azides decompose on an iridium catalyst at 400&deg; F. and have very low freezing points (<&minus;65&deg; F.). Dimethylaminoethylazide (DMAZ) has been tested and is a suitable replacement for hydrazine in monopropellant thruster applications. An amine azide can be used as a non-carcinogenic alternative for any monopropellant system using hydrazine. An amine azide could be used to replace hydrazine in thrust vector control or reactive control applications for space based applications. An amine azide could be used to replace hydrazine in divert attitude control systems in interceptor missile systems. In a gel fuel formulation the tertiary amine azide gel can have 0.5%-10% gellant. The gellant can be silicon dioxide, clay, carbon or any polymeric gellant. The amine azide gel can also include additives that could improve the specific impulse and density impulse. These solid additives include but would not be limited to amine-nitrate salts, quaternary ammonium salts or other high-density additives. The formulation can vary over the following ranges 1%-90% solid additive, 100%-10% tertiary amine azide and 0.5%-10% gellant.

Amine azides used as monopropellants

A liquid gas generator system supplies gas pressure only when it is needed. Hydrazine and hydrazine blends have been considered for liquid gas generators because of their ability to decompose at ambient conditions on an iridium catalyst to form warm (1000&deg; F. to 1500&deg; F.) gases. Hydrazine is undesirable because of its toxicity and high melting point (34&deg; F.). The tertiary amine azides, which are defined hereinabove and below, are non-carcinogenic alternatives to hydrazine in liquid or gel gas generator systems. These tertiary amines azides are non-carcinogenic alternatives for use with a thermal reactor bed where exothermic reaction releases enough heat to sustain decomposition for furnishing gases for gas generator systems employed. A tertiary amine typically has three hydrocarbons moieties attached to the nitrogen atom. The tertiary amine azides of this invention can have no more than seven carbon atoms in the molecules. Further, these tertiary amine azides can contain no more than two azide moieties that are attached at the opposite end of the hydrocarbon portions from the amine nitrogen atom. A special case that still meet these requirements is pyrollidine moiety (five atom cyclic structure wherein each end of a linear four carbon atom structure is attached to a common nitrogen atom), and the common nitrogen atom has as attached ethyl azide moiety. A fuel gel propellant fuel that would be a suitable replacement for MMH must be less toxic and have a competitive density impulse for the same engine operating conditions. Three compounds meeting the specified requirements have been synthesized and their physical and chemical properties are evaluated herein as shown in Table 1. The chemical names for these compounds are dimethylaminoethylazide (DMAZ), pyrollidinylethylazide (PYAZ), and bis(ethyazide)methylamine (BAZ). DMAZ has a density of 0.933 and a heat of formation of 580 (cal/g) as compared with MMH having a density of 0.88 and heat of formation of 276 (cal/g).

Tertiary amine azides in liquid or gel fuels in gas generator systems

A high density inhibited red fuming nitric acid oxidizer gel is disclosed ich results in an improvement from 0.5% to about 1.0.% in the impulse over a baseline formulation containing 14% nitrogen tetroxide. An improvement from about 3.0% to about 6.0% is achieved in the density impulse baseline formulation. The higher density inhibited red fuming nitric acid is derived by adding from about 15 percent by weight to about 45 percent by weight percent of nitrogen tetroxide to nitric acid in an amount from about 80 percent by weight to about 40 percent by weight. The other ingredient of the oxidizer gel comprise a gellant of about 0-10 percent by weight, water from about 0-4 percent by weight, and an inhibitor agent of about 0-1 percent by weight. IRFNA is inhibited with phosphoric acid, iodine compounds, or hydrogen fluoride which is present in the oxidizer gel as an additive. The higher density IRFNA oxidizer gel or liquid can be used in airbreathing propulsion systems; a bipropellant formulation is used to provide variable thrust. The oxidizer can also be used with air turbo rocket propulsion systems to augment air combustion with fuel gases. It can be used in a liquid or gel/solid system wherein the oxidizer is sprayed in contact with a solid propellant.

Higher density inhibited red fuming nitric acid (IRFNA) oxidizer gel

Inhibited Red Fuming Nitric Acid (IRFNA) type IIIB and monomethyl hydrazine (MMH) ignite when contacted with each other because of a hypergolic chemical reaction and are the preferred oxidizer and fuel for bipropellant rocket propulsion systems. These propellants can deliver a specific impulse of 284 lbf sec/Ibm and density impulse of 13.36 lbf sec/cubic inch when the engine operating pressure is 2000 psi. Special precautions must be used when handling because of its toxic properties. A fuel gel propellant fuel that would be a suitable replacement for MMH must be less toxic and have a competitive density impulse for the same engine operating conditions. Three compounds meeting the specified requirements have been synthesized and their physical and ballistic properties are evaluated herein as shown in Table 1. The chemical names for these compounds are dimethylaminoethylazide (DMAZ), pyrollidinylethylazide (PYAZ), and bis (ethyl azide)methylamine (BAZ). DMAZ under the same operating conditions can deliver a specific impulse of 287 lbf sec/Ibm and a density impulse of 13.8 lbf sec/cubic inch.

Tertiary amine azides in hypergolic liquid or gel fuels propellant

Tungsten is added to fuel gels to increase the density specific impulse. l gels contain monomethylhydrazine or other hypergolic liquids well known in the art. The quantity of tungsten employed can vary from 10%-98% weight percent depending on the specific application. The important parameters to consider during formulation are particle size, concentration, combustion efficiency, physical properties, and plume signature. Tungsten particle sizes ranging from 10 microns to 0.5 micron were compared with carbon of 0.24 when burned in air. It is shown that tungsten burns as well as or better than carbon; however, the increased density specific impulse achieved with tungsten as compared with carbon verifies that tungsten as a high energy additive to hypergolic fuel gels is superior. The burning temperature with small particle size tungsten is controlled to yield a plume with minimum signature since all of the tungsten exist in the gaseous state in the exhaust gases thereby yielding an exhaust plume which is transparent as attractive for tactical missiles to avoid detection.

Tungsten as a hypergolic fuel gel additive

A hypergolic fuel formulation which is consistently hypergolic with inhibd red fuming nitric acid is comprised of diethylethanolamine from about 44-72 weight percent, triethylamine from about 11-18 weight percent, and carbon from about 45-10 weight percent The formulation can be gelled with: silica, clays, carbons, or swellable polymers. The gellants can be combined with chemical agents that stabilize the gel under the standard 30 minute, 500 g centrifuge stability test. A preferred combination comprising diethylethanolamine in an amount of about 44 weight percent, triethylamine in an amount of about 11 weight percent, and carbon in an amount of about 45 weight percent when tested at an oxidizer/fuel ratio of about 4.25 reveals theoretical performance values of specific impulse (ISP) of about 250 at a chamber pressure of 1000 Psi and a density specific impulse (D* ISP) of about 350. The performance values of ISP and D*ISP when the specified combination is tested at the same oxidizer/fuel ratio and at a chamber pressure of 2000 Psi reveals are about 265 and about 372, respectively.

Hypergolic fuel formulation: diethylethanolamine, triethylamine, and

A gas generator propellant formulation suitable for use in an air turbo ret (ATR) which employs an air breathing system that uses fuel gases produced by a gas generator propellant to operate the engine's turbine is provided which can also be used with other airbreathing propulsion systems that require a high gravimetric heating value (GHV). The basic fuel gas generator propellant formulation comprises in weight percent a tetraalkylammonium borohydride 50-100; lithium nitrate 0-50; and optional additives of hydroxy proply cellulose 0-20 and silica or silicon 0-20. The basic fuel gas propellant formulation can also employ an encapsulated tetraalkylammonium borohydride which employs an encapsulation polymer selected from the group consisting of polyethylene, polypropylene, and ethyl cellulose. When employing an encapsulated tetraalkylammonium borohydride a binder is employed selected from the group consisting of polybutadiene and polyether cured with 0.50% selected from hexamethylene diisocyanate and isophorene diisocyanate. The encapsulated fuel gas generator propellant formulation comprises an encapsulated tetraalkylammonium borohydride 50%; binder 0-45%; and lithium nitrate 5%. Lithium nitrate in the fuel gas generator propellant formulation enables the composition to be ignited with a hot wire. The tetraalkylammonium borohydride is selected from the group of tetraalkylammonium borohydrides consisting of tetramethylammonium borohydride, tetraethylammonium borohydride tetrapropylammonium borohydride, and tetrabutylammonium borohydride.

Fuel gas generator for airbreathing propulsion systems

Elemental silicon is a solid high energy material which provides an advane when added to gel, hybrid, and ducted rocket fuels by increasing both specific impulse, lsp, and density specific impulse, .rho.*lsp. The quantity added depends on the specific applications for which the formulation will be used. The usual concentration ranges from about 0.5% to about 70% by weight. The important parameters to consider during formulation are particle size, concentration, combustion efficiency, physical properties, and plume signature. Comparisons for 50% solid fuel loading in a gel bipropulsion system predicts a maximum lsp of 286 lbf.s/lbm as compared to 267 lbf.s/lbm for carbon--a 7% increase. The .rho.*lsp produced by silicon is 14.5 lbf.s/cubic inch as compared to 13.7 lbf.s/cubic inch produced by carbon--a 7% increase. A 25% solid loading in solid fuel-gas generators for the hybrid rocket produced a maximum lsp of 278 lbf.s/lbm as compared to 267 lbf.s/lbm produced by carbon--a 4% increase. The .rho.*lsp produced by silicon is 14.8 lbf.s/cubic inch as compared to 14.1 lbf.s/cubic inch produced by carbon--a 5% increase. Another advantage for silicon loaded gel fuels is the large 'plateau' in the performance versus oxygen/fuel curves, and, resulting in a less stringent oxidizer-to-fuel ratio (O/F) control in an operational system.

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Madison, AL, United States of America

Darren M Thompson