US2944385A - Stable monopropellants - Google Patents

Description

m ahes tures as needed, up to about 20% by weight.

STABLE MONOPROI ELIJANTS Emory E. Toops, Jr., Terre Haute, 1nd,, assignor to Commercial Solvents Corporation, Terre Haute, Ind, a corpor'ation of Maryland No Drawing. Filed May 19, 1958, Ser. No. 735,920 Claims. c1. 60-354 My invention relates to new propellants for reaction motors, and more particularly, to propellant mixtures of lithium chlorate in ammonia.

The missile industry has been unable to formulate a stable, non-corrosive, relatively insensitive monopropel lant which can beeasily stored and handled without endangering the 'lifeand health of personnel working in the area. Compounds such as ethylene oxide nitromethane,"tetranitromethane, propyl nitrate,etc. have found some use as monopropellants in reaction motors. There hasbeen no wide acceptance of these materials as monopropellants, due to the extreme shock sensitivity or reactivity inherent in these products.

I have now discovered that solutions of lithium chlorate in ammonia are excellent monopropellants and fuels. As the oxygen balance of my new lithium chlorate-ammonia solutions can be varied over a wide range, my compositions find a variety of uses in'the propellant field. Some of my new compositions, having a high ratio of reducing potentials to oxidizing potentials, are useful as fuels for air-breathing engines, such as pulse jets and tems; while my solutions having approximately equal res Patent 0 perchlorate, etc.

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' tures include hydrazine; metals such as aluminum and magnesium; boranes; alcohols such as methanol and ethanol; etc. Additives which I have found useful in adding oxidizing potentials to my compositions include nitrosyl fluoborate, monomethylamine nitrate, monomethylamine Water may be added to my composition to increase the volume of the combustion products formed and to decrease the burning temperatures of my compositions.

Oxidants" which may be utilized withmy fuel mixtures in bipropellant systems are any of the commonly used oxidants, such as liquid oxygen, red'and white fuming nitric acid, dinitrogen tetroxide, etc.

My new compositions'have specific impulses of about 210, on the order'of some commonly used liquid bipropellant systems, while being relatively economical to prepare. As my propellant solutions h'averelatively high densities; on 'the order of 1.3 or more, they have impulse densities in excess of 280. .7

My new lithium chlorate-ammonia mixtures are rela- Y tively non-corrosive to cold rolled.v steel and'aluminum ratios, of oxidizing potentials to reducing potentials are excellent in'onopropell-ants in that theyfare thermally stablev and relatively insensitive to shock resulting "from induced'pressuresorimpact. Y I It is known that ammonia will salts. It is also" known that most oxidant salts are too insoluble in ammonia to form mixtures suitable for use as monopi'opellants. No ammonia-oxidant 'salt mixtures are known which have oxygen balances such that the systems couldbe used as liquid monopropellants. ,Known mixtures are exemplified byDive'rs solution, which is' so diflicult to. burri'that it cannotlbe'lused as a-mpn'opropellan t. Unexpectedly, Ih'a've found' that ammonialithium chlorate-mixtures, having suitable oxygen balances," .have very rapid burning rates. and low, ignition temperatureswhen compared with other ammonia-oxidant salt solutions, andas a result, are excelle'nt mono dissolve many oxidantwith lithium chlorate, ammonia or other additives at ordinary storagev temperatures and pressures in such a manner as to reduce materially the desired explosive or propellant properties of themixtures. The inert addltives may be introduced'intomy mixtures to sensitize or desensitize the compositions, to add oxidizing or reduc- ,ing potentials to the compositions, to. catalyze the burnetc.

The compositions'of my invention have very low vapor pressures, on the order of about 5 pounds at 25 C..

The compositions of my invention cancontain from about 2 to about 3 moles of ammonia per mole of lithium;

chlorate. A solution containing two moles of ammonia and one mole of lithium chlorate is in exact oxygen balance. However, slightly better performance is obtained when the propellant solution is slightly fuel-rich.

My new compositions are prepared by passing anhydrous ammonia into the solid lithium chlorate salt. I prefer to prepare my compositions at temperatures below, the boiling point of, anhydrousammonia, due to ease 'of handling.

My compositions. are easily adapted to a variety of uses in the propellant'field. My?- compositionshav-ing reducing potentials in the rangeof 5 to 15% inexcess v of the oxidizing potentials are excellent monopropellants.

Solutions'thatare very fuel rich,'containing from :20 to 40%-.excess reducing potentials are useful as bipropellant fuels in rockets or fuels for ramjets, etc.

'To' utilize the. propellant solutions of my invention, I

introduce them, at adesired rate, into a reactionichamber containing a suitable igniter, such as a starting s'quib or a white hot platinum grid, to initiate combustion. Once combustion has begun, theheatin'g element can here- 5 moved, or, in the case of platinum heaters, canremain within the reaction-motor to catalyze the burning rate ofthe propellanti' I 5 e As previously stated, compositions containing from 20 to 40% excess reducing potentials are useful as fuels for reaction motors such as ramjets and as fuels for bipropellant rocket systems. The use of such mixtures as fuels for bipropellant systems means that less oxidant is required as the high specific gravity fuel carries considerable amounts of oxygen.

When my compositions are used in air-breathing engines, such as ramjets or pulse jets, principles of operation which apply are similar to those' applicable to present day engines employing ordinary hydrocarbon fuels. In all of these engines" the oxygen in the air is mixed with the fuel so thatlthe fuel-air ratio is approximately stoichiometric. In this way, completeburning and efli cient operation of theengine is assured. ;For example,

Patented July 12, 1960 when a 50% lithium chlorate, 50 wt. percent ammonia I mixture isusedas a ramjet engine fuel, a ratio of 1.921. air to fuel by weight is desired. This fuel produces about 1930 B.t.u. per pound of air used While standard hydrocarbon: fuels.- produce only: about 1200-1300 B.t:u. per. pound of air. During: or after combustion of; my. fuels in the combustion chambers of the reaction engines large amountsof excess air are passed through the en'- gines in .order that the combustion chamber walls may be maintained at desired temperatures.

The following tablediscloses the physical properties; of a representative propellant solution-of my invention. containing onezmole .of lithium. chlorateto twomoles of ammonia. Aspreviously-statedthiscomposition isin oxygen balance.

Density, 25 C V V p 1.35 Specific impulse at 300 p.s.i.a., sec 210 Impulse density, sec 2.83 Viscosity, centipoises at:

25 C 65 20 C; 79 c 122- 0 C 198 l0 C 343 Vapor pressure mmabs. at 25 C 220 The following'table sets out the solubility of various amounts of lithium chlorate in ammonia.

SOLUBILITY OF ANHYDROUS LITHIUM. CHLO- The following specific examples more fully illustrate my invention, but it is not intendedthat my invention be limited to the processes, reaction motors or fuels described therein, but rather it is intended that all. equivalents obvious to those'skill'ed in the art be included within the scope of my invention as claimed.

' Example I I To test one of my compositions as a monopropellant 0.18 pounds per second ofa. 2:1 molar ratio of monomethylamine to lithiumv chlorate was injected: into a small rocket thrust chamber. through four converging injection nozzles. This propellant burns well and has a.

specific impulse of 209 seconds.

Example II To test one'of my propellant compositions in a bipropellant system a small thrust chamber made up of available 1" stainless steel pipe and stainless steel. plpe fittings was prepared. The fuel injection nozzle was made from a pipe plug. A11 orifice diameter of0.04 was drilled in the pipe plug and theneedle valve assembly was seated in and welded onto the plug. For ease of repair a 1'' union was used to attach the nozzle to the 4 pipe which comprises the burning chamber. An oxygen inlet tube and a Bourdon-type pressure gauge with a range of 0-600 p.s.i. were attached to the burning chamber through the plug. A reducing coupling was utilized aspthe motor nozzle. A reaction mixture having a molar ratio of 3:1 ammonia to lithium chlorate was introduced into the thrust chamber through the injector nozzle at a rate of 0.2 cu. ft. per minute. An approximately stoichiometrically equal amount of gaseous oxygen-was also introduced into the thrust chamber. Ignition was initiated by preheating the chamber to 625 C. The fuel burned Well with good thrust.

This application is a continuation-in-part of my U.S. patent application Serial No. 704,361 filed December; 23, 1957 now abandoned.

Now having described my invention what I claim is:v

1. Monopropellant mixtures consisting essentially of lithium chlorate-ammonia mixtures having a molar ratio, of lithium chlorate to ammonia ranging from about 1:2 to' about 1 3, and an inert additive selected from the group consisting of lower alkyl alcohols, water, monomethyk amine nitrateand monomethylamine perchlorate.

2. Monopropellant mixtures consisting essentially of lithium chlorate-ammonia mixtures containing a ratio Off 11 mole of lithium chlorate to about 3 moles of ammonia; and up to 0.25 mole of water per mole of ammonia.

3. In a process for producing thrust-in a reaction motor which comprises burning, in a reaction motor, mixtures having a molar ratio of lithium chlorate to ammonia ranging from about 1:2 to about 1:3.

4. The process forproducing thrust in a monopropellant burning reaction motor which comprises burning, in a monopropellant burning reaction motor, a mixture of'lithium chlorate in ammonia, said mixture having a molar ratio of 2.5:1 ammonia to lithium chlorate.

5. The process for producing thrust in a bipropellant burning reaction motor which comprises burning, in a bipropellant burning reaction motor, mixtures having a molar ratio of lithium chlorate to ammonia ranging from. about 1:2 to about 1:3 and -a bipropellant oxidant selected; from the group consisting of liquid oxygen, redand white fuming nitric acid and dinitrogen tetroxide.

References Cited in the file of this patent UNITED STATES PATENTS 1,506,323 ONeill Aug. 26, 1924 2,393,594 Davis Jan. 29, 1946 2,811,431 Zwicky et al Oct. 29, 1957' OTHER REFERENCES

Claims (1)

1. 5. THE PROCESS FOR PRODUCING THRUST IN A BIPROPELLANT BURNING REACTION MOTOR WHICH COMPRISES BURNING, IN A BIPROPELLANT BURNING REACTION MOTOR, MIXTURES HAVING A MOLAR RATIO OF LITHIUM CHLORATE TO AMMONIA RANGING FROM ABOUT 1:2 TO ABOUT 1:3 AND A BIPROPELLANT OXIDANT SELECTED FROM THE GROUP CONSISTING OF LIQUID OXYGEN, RED AND WHITE FUMING NITRIC ACID AND DINITROGEN TETROXIDE.