US3067074A - Slow burning propellant composition - Google Patents

Description

tates te 3,07,074 Patented Dec. 4, 1062 Free SLOW BURNHNG PRGPELLANT COMPOSITION William A. Gey, China Lake, Califl, assignor to the United States of America as represented by the Secre= fan of the Navy No Drawing. Filed Oct. 16, 1958, Ser. No. 767,752

1 Claim. (Cl. 149-19) (Granted under Title 35, US. Code (E52), sec. 266) The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to gas generating compositions; more specifically it relates to a source of gas to act as a source or" power rather than to rocket propellants.

Many present day guided missiles require a source of power to activate circuits in the guidance systems, and usually the power is provided by a gas-driven turbine or piston operated device.

The gas used must be free of solid particles which would foul the turbine blades or clog the small conduits through which gas travels from the gas generator to the piston cylinder. Accordingly, the designer must either provide a filter if solid particles are present in the gas, or else choose a composition which will produce gas free of solid particles.

Both choices have been made in the past; both have certain disadvantages. Filters are apt to clog and the compositions which producedino solid particles, usually of the double-base variety, did not exhibit good stability on long storage.

A gas generator such as'the one contemplated in this invention must be relatively slow burning as compared to a propellant. Burning rates are dependent upon chamber pressure and it is desirable from a design standpoint to have compositions which have burning rates of from 0.05 to 0.25 inch per second at pressures of from about 400 p.s.i. to about 3000 p.s.i.

It is also important that the composition have a pressure exponent not greater than 0.7. Burning rates of gas generators usually follow the relationship: r=cp where r=burning rate, p chamber pressure, and c and n are constants characteristic of the composition. It is the pressure exponent and it is readily apparent from the equation that high values of n give rapid changes of burning rate with pressure, which is undesirable.

. it is therefore an object of this invention to provide gas generator compositions which produce only gas and no solid particles which have good stability on long storage.

Another object is to produce such compositions as aforementioned with burning rates within the range of from about 0.05 to about 0.25 inch per second at pressures ranging from about 400 p.s.i. to about 3000 p.s.i.

Still another object is to provide gas generating compositions having pressure exponents of burning less than 0.7 in addition to the aforementioned advantages.

Other objects and features of the invention will become apparent to those skilled in the art as the disclosure is made in the following detailed description.

The invention consists in making a composition consisting of a finely ground oxidizer, a polymerized alkene which contains more than 50% halogen, and wax in the proper proportions so that the combustion products are entirely gaseous and consist of carbon monoxide, hydrogen fluoride, hydrogen chloride, hydrogen, and nitrogen.

The oxidizer is preferably ammonium perchlorate but ammonium nitrate may be used as well, as both these oxidizers produce only gases on decomposition.

The polymerized alkene may be any solid straight chain compound and may contain more than one double bond. However, at least 50% of the weight of the compound must be due to halogens substituted on the chain. Fuorine is preferred over the other halogens as it gives combustion products of lighter molecular weight than the others. The alkene preferred is polychlorotrifiuoroethylene having a molecular weight ranging from about 4000 to about 6000. This alkene is known in commerce as Kel-F 200 and is readily available.

The wax employed in the composition may be any solid parafiin and its function is to provide enough hydrogen to form hydrogen halide and also to promote the formation of carbon monoxide rather than carbon dioxide.

The compositions are made by placing the ingredients in a vessel, warming the vessel to about C., stirring the melt to insure homogeneity, and allowing the melt to cool.

The compositions are formed into grains by breaking up the melt into small chunks. These chunks are put into a warmed extruder and forced through a die into any shape desired.

Presented below in Table I are several specific examples of formulations and their properties though the invention is by no means limited to such. All percentages shown are by weight.

Table I Example Composition and Properties Ammonium Perchlorate, percent 50 49. 6 4S. 7 Polychlorotrifiuoroethylene, percent 50 49. 2 48. 3 Paraffin Wax, percent 0 1. 2 1. 9 Burning Rate, in./sec.:

600 p.s.i. 0.135

1,000 p.s.i. 0. 26 0.17 0. 31

3,000 psi 0. 25 Pressu'e Erponent 0 5i Heat of Explosion, caL/g With no parafl'm the burning rate is just about as high as designers will usually tolerate. As paraffin is added, the burning rate goes down, reaches a minimum, and then goes up. At a paraffin content of 1.9% the burning rate is rather high, but the composition would be useful for certain applications. The proportions of oxidizer and polymer are substantially equal by weight with a slight excess of oxidizer. The critical composition range is from about Zero to about 2 weight percent of paraflin wax and the remainder oxidizer and polymer in a weight ratio of about 1 to l.

The data in Table I was obtained by standard techniques. Burning rate data was obtained by coating a strand of material with an inhibitor such as polyvinyl chloride or polyvinyl alcohol, drilling two small holes in the strand exactly two inches apart, connecting wires in the holes with appropriate timing devices, and burning the strand in cigarette fashion under given pressures of nitrogen.

Heats of explosion were obtained using well known calorimetric techniques.

The combustion products of the above compositions were entirely gaseous with no noticeable formation of solid particles. The above results show that a composition has been produced for use as a gas generator fuel which has an acceptable burning rate within the required 3 4 pressure range and which forms no solid combustion References Cited in the file of this patent products.

Obviously many modifications and variations of the UNITED STATES PATENTS present invention are possible in the light of the above 2,783,138 Parsons 1957 teachings. It is therefore to be understood that within 5 2,857,258 Thomas 1958 the scope of the appended claim the invention may be OTH R REFERENCES practiced otherwise than as specifically described. kt Propulsion Air Technical service command 1946 What is claimed is: p 151 A relatively Slow burning gas generating composition Zaehrin er Solid Propellant Rockets Second Sta e msisfing of up to about 2% Paraffi and about 10 American Rdcket Co BOX 1112 Wyandotte Michigan equal parts ammonium perchlorate and polychlorotri- September 1958 pp 1 fluoroethylene, said percentages being by weight.