US3116187A - Gelled nitric acid rocket propellant containing silica gel - Google Patents

Description

nite States The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to us of any royalty there- This invention relates to rocket propellants and more particularly concerns new compositions of matter having gelled or grease-like structures comprising silica gel and rocket fuels and/ or oxidizers.

Rocket fuels and oxidizers, in liquid form among others, are currently employed as propellants in space vehicles. It is desirable under some types of operating conditions to employ the liquid materials in a solid, grease-like or semi-solid form. For example, when gelled materials are used, the seal problem inherent in liquid propellant rockets and missiles is eliminated, and hence, such vehicles could be fueled a considerable period in advance. The gelled material lends itself to easy pumping and further, the foaming problem is not encountered when gelled materials are pumped through small orifices as are liquids.

Heretofore, gelling agents for liquid fuels and oxidizers have been known in the art, but in general, have failed to meet the stringent requirements of rocket and missile devices. For the most part, known gelling agents have been inadequate in that gels could not be formulated from liquid hydrocarbons, for example, of diverse boiling ranges and/ or diverse compositions by simple stirring or mixing of the gelling agent at ambient temperatures. They have been unsatisfactory for the additional reason that their rate of gelling hydrocarbon liquids is greatly affected by the temperature of admixing. Also, they were not capable of forming satisfactory gels within a reasonable time when reasonable amounts are added to such hydrocarbon mixtures as aviation fuels containing substantial amounts of isooctane.

Nitrocarbons are also commonly employed as propellant. Up to now, difiiculty has been encountered when an attempt was made to produce gels from the various liquid nitrohydrocarbons, and particularly nitroparafiins, without seriously aifecting the oxygen balance and otherwise changing their properties.

The present invention overcomes these and other difiiculties involved in gelling liquid fuels and oxidizers by providing compositions comprising liquid propellants which are gelled by minor additions of finely divided silica gel, said gels retaining their consistency for long periods of time without undergoing deleterious changes in properties.

It is therefore a primary object of this invention to provide a gelled or grease-like composition comprising minor proportions of a gelling agent which may be incorporated into a wide variety of liquid fuels and oxidizers by simple mixing or stirring at ambient temperatures.

Another object of the invention is to provide compositions whereby a gelling agent is incorporated into a wide variety of liquid fuels and oxidizers to produce stable gels for rocket and missile propellants.

An additional object of the invention is to provide compositions of gelled fuels and oxidizers which have incorporated therein a gelling agent which is inexpensive, readily available and easy to use; and wherein the resulting composition is not susceptible to premature breakdown with concomitant loss of viscosity.

Other and further objects of the invention will be apparent to those skilled in the art upon study of this disclosure.

Various liquids and liquid combinations have been found useful as rocket propellants. Some propellants consist of a single material, and are termed monopropellants. Those propellants involving two materials are termed bipropellants and normally consist of an oxidizer and a fuel.

Nitromethane, among others, is a well known mono- -propellant. Well known bipropellants include hydrogen peroxide or liquid oxygen as the oxidant with a fuel component such as ethanol-water, ammonia, hydrazine, or hydrogen; and nitric acid as the oxidizer with aniline or alcohols as the hypergolic fuel component.

When employing a concentrated white fuming nitric acid, e.g., having a concentration in the neighborhood of about to as the oxidizer in a rocket propellant, it is often necessary, dependent on the specific fuel component, to make ignition more prompt by dissolving minor proportions of nitrogen dioxide in the white fuming nitric acid, thereby forming red fuming nitric acid.

Other fuels such as alkyl nitrates, of which ethyl, propyl and butyl nitrates are the most common, and nitroparaffins, such as nitromethane, and nitroethane, may be readily gelled in accordance with the compositions claimed by this invention. Alcohols, such as ethanol, propyl alcohol and butyl alcohol, and hydrazines, for example, monomethyl hydrazine, and combinations including hydrazine and ethylene diamine, hydrazine and alcohols as aforementioned, hydrazine and ammonia, with unsymmetrical dimethyl hydrazine, and unsymmetrical dimethyl hydrazine with diethylene triamine have also been found amenable to gellation in accordance with the compositions of the present invention. Mixtures or blends of any of the aforedescribed alkyl nitrates and alcohols, of nitroparaffins with alkyl nitrates and/or alcohols; and alcohols mixed with nitroparafiins, aniline and hydrazine; and amines, such as diethylene triamine, NNNN-tetramethyl-butane-l,3-diamine, trimethylamine and aniline; and hydrocarbons such as isooctanes have also been successfully gelled as claimed herein.

Finely divided, inorganic, commercially available silica gel is used as the sole gelling agent. The material is cheap and easy to use. Three to five weight percent of this material is slowly added to any of the liquid fuels, fuels and oxidizers, or any of the prescribed operable combinations thereof, at room or ambient temperature, the liquid being stirred during addition. The stirring may be accomplished by hand, or optionally, if larger amounts are involved, by any suitable or conventional mechanical stirrer or agitator. The stirring operation is normally performed within 1 to 2 minutes, no further agitation being necessary thereafter. At the upper limit of silica gel addition, i.e., about 5%, the liquid may partake of a semi-grease-like structure, or thick gel, while further additions up to about 8% will progressively result in the formation of a grease-like compound. The gelled or grease-like compositions have been found to remain stable and yet retain their approximate viscosity for periods upwardly of six months, under usual military storage conditions.

By way of further explanation, some specific examples illustrating the invention will hereinafter be described. This is done solely by way of example and is intended neither to delineate the scope of the invention nor limit the ambit of the appended claim:

Example I Ninety-six pounds of monomethyl hydrazine was contained in a suitable vat and agitated mechanically. Four Kr pounds of finely divided silica gel Was poured slowly thereinto consuming about 30 seconds, the agitation continuing throughout. Agitation Was further continued for about 90 seconds, the entire operation'being performed at 78 F. A stable gelled fuel resulted.

Example II Twenty-three pounds each of propyl nitrate and nitroethane were mixed for 30 seconds until the compounds were thoroughly blended. While the mixing continued 3.8 pounds of finely divided silica gel was slowly added thereintq. Additional agitation for approximately 60 seconds at 75 F. produced a stable gel composition having the characteristics desired for rocket propellants.

It is apparent that we have provided a wide variety of rocket propellant compositions in gelled, semi-grease or grease-like forms and depending only upon the amount of gelling agent employed. The resulting compositions are stable, exhibiting shelf lives upwardly of six months without undesirable settling out or loss of viscosity. An

important feature of the present invention resides in the small proportions of gelling agent necessary for any of the prescribed materials discussed hereinabove, i.e., a minimum of about 3 weight percent of agent ordinarily produces a gel-like compound While increasing the silica gel content to about 8 weight percent results in a grease- References Cited in the file of this patent UNITED STATES PATENTS 2,891,852 Schaad June 23, 1959 2,902,351 Stokes Sept. 1,1959 2,922,703 Bauer Jan. 26, 1960 3,035,950 Long -c May 22, 1962 3,077,072 Rice Feb. 12, 1963 OTHER REFERENCES Zimmerman et al.: Handbook of Material Tradenames, Supplement II, p. 40 (1957), Industrial Research Service Inc., Dover, New Hampshire.