US3146139A

US3146139A - Oxidizer composition comprising nitrogen tetroxide, tetranitromethane and nitromethane

Info

Publication number: US3146139A
Application number: US78180A
Authority: US
Inventors: John O Collins; Stephen P Terpko
Original assignee: Callery Chemical Co
Current assignee: Callery Chemical Co
Priority date: 1960-12-23
Filing date: 1960-12-23
Publication date: 1964-08-25
Anticipated expiration: 1981-08-25

Description

GIZER COMPGSITION COMPRISING NITRO- GEN TETROXKDE, TETRANHTRGMET AND NHTROMETHANE John 0. Collins, Eau Claire, Win, and Stephen P. Terpko,

Winchester, Mass, assignors to Callery Chemical Company, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Filed Dec. 23, 1960, Ser. No. 78,180

4- Claims. (Cl. 1491) This invention relates to new and useful liquid oxidizer mixtures for rocket propellant applications and in particular it relates to binary and ternary mixtures having improved properties.

The expression propellant is generally used to refer to those materials which release chemical reaction energy and/ or generate gases necessary to serve as working fluid in thermodynamic expansion. Propellant components are those materials which are the constituents of the propellant and may be further classified, according to their contribution in the propellant reaction, as fuels, oxidizers, and additives. The latter usually serve to control or modify propellant characteristics and properties including burning rates, storage stability, ignition properties, and freezing and boiling points. Propellants which are self sufiicient without requiring additives are, in general, to be desired since such additives usually detract from the propellants specific impulse although otherwise desirable for the correction of particular deficiencies in the propellant.

There are several liquid oxidizers now used in rocket propulsion, most common of which are liquified oxygen, fuming nitric acid and hydrogen peroxide. These oxidizers have some physical and chemical properties which are undesirable. Thus, an extensive search has been made to find liquid oxidizer mixtures having the best compromise of the following properties: high density, a liquid temperature range to include ambient conditions, low viscosity at operating temperature, stability to mechanical and thermal shock, stability during storage, non-corrosiveness, little or no toxicity, economy of production, ease of ignition and high specific impulse with common fuels. Mixtures which meet most of these ideal requirements have now been found and are described hereinafter.

In rocket propellant considerations ambient temperature refers to the temperature of the rocket launching site, the place of propellant usage. This may vary from the tropics to the Arctic-a possible range of from above 40 C. to below 40" C. Special heating or refrigeration installations are eliminated with liquid propellant components which remain liquid at ambient temperature. Hydrocarbon or hydrocarbon derivative fuels, the commonly used liquid fuels, possess a liquid range broader than the extremes of ambient temperatures encountered. However, many of the liquid oxidizers of actual or poten tial application in rocket propulsion offer many problems in the maintenance of the liquid state at these ambient temperatures. Liquid oxygen, for example, must be refrigerated under any condition of use.

It is an object of this invention to provide new and improved liquid oxidizer mixtures for rocket propellant applications.

Another object is to provide completely miscible liquid binary and ternary oxidizer mixtures formulated from nitrogen tetroxide, tetranitromethane, and nitromethane which have a wider liquid range than nitrogen tetroxide alone and are stable against oxygen evolution.

A further object is to provide additives for liquid oxidizers for propellant systems which do not detract from the propellants specific impulse.

Other objects will become apparent from the specification and appended claims.

These new and improved liquid propellant oxidizer mixtures will be more fully described hereinafter and the novelty thereof will be particularly pointed out and distinctly claimed.

, This invention is based upon the discovery that the addition of nitroparaffins such as nitromethane and tetra-.

nitromethane to nitrogen tetroxide will lower both the freezing point and vapor pressure of the latter without substantially reducing the specific impulse attainable when used with typical hydrocarbon fuels. The binary and ternary mixtures remain liquid over a wider temperature range than nitrogen tetroxide alone but still possess high oxidizing power and are much more stable. It has also been discovered that nitromethane and nitrogen tetroxide form binary and ternary mixtures with tetranitromethane to dramatically lower the freezing point of the latter to produce a stable highly oxidizing propellant component.

Nitrogen tetroxide itself is a good oxidizer but it has an extremely narrow liquid range, melting at 9.3 C. and boiling at 213 C. Tetranitromethane, another good oxidizer, freezes at 13.8 C., which is too high for usual liquid propellant applications, and boils at 125.7 C. Nitromethane melts at -28.6 C. and boils at 101.3 C. Thus, we have discovered that these two good oxidizers, nitrogen tetroxide and tetranitromethane, can be sub stantially improved in properties by intermixing these to form binary mixtures and/ or intermixing these with nitromethane to form binary and ternary mixtures.

In an effort to improve the liquid range of nitrogen tetroxide with additives, it was discovered that tetranitromethane and nitromethane were compatible with nitrogen tetroxide, forming one liquid phase in all proportions without evolution of oxygen, and most significantly it was discovered that a wide range of useful oxidizer compositions with varying properties could be obtained from suitable mixes of these substances.

Thus, it was discovered that the very narrow liquid range of nitrogen tetroxide of only 30L6 C. could be broadened and varied by the addition of different quantities of tetranitromethane and nitromethane. As either of these materials are added to nitrogen tetroxide the boiling point of the mixture increases. For example, the binary mixture of nitrogen tetroxide with tetranitromethane (mol percentage of N 0 stated) boils at 30 C. with about 60 mol percent, at 40 C. with about 44 mol percent, at 50 C. with about 34 mol percent, and at 60 C. with about 27 mol percent. A smaller molar quantity of tetranitromethane is required to raise the boiling point of nitrogen tetroxide a specific amount than is required of either nitromethane or a mixture of tetranitromethane and nitromethane. Thus, both a composition containing about 36 mol percent N 0 and 64 mol percent CH NO and a composition of 36 mol percent N 0 32 mol percent C(N0 and 32 mol percent CH NO boil at about 40 C. In addition to the compositions containing nitrogen tetroxide described above, we have discovered that mixtures of tetranitromethane and nitromethane are uniformly high boiling with the lowest boiling mixture of the two being 92 C. occurring at the azeotrope containing about mol percent nitromethane.

In reducing the freezing point of nitrogen tetroxide it was found that the lowest temperature that could be arrived at with tetranitromethane as the additive was 30" C. the freezing point of the eutectic containing 59 mol percent of N 0,. In order to further reduce the freezing point nitromethane must be added. For example, we have discovered that the most oxygen rich ternary mixture freezing at 40 C. contains about 53 mol percent N 0 25 mol percent C(NO and 22 mol percent CH NO while the most oxygen rich ternary mixture freezing at 50 C. contains about 47 mol percent N 0,, 19 mol percent C(NO and 34 mol percent CH NO Patented Aug. 25, 1964 3 These two ternary mixtures will boil at 33 C. and 35 C. respectively. Still lower freezing points can be obtained at or near the two eutectic compositions indicated below:

Whether nitrogen tetroxide or tetranitromethane is an additive to the other is not significant, since in either case the resulting mixture will be a good oxidizer with improved properties. However, nitromethane is considered solely as an additive although it may be present in significant amounts. For oxygen availability it has been found desirable to limit the amount of nitromethane in any binary or ternary mixture to about 70 mol percent and it is preferred that it be below this amount. Significantly the properties ordinarily desired may be obtained with lesser amounts of nitromethane and in some uses it is entirely absent. Additionally it is preferred, although it is not a necessity, that the amount of any constituent, when present, be at least 5 mol percent so that it may produce a significant beneficial efiect on properties.

As described herein it is possible to obtain specific compositions which are usable over a wide range of ambient conditions by incorporating together in suitable proportions any two or three of the compoundsnitrogen. tetroxide, tetranitromethane, and nitromethane. If highly oxidative compositions are desired, nitrogen tetroxide, tetranitromethane and nitromethane are utilized in the order named. If high boiling mixtures are required, compositions containing tetranitromethane, nitromethane and/ or nitrogen tetroxide, listed in the order of effectiveness, are formulated. If a low freezing point is desired, mixtures containing nitromethane, nitrogen tetroxide and/or tetranitromethane, listed in the order of effectiveness, are formulated; however, as already indicated it is only possible to go below 37.5 C. with binary or ternary mixtures containing both nitrogen tetroxide and nitromethane. Thus it is seen that each compound makes its own special contribution to the mixture permitting a great variety of completely miscible mixtures of oxidizers to be formulated. General all purpose oxidizer mixtures can be made on the one hand and special purpose oxidizers on the other, all

4 having superior physical properties over the individual constituents and being stable against oxygen evolution.

Since tetranitromethane and nitrornethane contain a hydrocarbon group which acts as a fuel in the propellant combustion, the greater the proportion of these materials that are present in the oxidizer component, the less fuel component is required for the propellant. When the fuel component is a hydrocarbon there is no material overall effect on the specific impulse of the propellant resulting from the introduction of fuel elements with the oxidizer. However, when the fuel is a higher performance fuel, it is preferred to use oxidizer mixtures of our invention having a higher oxidizing potential.

This application is a continuation-in-part application of our application field July 8, 1955, Serial Number 520,917, now abandoned.

According to the provisions of the patent statutes we have explained the principle and mode of practicing our invention and have described what we now consider to be its best embodiments. However, we desire to have it understood that, within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I We claim:

1. A liquid oxidizer composition for use in rocket propulsion which consists essentially of a mixture of from about 33 to about mol percent nitrogen tetroxide, from about 5 toabout 41 mol percent tetranitromethane, and from 0 to about 56.5 mol percent nitromethane.

2. A composition according to claim 1 in which the concentration of nitrogen tetroxide is about 33 mol percent, the concentration of tetranitromethane is about 10.5 mol percent, and the concentration of nitromethane is about 56.5 mol percent.

3. A liquid oxidizer composition for use in rocket propulsion which consists essentially of about 59 mol percent nitrogen tetroxide and about 41 mol percent tetranitromethane.

4. A liquid oxidizer composition for use in rocket propulsion which consists essentially of a mixture of from about 33 to about 95 mol percent nitrogen tetroxide, and from about 5 to about 41 mol percent tetranitromethane.

References Cited in the file of this patent UNITED STATES PATENTS Morrow Aug. 15, 1944 Hannum Feb. 5, 1952 OTHER REFERENCES

Claims

1. A LIQUID OXIDIZER COMPOSITION FOR USE IN ROCKET PROPULSION WHICH CONSISTS ESSENTIALLY OF A MIXTURE OF FROM ABOUT 33 TO ABOUT 95 MOL PERCENT NITROGEN TETROXIDE, FROM ABOUT 5 TO ABOUT 41 MOL PERCENT TETRANITROMETHANE, AND FROM 0 TO ABOUT 56.5 MOL PERCENT NITROMETHANE.