Gas Generating Composition

There are many applications which require a storable source of gaseous nitrogen which may be used for a variety of pressurization or purging applications, for example. Nitrogen is inert with respect to many oxidizers, including the high energy interhalogen compounds such as ClF.sub.3 and ClF.sub.5, fluorine, oxygen, or various nitric acid compositions such as red fuming and white fuming nitric acid and many fuels such as hydrogen, hydrazine, kerosene, or other hydrocarbons. Thus, in rocket motors for example, it is possible to use nitrogen to pressurize or purge both fuel and oxidizer tanks. Nitrogen is also used in space station and vehicle atmospheres as a diluent for the oxygen. Thus, in the event of leakage not only will oxygen but also nitrogen will be lost and a storable means of replenishing nitrogen in the event of leaks is required. Nitrogen gas is also used in many laser applications and a storable source of gaseous nitrogen would be highly desirable, particularly for portable and military operations. In laser applications for example, it is also desirable that nitrogen contain amounts of other gases such as carbon dioxide, carbon monoxide or water.

There are three basic ways of storing nitrogen, i.e., as a gas, as a liquid, or chemically combined in a manner in which it can be controllably released. Storage as either gas or liquid is done by state-of-the-art techniques, but is associated with the problems inherent to pressurized gases or cryogenic liquids. A substantial body of art, therefore, has been developed towards making so-called nitrogen "candles" which are combustible compositions capable of liberating gaseous nitrogen. Such a composition is represented by U.S. Pat. No. 2,981,616 to Boyer for a Gas Generator Grain. The composition of this patent utilize a metal azide as a source of the nitrogen and an amount of oxidizing agent selected from the class of metal peroxides, inorganic perchlorates and metal nitrates in amounts sufficient to fully oxidize the metal component of the azide. Such compositions are capable of producing nitrogen gas, however, they are relatively energetic systems which can present safety hazards from inadvertent ignition. Further, these oxidizing agents produce high flame temperatures in the combustion process and in many cases the nitrogen gas evolved must be subsequently treated to cool it to a usable temperature and in some cases the temperature may also be so sufficiently high as to produce volatilization of some of the normally solid reaction products.

According to this invention, novel gas generator compositions have been discovered which have substantially no impact or friction sensitivity and which produce nitrogen gas or nitrogen mixed with other gases as the only volatile products at relatively low flame temperatures.

The desirable features of this invention are obtained by reacting metal azides with various metal oxides and salts as the oxidative reactant. To permit self-sustained combustion, the metal forming the azide should be sufficiently above the metal of the oxide or salt in the electromotive series of the elements so that the metal of the azide is capable of exothermically replacing the metal of the oxide or salt. To prevent the liberation of volatiles, other than the desired gases, the metal oxide or salt must be selected such that the residue produced by the reaction consists only of materials which are non-volatile under the reaction conditions. The general reaction sequence may be shown as follows: metal.sub.1 azide+metal.sub.2 oxide (or salt).fwdarw.metal.sub.1 oxide(or salt)+metal.sub.2 +nitrogen

In the above reaction metal.sub.1 is a metal which is higher in the electromotive series of the elements than metal.sub.2 and is capable of replacing the metal.sub.2 exothermically in the above general reaction scheme and the stoichiomety of the system is preferably adjusted to permit maximum liberation of the nitrogen of the azide and of metal.sub.2 together with the total substitution of metal.sub.1 in the oxide or salt.

The addition of a hydrogen-free carbon compound and an oxidizing agent for the carbon in amounts sufficient to convert desired amounts of carbon monoxide to carbon dioxide may be made to the compositions of this invention to permit the generation of nitrogen - CO.sub.2 mixtures for use in lasers. Suitable carbon compounds include, without being limited to, carbonates, metal oxalates such as Li.sub.2 C.sub.2 O.sub.4, Na.sub.2 C.sub.2 O.sub.4, and MgC.sub.2 O.sub.4 and carbon-nitrogen compounds such as tetracyanoethylene (C6N.sub.4).

Elimination or reduction of the additional oxidizer will result in the evolution of carbon monoxide. Addition of hydrated materials or basic oxides such as Mg(ClO.sub.4).sub.2.6H.sub.2 O, FeO.sub.2 H, oxamide and oxalic acid dihydrate either alone or in conjunction with the carbon compound will generate water. The formulas for oxamide and oxalic acid dihydrate are respectively (CO.NH.sub.2).sub.2 and (COOH).sub.2.2H.sub.2 O.

Representative theoretical chemical reactions by which these gases may be generated are set forth below: NITROGEN GENERATORS 6NaN.sub.3 + Fe.sub.2 O.sub.3 .fwdarw. 3Na.sub.2 O + 2Fe + 9N.sub.2 12NaN.sub.3 + 3SiO.sub.2 .fwdarw. 6Na.sub.2 O + Si.sub.3 N.sub.4 + 16N.sub.2 6LiN.sub.3 + B.sub.2 O.sub.3 .fwdarw. 3Li.sub.2 O + 2BN + 8N.sub.2 6KN.sub.3 + Fe.sub.2 O.sub.3 .fwdarw. 3K.sub.2 O + 2Fe + 9N.sub.2 4LiN.sub.3 + TiO.sub.2 .fwdarw. 2Li.sub.2 O + Ti + 6N.sub.2 3NaN.sub.3 + 3LiCl.fwdarw. Li.sub.3 N + 3NaCl + 4N.sub.2 6NaN.sub.3 + 2AlF.sub.3 .fwdarw. 6NaF + 2AlN + 8N.sub.2 3NaN.sub.3 + 3LiF.fwdarw. Li.sub.3 N + 3NaF + 4N.sub.2 6NaN.sub.3 + 3CuCl.sub.2 .fwdarw. 6NaCl + 3Cu + 9N.sub.2 6NaN.sub.3 + Fe.sub.2 (SO.sub.4).sub.3 .fwdarw. 3Na.sub.2 SO.sub.4 + 2Fe + 9N.sub.2 2NaN.sub.3 + FeS.fwdarw. Na.sub.2 S + Fe + 3N.sub.2 2NaN.sub.3 + FeCO.sub.3 .fwdarw. Na.sub.2 CO.sub.3 + Fe + 3N.sub.2 12NaN.sub.3 + 3CaMg(CO.sub.3).sub.2 .fwdarw. 6Na.sub.2 CO.sub.3 + Ca.sub.3 N.sub.2 + Mg.sub.3 N.sub.2 + 16N.sub.2 NITROGEN-CARBON DIOXIDE GENERATORS 6NaN.sub.3 + 9FeCO.sub.3 .fwdarw. 3Na.sub.2 CO.sub.3 + 9FeO + 9N.sub.2 + 3CO + 3CO.sub.2 16NaN.sub.3 + 4SiO.sub.2 + 15MgCO.sub.3 .fwdarw. 8Na.sub.2 CO.sub.3 + Si.sub.4 N.sub.3 + 15MgO + 27N.sub.2 + 7CO.sub.2 2NaN.sub.3 + Fe.sub.2 O.sub.3 + 2FeCO.sub. 3 .fwdarw. Na.sub.2 CO.sub.3 + 4FeO + 3N.sub.2 + CO.sub.2 8NaN.sub.3 + 10FeCO.sub.3 + 2NaNO.sub.3 + 2FeO.sub.2 H.fwdarw. 5Na.sub.2 CO.sub.3 + 2Fe.sub.2 O.sub.3 + 8FeO + 13N.sub.2 + H.sub.2 O + 5CO.sub.2 10NaN.sub.3 + 9MgCO.sub.3 + 0.17Mg(NO.sub.3).sub.2.sup.. 6H.sub.2 O + 1.04 NaClO.sub.4 .fwdarw. 5Na.sub.2 CO.sub.3 + 9.17 MgO + 15.17 N.sub.2 + 4CO.sub.2 + 1.02H.sub.2 O + 1.04NaCl 8NaN.sub.3 + 1.2C.sub.6 N.sub.4 + 0.3(COOH).sub.2.sup.. 2H.sub.2 O + 4.75 NaClO.sub.4 .fwdarw. 4Na.sub.2 CO.sub.3 + 4.75 NaCl + 0.9H.sub.2 O + 3.8CO.sub.2 + 14.4N.sub.2

Table I sets forth the results of tests on various gas generator compositions.

As can be seen by comparing the theoretical reactions and the actual experimental reactions noted in Table I, some differences between the experimental result and the theoretical expectations are observed. For example, in the reaction of aluminum fluoride with sodium azide, the reaction does not proceed to the production of aluminum nitride and sodium fluoride but rather Na.sub.3 AlF.sub.6 and AlN is produced. Also, as can be seen from the above table, it is not always possible to predict which combinations of materials will function properly according to this invention and in what particular relationship they may occur. For example, in the system using lithium azide, aluminum oxide, silicon dioxide, and 1 percent fiberglass reinforcement, no combustion was obtained when the mole ratio of the materials were respectively 12/6/39 and 25/6/90, yet good residue retention was obtained with a mole ratio of 24/6/39. It has not been determined if this was because of the increased amount of sodium azide, decreased amount of silicon oxide or some combination of the two with the latter being the most probable. Thus, while the applicant has not tested every combination of materials in all proportions to determine which do and which do not function to produce a gas generator grain capable of generating nitrogen in self sustained manner at reasonable temperatures, this disclosure is believed adequate to teach workers skilled in the art a new type of composition and how generally to determine which materials will work. Nevertheless, some experimentation, well within ordinary skill, will be required by workers skilled in the art to select the precise composition for any particular combination of materials within the scope of this disclosure and the claims but which are not specifically disclosed by example herein. While this invention has been illustrated with respect to numerous examples, the invention is not limited thereto and various modifications can be made by workers skilled in the art without departing from the scope of the invention which is limited only by the following claims wherein: