WO1992018443A1

WO1992018443A1 - Azide propellant compositions for emergency deballasting of submersible vessels

Info

Publication number: WO1992018443A1
Application number: PCT/US1992/002978
Authority: WO
Inventors: John F. Pietz
Original assignee: Talley Defense Systems, Inc.
Priority date: 1991-04-11
Filing date: 1992-04-10
Publication date: 1992-10-29
Also published as: EP0579781A4; EP0579781A1; JPH06506663A

Abstract

Under emergency conditions such as loss of control or the means of propulsion, a submersible vessel may be deballasted with the use of a plurality of solid fueled gas generators each provided with a propellant composition comprising a blend of an alkali metal azide and an alkali metal nitrate, wherein the ratio of the azide to the nitrate ranges from above stoichiometric to an amount which will result in the production of no more than about 13-14 % by volume of hydrogen in the deballasting gas upon deflagration of the propellant. In an alternate embodiment, a deballasting propellant which forms no hydrogen gas comprises a substantially stoichiometric blend of an alkali metal azide and an alkali metal nitrate, combined with an additive formed of an inert silicon-containing material such as silicon dioxide and a metal oxide, wherein the metal component of the oxide melts at a sufficiently high temperature so as to remain substantially solid during deflagration of the propellant. The additive serves to bind molten particulates produced upon deflagration of the propellant into a solid clinker and thus to prevent this material from passing into the ballast tanks.

Description

AZIDE PROPELLANT COMPOSITIONS FOR EMERGENCY DEBALLASTING OF SUB¬ MERSIBLE VESSELS

Field of the Invention

The invention relates to solid pyrotechnic propellant compositions for emergency deballasting of submersible vessels and more particularly, to blends of alkali metal azides and alkali metal nitrates for use therein.

Background of the Invention

Under normal operating conditions, a submersible vessel, i.e., a submarine, propels itself from its operating depth to the ocean surface in a manner similar to that of an airplane taking off. Adjustable bow and stern planes, which fold out of the way when not needed, permit the vessel to change its depth as required. Once on the surface, the vessel maintains its buoyancy by expelling sea water from its trim tanks with the use of compressed air. This is a relatively simple matter since the only pressure which must be overcome in evacuating water from the trim tanks on the surface is the ambient pressure of the atmospher .

A submersible cruising at a considerable depth, which loses its controls or its means of propulsion is, however, an entirely different matter. Under such circumstances, the vessel can rise to the surface only by expelling sea water from its ballast tanks. In some fleet submarines over 12,000 cubic feet of water must be expelled in order to surface, while in some of the larger vessels, this figure approaches 30,000 cubic feet. Current U.S. submarine deballasting

SUBSTITUTE SHEET systems store a large volume of high pressure (i.e., 4500 psi) air for this purpose. This air is carried by large diameter piping to the main ballast tanks for use in surfacing the vessel under emergency conditions such as those described herein. Although a compressed air system is easily maintained and replenished, it suffers, however, from several important drawbacks as described below. One drawback to the use of a compressed air system is that the thick-walled pressure vessels and distribution piping required to store and transport the high pressure air are bulky and heavy. The estimated total weight of such a system is in excess of 100 tons, with the total volume of the system exceeding 1,000 cubic feet. Moreover, air at pressures in excess of 3000 psi has been observed to behave like pure oxygen, which under certain conditions may pose a fire hazard. Further, at the high external pressures encountered at great depths, stored air becomes less and less effective in expelling water from the ballast tanks because of the effect of gas compressibility factors upon the air. For example, water pressure at a depth of 1,000 feet is approximately 450 psia; to expel one cubic foot of water requires more than 30 cubic feet of air (STP) . At 2,000 feet, more than twice this amount is necessary. Thus, the amount of air which can be carried in the deballasting system serves as a limiting factor on the depth to which the submarine can safely submerge. As deeper-diving designs are contemplated, the drawbacks discussed above take on even greater importance.

The need for an improved emergency deballasting system has thus long been recognized. To this end, various alternative techniques have been studied

SUBSTITUTESHEET and/or evaluated. One method which has been extensively investigated in an effort to reduce the size, weight and complexity of such deballasting systems involves the use of gas generators, which can provide a simple, reliable source of stored energy in place of, or in addition to, a source of compressed air. Gas generators are, in essence, highly efficient energy storage devices which produce gasses by the chemical decomposition of a fuel. An advantage to the use of solid propellant gas generators is that their relatively small size, in contrast to prior art systems which depend upon compressed air to generate buoyancy, permits almost a 2/3 reduction in the weight of the emergency deballasting system.

Gas generators are typically classified as either solid or liquid fueled, as discussed below in turn. One form of solid fueled gas generator whose use in submarine deballasting systems has previously been investigated relies upon rapid, controlled combustion (i.e., deflagration) of a solid fuel mixture to produce large quantities of pressurized gasses. This device is essentially a slow-burning rocket engine designed to produce pressure rather than thrust. Propellants typically utilized with such generators include heterogeneous composites containing a finely divided oxidizer dispersed in a hydrocarbon fuel/binder. The burning rate of these propellants is determined primarily by the chemical composition of the propellant and the exhaust pressure against which it is operating.

A major drawback to the use of such solid fuel gas generators in the deballasting of submersible vessels is that the solid propellant compositions commonly used with these devices generate dangerous gasses, such as hydrogen and carbon monoxide, in

SUBSTITUTESHEET proportions which tend to form explosive mixtures with the air in the ballast tanks, thus rendering these materials impractical for deballasting. Additionally a high proportion of the generated gases are soluble in water, thus rendering them useless and making such compounds inefficient.

One exception is the inorganic azide-based propellants which have been developed for the automobile airbag industry. These materials produce substantially pure nitrogen by the thermal decomposition of sodium azide into metallic oxides and free metals. For example, the combination of stoichiometric amounts of an alkali azide and a metal oxide or an alkali nitrate is known to yield a relatively efficient nitrogen-producing mixture for use in such passive restraints. It is also known, however, that such propellants form a substantial amount of undesirable solid particulates along with the gas. For instance, blending stoichiometric levels of sodium azide and sodium nitrate yields a propellant which, upon deflagration, produces combustion products comprising 55% by weight of nitrogen and 45% by weight of solids. Substituting anhydrous lithium salts for the sodium salts provides a propellant which produces 71% by weight nitrogen with 29% by weight of solids, but lithium salts are extremely expensive and are very difficult to maintain in an anhydrous condition. Airbag propellants have not, however, been previously characterized for discharge against high water pressure, such as that found at normal submarine operating depths. In addition, many of these compositions offer relatively poor yields of buoyant gas per pound of propellant, thus requiring unacceptably high amounts (and weights) of propellant to permit recovery, i.e., surfacing, of a vessel

SUBSTITUTESHEET equipped with a deballasting system utilizing this material.

A second type of solid fueled gas generator produces gas by the rapid oxidation of alkali metals. For example, metallic sodium, lithium and their hydrides react vigorously with water to produce substantial quantities of gaseous products. These products, however, comprise metallic hydroxides and high levels of gaseous hydrogen which, as noted above, can form explosive mixtures when mixed in certain proportions with air.

Turning now to a discussion of liquid-fueled gas generators, liquid propellants for gas generators are classed as either bipropellant combinations or monopropellants. Bipropellants comprise separate fuel and oxidizer sources which are vaporized either through a hyperbolic, i.e., spontaneously igniting, reaction or by the addition of heat. Although bipropellant engines are widely used in missile applications, their complexity, high reaction temperatures and poor performance when operated non- stoichiometrically weigh heavily against their use as gas generators for use in submersible vessels. Monopropellants, on the other hand, contain both the fuel and oxidizer in a single system. They are, in contrast to the bipropellants, relatively simple and operate at substantially lower reaction temperatures than the bipropellant systems. Hydrazine is one monopropellant utilized in several navies for submarine emergency deballasting systems. Hydrazine decomposes spontaneously in an exothermic reaction to form ammonia and nitrogen. Further decomposition of the ammonia in an endothermic reaction on a catalyst bed produces hydrogen and nitrogen in approximately a 2:1 ratio. Formation of

SUBSTITUTE SHEET such a high proportion of hydrogen gas leads, however, to the potential for formation of explosive mixtures of hydrogen and air as discussed above, thus requiring an expensive and complex purging or inerting system. Moreover, hydrazine is itself strongly corrosive, flammable and toxic.

Thus, as described above, although various propellant compositions have been investigated and/or used as substitutes for high pressure air in emergency deballasting systems, none of these propellant materials is capable of completely overcoming all of the drawbacks discussed above to ensure the safe, efficient operation of a submerged vessel under emergency conditions.

Summary of the Invention

It is therefore an object of the present invention to provide solid propellant compositions for use in emergency deballasting systems for submersible vessels.

It is a further object of the invention to provide solid propellant compositions for use in such a system which are safe to handle, transport and which remain reliable after extended periods of storage, including those encountered under submerged operating conditions.

It is an additional object of the invention to provide solid propellant compositions which are capable of producing, upon deflagration, a gaseous product which is non-explosive when mixed with air, non-toxic to personnel who may become exposed to its vapors, non-corrosive to the vessel's ballast tank structure and piping and which will not increase the

SUBSTITUTE SHEET temperature of either the pressure hull or the ballast tank structure itself beyond acceptable limits.

Thus, in accordance with the teachings of the ₅ present invention, a variety of novel nitrogen gas- generating compositions are provided for use in submarine emergency deballasting applications. In a first embodiment, these compositions comprise various blends of alkali metal azide and alkali metal nitrate

_₀ compounds combined in proportions which deviate from stoichiometric levels. These new blends are more efficient gas producers than the stoichiometric mixtures described above. By reducing the amount of the oxidizer, i.e., the alkali nitrate, in proportion

__ to the amount of the alkali azide compound, metallic sodium is produced as one of the combustion products. Exhausting a gas containing this metallic sodium into the water-filled ballast tanks of a submerged vessel causes a reaction which results in the formation of

2₀ hydrogen gas in addition to the nitrogen gas. By carefully controlling the ratio of azide to oxidizer (i.e., the nitrate), a substantially nitrogenous deballasting gas is produced in which the hydrogen component of the gaseous deflagration products is

₂₅ maintained below flammable limits, i.e., below about 13-14% by volume. These ratios may vary within relatively narrow limits depending upon the specific azide/nitrate mixture used. Exhaust gas mixtures having a level of hydrogen below about 13-14% have

₃₀ been found to be non-flammable when exhausted into air due to the dilution of the hydrogen content by the atmosphere.

In another embodiment of the invention, the azide and nitrate components of the propellant blends 5 are combined in approximately stoichiometric proportions as known in the art. These compositions

SUBSTITUTESHEET are, however, modified by the addition of a mixture of an inert silicon-containing compound, such as silicon dioxide, and a metal oxide whose metal component has a melting point such that the metal remains substantially solid at the deflagration temperature of the propellant. The amount of these two materials is specifically chosen to substantially prevent the formation of particulate combustion products in the propellant gas. This occurs by forming a solid slag or clinker which remains within the gas generator and thus captures the particulates so as to prevent them from entering the ballast tanks. Use of such blends of the type described above, chosen to form the solid clinker and thus prevent the escape of particulates from the generator, provides a substantially improved performance over other materials relied upon for this purpose in the prior art.

Detailed Description of the Invention

The present invention is directed to solid propellant compositions for use in emergency deballasting systems for submersible vessels. These compositions comprise, in a first embodiment, non- stoichiometric blends of an alkali metal azide and an alkali metal nitrate. Of the alkali metals listed in Group IA of the Periodic Table, sodium and potassium are presently contemplated for use in the invention on the basis of their cost, availability and relatively low atomic weight, i.e., compared to that of rubidium, cesium and franciu , some of the remaining alkali metals. Lithium, which has even a lower atomic weight than that of either sodium or potassium, is correspondingly even more useful in the invention. At the present time, however, lithium-based compounds are

SUBSTITUTESHEET relatively too costly to produce to render use of this material economically feasible. With the advent of new technologies for producing lithium-based compounds, such that the price of this material might be correspondingly reduced, a blend of lithium azide and lithium nitrate is clearly preferred for use in the invention.

As disclosed in the prior art, blends of alkali metal azides and alkali metal nitrates - in stoichiometric ratios - are known for a variety of applications. What has not been previously disclosed, however, or previously practiced, is the combination of these materials in non-stoichiometric blends since, as noted above, a reduction in the amount of the oxidizing component, i.e., the alkali nitrate, results in the formation of combustion products comprising nitrogen gas and molten bits of the alkali metal chosen for use. Exhausting these particulates into a ballast tank at least partially filled with sea water thus results in the formation of hydrogen gas in addition to the nitrogen gas which is already present. The amount of hydrogen generated is limited, however, to about 13-14% by volume so as to prevent the formation of an explosive mixture when combined with air.

Although it is of course clearly imperative that the concentration of hydrogen gas be maintained below a level (i.e., about 13%-14% by volume) at which an explosion could occur when the deballasting gas is mixed with air, the presence of some hydrogen in the deballasting gas is particularly useful since the hydrogen is generated upon contact with the sea water and thus serves to reduce the amount of propellant required to deballast the vessel as shown. In the examples provided below, for example, a compound

SUBSTITUTE SHEET generating 10.7% hydrogen requires 18% less propellant than the stoichiometric compound.

Accordingly, it has been discovered that by ₅ carefully controlling the ratio of the amount of alkali metal azide to that of the alkali metal nitrate, within certain narrow limits as described below, the level of hydrogen gas thus produced by the deflagration of this material can be maintained at _₀ below about 13% by volume, i.e., an amount which is not explosive when mixed with air.

To more clearly illustrate the present invention. Tables I-III below set forth the relative amount of hydrogen gas (remainder nitrogen gas) achieved with *L5 the use of various ratios of alkali metal azides to their corresponding alkali metal nitrates. As would be well understood by one skilled in the art, however, the blends disclosed in Tables I-III are capable of numerous variations. Thus, for example, the alkali o metals used to form the azide and the nitrate need not be the same in both cases as shown in the charts but rather, they can be mixed and matched within the broad category of the Group 1A metals of the Periodic Table (e.g., sodium azide with potassium nitrate). The ₅ information in these tables is provided for the purpose of illustration only and is not intended to limit the invention to the specific compositions or ratios described.

For convenience in comparing the values obtained ₀ with the non-stoichiometric blends of the present invention to those obtained with stoichiometric mixtures of these materials, the first line of each table represents a stoichiometric mixture of the particular azide and nitrate shown. 5

SUBSTITUTESHEET TABLE I

REACTION

5NaN₃ + NaN0₃ > 3Na₂0 + 8N₂

6NaN₃ + NaN0₃ > 3Na₂0 + 9. 5N₂+Na

7NaN₃ + NaN0₃ > 3Na₂0 + HN₂+2Na

8NaN₃ + NaN0₃ > 3Na₂0 + 12.5N₂+3Na

9NaN₃ + NaN0₃ > 3Na₂0 + 14N₂+4Na

TABLE II

REACTION

5KN₃ + KN0₃ > 3K₂0 + 8N₂

6KN₃ + KN0₃ > 3K₂0 + 9 . 5N₂+K

7KN₃ + KN0₃ > 3K₂0 + 11N₂+2K

8I N₃ + KN0₃ > 3K₂0 + 12 . 5N₂+3K

9KN₃ + KN0₃ > 3K20 + 14N₂+4K

TABLE III

REACTION

5LiN₃ + LiN0₃ > 3Li₂0+8N₂

6LiN₃ + LiN0₃ > Li₂0+9. 5N₂+Li

7LiN₃ + LiN0₃ > 3Li₂0+llN₂+2Li

8LiN₃ + LiN0₃ > 3Li₂0+125N₂+3Li

9LiN₃ + LiN0₃ > 3Li₂0+14N₂+4Li

The present invention is thus intended to include propellant compositions comprised of an alkali metal azide and an alkali metal nitrate wherein the ratio of the azide to the nitrate ranges from just above stoichiometric, i.e., wherein a minimal amount of hydrogen gas is produced, to a value that will result in the formation of no more than about 12.5% by volume of hydrogen in the combustion gas since, as noted above, at exhaust gas concentrations of about 13%-14% by volume and above, hydrogen tends to form an explosive mixture when mixed with air.

SUBSTITUTE SHEET These values will necessarily vary depending upon the particular azide/nitrate combination used. For instance, with a blend of sodium azide and sodium nitrate as set forth in Table I, the amount of sodium azide utilized preferably ranges between about 79.5 and 87.3 wt. % with a sufficient amount of the nitrate present to total 100% by wt. For blends of potassium azide and potassium nitrate (Table II) , the corresponding percentage range of KN₃ from about 80.2 to 87.8 wt. %. For lithium azide and lithium nitrate (Table III) , this preferable range is about 78.2 to about 86.5 wt. %.

As may be determined for example from Table I, therefore, the composition represented by the last line, i.e., 87.3% NaN₃ and 12.7% NaN0₃, produces 22% more gas

[i.e., ((10.83)-(8.85) (8.85)) x (100) = 22.3%] than the stoichiometric mixture shown in the first line. The former composition indicates the maximum amount of sodium azide permitted for use in the present invention while still maintaining the level of hydrogen present in the deflagration product (i.e., before being mixed with air in the ballast tanks) below about 13%-14% by volume. Similar improvements in the amount of gas produced are shown in Table II (21.9%) and Table III (23.1%). .An alternate embodiment of the invention concerns propellant blends adapted to prevent both the formation of hydrogen gas in the combustion products as well as the passage of molten particulates produced during deflagration from the gas generators to the ballast tanks. The subject embodiment comprises, as described above, blends of alkali metal azides and nitrates, which in this instance are blended in approximately stoichiometric ratios. As discussed above, such blends produce a substantial amount of particulate combustion products upon deflagration. These products at least partially include small liquid particles of the alkali metal oxide(s) which comprise the

SUBSTITUTE SHEET propellant. Upon contact with sea water in the ballast tanks, caustic hydroxides such as sodium hydroxide (NaOH) , potassium hydroxide (KOH) and lithium hydroxide (LiOH) (depending upon which alkali metals are present) , are formed. These caustic solutions may cause damage to some ballast tank components over time.

In order to prevent such damage, it is known to combine stoichiometric propellant blends of, e.g., alkali azides and alkali metal oxides used in some automobile passive restraint systems with an inert silica-containing compound (e.g., silicon dioxide) to form a solid sodium silicate slag or clinker, thus trapping the molten particles. It has now been discovered, however, that by combining the silicon-containing compound with a carefully controlled amount of a metal oxide such as ferric oxide (Fe₂0₃) , a substantial improvement in the amount of particulate material retained as clinker is obtained. The use of such a metal oxide with the alkali metal azide/alkali metal nitrate blends of the present invention has not been previously known. Moreover, although ferric oxide is the preferred metal oxide for use in the invention, any metal oxide, such as the oxides of titanium, nickel, vanadium, manganese, chromium and cobalt, may be used wherein the metal component of the oxide has a sufficiently high melting point such that the compound remains substantially solid at the reaction temperature at which deflagration takes place. The preferred amount of metal oxide may vary depending upon which oxide is used but will preferably range between about 5 and 18% by weight.

For convenience in understanding this embodiment of the invention. Table IV set forth below illustrates the results obtained by using either silicon dioxide or iron oxide to form the clinker, as compared to the combination of these two materials. Moreover, although the percentage of solids is provided only for the sodium-containing salts

SUBSTITUTESHEET in Table IV, the use of lithium or potassium salts would provide comparable results. These tests were performed in small-scale gas generators containing approximately one pound of propellant. The results thus obtained are provided for purposes of illustration only, however, and are not intended to limit the invention in any manner.

As can be determined from Table IV, the use of Si0₂ alone to form the clinker results in 59.7% of the particulates being retained, whereas using only Fe₂0₃ raises this figure to 85.5 wt %. However, the use of both Si0₂ and Fe₂0₃, which is nowhere taught in the- prior art, results in 91.7% by weight of the particulates being retained, an improvement of over 7% percent. By extrapolating this improvement over the total number of a plurality of gas generators used in the deballasting operation, it can be seen that a substantial reduction in the total amount of particulates reaching the ballast tanks is obtained, thus providing a significant improvement over the materials previously utilized for this purpose. The compositions of the present invention meet or exceed all of the constraints identified by the U.S. Navy for deballasting systems of the type described herein, namely: the vessel's recovery must take place rapidly enough to limit the total amount of flood water

SUBSTITUTESHEET admitted into the hull in the event of structural failure; the deballasting gas must be: - non-explosive (when mixed with air) , non-toxic (when personnel may be exposed) , and non-corrosive to the ballast tank structure and piping; the heat introduced into the ballast tank must not cause the temperature of the pressure hull to rise more than 100°F, nor that of the ballast tank structure to rise more than 600°F; and the gas generant fuel must be - safe to handle, transport and store, non-toxic (if stored within the pressure hull) and reliable after 20 years of storage.

SUBSTITUTESHEET

Claims

CLAIMS5 I claim:

1. A solid propellant composition for deballasting submersible vessels comprising a blend of an alkali metal azide and an alkali metal nitrate wherein the ratio of the azide to the nitrate ranges from above stoichiometric to an

₁₀ amount which will result in the production of no more than about 13% by volume of hydrogen gas upon deflagration of the composition.

2. The composition of claim 1 wherein the alkali _₅ metal is selected from the group consisting of sodium, potassium and lithium.

3. The composition of claim 1 wherein the azide and the nitrate both contain the same alkali metal. 0

4. The composition of claim 3 wherein the azide is sodium azide and the nitrate is sodium nitrate.

5. The composition of claim 4 wherein the sodium 5 azide ranges between about 79.5 and 87.3% by weight and wherein the sodium nitrate ranges between about 20.5 and 12.75% by weight of the total composition.

6. The composition of claim 3 wherein the azide is ₀ potassium azide and the nitrate is potassium nitrate.

7. The composition of claim 6 wherein the potassium azide ranges between about 80.2 and 87.8% by weight and wherein the potassium nitrate ranges between about 19.8 to 5 12.2% by weight of the total composition.

SUBSTITUTE SHEET 8. The composition of claim 3 wherein the azide is lithium azide and the nitrate is lithium nitrate.

9. The composition of claim 8 wherein the lithium azide ranges between about 78.2 and 86.5% by weight and the lithium nitrate ranges between about 21.8 and 13.5% by weight of the total composition.

10• The composition of claim l wherein the azide and the nitrate each contain different alkali metals.

11. A solid propellant composition for deballasting submersible vessels comprising: a substantially stoichiometric blend of an alkali metal azide and an alkali metal nitrate capable, upon deflagration, of producing a substantial quantity of gaseous combustion products, said combustion products comprising a plurality of molten particles of said alkali metal; and at least one metal oxide capable of reacting with said molten particulate material to form a substantially solid clinker, wherein the metal of which said oxide is formed has a sufficiently high melting point to permit said metal to remain in a substantially solid state during deflagration of said composition.

12. The composition of claim 11 which further comprises an effective amount of a substantially inert silicon-containing compound to facilitate formation of said solid clinker.

13. The composition of claim 12 wherein said silicon- containing compound is silicon dioxide.

SUBSTITUTESHEET 14. The composition of claim 11 wherein said metal oxide is selected from the group consisting of oxides of iron, titanium, nickel, vanadium, manganese, chromium and cobalt.

15. The composition of claim 11 wherein said metal oxide is present in an amount of between about 5-18% by weight of said composition.

16. The composition of claim 11 wherein the azide and the nitrate are both contain the same alkali metal.

17. The composition of claim 16 wherein the azide is sodium azide and the nitrate is sodium nitrate.

18. The composition of claim 16 wherein the azide is potassium azide and the nitrate is potassium nitrate.

19- ^τ*he composition of claim 16 wherein the azide is lithium azide and the nitrate is lithium nitrate.

20. The composition of claim 11 wherein the azide and the nitrate each contain different alkali metals.

21. A solid propellant composition for deballasting submersible vessels comprising: a substantially stoichiometric blend of an alkali metal azide and an alkali metal nitrate capable, upon deflagration, of producing a substantial quantity of gaseous combustion products, said combustion products comprising a plurality of molten particles of said alkali metal; at least one metal oxide capable of reacting with said molten particulate material to form a substantially solid clinker; and

SUBSTITUTESHEET an effective amount of a substantially inert silicon-containing compound to facilitate formation of said solid clinker, wherein the metal of which said oxide is formed has a sufficiently high melting point to permit said metal oxide to remain in a substantially solid state during deflagration of said composition.

SUBSTITUTESHEET [received by the International Bureau on 14 August 1992 (14.08.92); original claims 11-21 replaced by amended claims 11-19; other claims unchanged (2 pages)]

8. The composition of claim 3 wherein the azide is lithium azide and the nitrate is lithium nitrate.

₅ 9. The composition of claim 8 wherein the lithium azide ranges between about 78.2 and 86.5% by weight and the lithium nitrate ranges between about 21.8 and 13.5% by weight of the total composition.

₁₀ 10. The composition of claim 1 wherein the azide and the nitrate each contain different alkali metals.

11. A solid propellant composition for deballasting submersible vessels consisting 15 essentially of: a substantially stoichiometric blend of an alkali metal azide and an alkali metal nitrate capable, upon deflagration, of producing a substantial quantity of gaseous combustion products, said 2₀ combustion products comprising a plurality of molten particles of said alkali metal; at least one metal oxide capable of reacting with said molten particulate material to form a substantially solid clinker; and ₂5 an effective amount of a substantially inert silicon-containing compound to facilitate formation of said solid clinker, wherein the metal of which said oxide is formed has a sufficiently high melting point to permit ₃₀ said metal oxide to remain in a substantially solid state during deflagration of said composition.

12. The composition of claim 11 wherein said silicon-containing compound is silicon dioxide.

35

13. The composition of claim 11 wherein said metal oxide is selected from the group consisting of oxides of iron, titanium, nickel, vanadium, manganese, chromium and cobalt.

14. The composition of claim 11 wherein said metal oxide is present in an amount of between about 5-18% by weight of said composition.

15. The composition of claim 11 wherein the azide and the nitrate both contain the same alkali metal.

16. The composition of claim 15 wherein the azide is sodium azide and the nitrate is sodium nitrate.

17. The composition of claim 15 wherein the azide is potassium azide and the nitrate is potassium nitrate.

18. The composition of claim 15 wherein the azide is lithium azide and the nitrate is lithium nitrate.

19. The composition of claim 11 wherein the azide and the nitrate each contain different alkali metals.