US2710793A - Solid gas generating units - Google Patents

Description

some GAS GENERATING UNITS Alexander Cantlay Hutcllison, Saltcoats, Scotland, assignor to Imperial Chemical Industries Limited, a corporation of Great Britain No Drawing. Application April 8, H54, Serial No. 421,981

4 Claims. (Cl. 52-0.5)

The present invention is concerned with improvements in solid gas generating units comprising solid gas generating charges of the kind capable of propagating through themselves a self-sustained, exothermic, non-detonating, gas-evolving decomposition when a merely local portion of the charge is heated from room temperature to the temperature at which its active decomposition begins or which in combination with one or more components of said units are capable of decomposing in said manner. Solid gas generating charges of the kind capable of propagating through themselves a self-sustained, exothermic, non-detonating, gas-evolving decomposition in the aforesaid manner have found application for a variety of purposes including, for instance, the actuation of gas pressure operated mechanical devices, blasting operations, the

dispersion of volatilisable pesticides, insect repellents,

rodenticides, propulsion of rockets, the expulsion of liquids from containers such as fire extinguishers and the driving of turbines.

This application is a continuation-in-part of my application, Serial No. 123,981 filed October 27, 1949.

It is known that guanidine nitrate undergoes an exothcrmic gas evolving decomposition but only when it is strongly heated. Under atmospheric pressure conditions the reaction does not sustain itself if a portion only of a quantity or" the compound is heated from atmospheric temperature to the temperature at which decomposition begins, unless external heating is maintained. The decomposition leads to the production of gases containing steam, nitrogen, ammonia and oxides of carbon, but there is also formed a certain amount of a difiicultly fusible yellow nitrogenous organic residue.

Conversely, when the conditions are such that the prevailing gas pressure is sufiiciently high, namely of the order of 70 atmospheres, once the reaction has been locally initiated it will sustain itself throughout a mass of the guanidine nitrate.

Attempts have been made to provide charges capable of decomposing with a high yield of permanent gases when locally heated by a non-detonating element, at a lower pressure than guanidine nitrate, said mixtures com prising guanidine nitrate with a proportion of a metallic hypophosphite or ammonium hypophosphite whereby, if desired, charges capable of supporting their decompositions even at atmospheric pressure when locally heated may be obtained. I

However, owing to the nature or amount of the residue the hypophosphites leave behind or other disadvantages attendant on their employment these charges have only a limited applicability and it would be desirable to provide improved gas generating charges based on guanidine nitrate and/or nitroguanidine, and capable of self-sustained decomposition under conditions of much lower gas pressure than guanidine nitrate alone.

it is also known that the pressure required to render possible the self-sustained decomposition of a charge based on guanidine nitrate may be progressively reduced by making up the guanidine nitrate into charges with progres- "nited States atent ice sively increasing amounts of colloided nitrocellulose as a binding agent, by mixing the guanidine nitrate with a solution of nitrocellulose in a volatile solvent, forming the resulting paste into the required shape and evaporating oil the volatile solvent, but the use of a volatile solvent adds to the expense and necessitates a drying operation, while the applicability of this method is also somewhat limited.

Prior art in the field show gas producing charges comprising nitroguanidine and/or guanidine nitrate and a pulverulent metal, non-metal, or metallic compound sensitiser, other than a metallic hypophosphite or ammonium hypophosphite, for the thermal decomposition of nitroguanidine and/ or guanidine nitrate.

Further, such art shows that gas-generating charges suitable for a variety of purposes, free from disadvanrages attendant on the use of hypophosphite or gelatinised nitrocellulose and capable of self-sustained nondetonating decomposition when merely locally heated, providing a high yield of hot gases and maintaining propagation of the reaction under considerably lower gas pressures than are required for guanidine nitrate, may be obtained by the use in admixture with guanidine nitrate of a polynitro-phenol or a polynitroso-phenol. Gas generating charges are disclosed comprising guanidine nitrate in admixture with a polynitro-phenol or a polynitroso-phenol. These charges may include if desired an aliphatic carboxylic acid selected from the group consisting of tartaric, maleic, citric and fumaric acids with or without the inclusion of a small proportion of vanadium pentoxide which if desired may be in the form of a chemically equivalent vanadium compound. These charges may also include a small percentage of a heat resisting material having a large surface area and amounting to not less than 0.25% of the weight of the charge.

The principal object of the present invention is to provide gas generating units adapted to generate hot gases at temperatures higher than 600 C., said gas generating units comprising nitroguanidine and/or guanidine nitrate, at least one non-explosive inorganic reagent which in sufficient amount is able to eiiect a self-sustained thermal decomposition of nitroguanidine and/ or guanidine nitrate when locally heated and a heat-resisting material having a large surface area.

Another object of this invention is to provide gas generating units as noted heretofore wherein said inorganic reagent is selected from the group consisting of molybdic acid, ceric oxide, and vandaium pentoxide and said heat resisting material is asbestos fibre.

A further object of this invention is to provide gas generating units as noted heretofore wherein said nitrogen containing compound is in amount of from about 89% to 98.8% by weight of the total unit, said inorganic reagent is in amount of from about 0.2% to 10% by weight of the total unit, i. e., the ratio by weight of the nitrogen containing compound to the inorganic reagent is between the values of 98.8 to 0.2 and 89 to 10, and the heat resisting material is in amount of from about 0.25% to 1% by weight of the total unit.

The heat resisting material having a large surface area is always maintained in immediate proximity to an exposed surface of nitroguanidine and/or guanidine nitrate composition undergoing thermal decomposition at said surface. Thus, the condensable vapourisable organic compounds that are formed are caused to pass, before cooling takes place, over or through said heat resisting material thereby causing a further exothermic reaction and so further increasing the temperature and the yield of hot gases. The heat resisting material may either be external to the nitroguanidine and/or guanidine nitrate composition, or may be actually included in the composition. If the heat resisting material is external to the composition, then, of course, any amount thereof can be used governed only by economy and convenience. However, if the heat resisting material is actually included in the composition, then an amount of from about 0.25% to 1% by weight of the total unit is contemplated. A preferred range for the heat resisting material wien included in the composition is from about 0.25% to 0.5% by weight of the total unit.

Examples of the said non-explosive inorganic reagents which in sufficient amount either alone or in conjunction one with another are able to effect the self-sustained thermal decomposition of nitroguanidine and/or guanidine nitrate when locally heated are molybdic acid, eerie oxide, and vanadium pentoxide. As noted heretofore, such non-explosive inorganic reagent must be in amount of from about 0.2% to 10% by weight of the total unit. A preferred range for the inorganic reagent is from about 0.2% to 6% by weight of the total unit.

The said non-explosive inorganic reagents need not be incorporated in the nitroguanidine and/or guanidine nitrate but may be included in the said heat resisting material which although maintained in immediate proximity to the one or more surfaces of the nitroguanidine and/or guanidine nitrate which are to undergo selfsu'stained thermal decomposition is nevertheless wholly external to such surface or surfaces.

The non-explosive inorganic reagent utilized in this invention is such that, in the absence of said heat resisting material having a large surface area, it is unable to bring about the desired complete self-sustained thermal decomposition.

As noted heretofore, the nitrogen containing compound can be in amount of 89% to 98.8% by weight of the total unit.

Gas generating units made in accordance with the invention may be used, for instance, for actuating gas pressure operated mechanical devices, e. g. for driving engines and turbines, or for operating pneumatic tools, for operating fire extinguishers, for propulsion of rockets or other gas escape reaction propelled devices, e. g. jet

propelled toys and models, for inflation of buoyant apparatus, clearing obstructed pipes, for making colored smokes or for safety blasting operations by means of blasting assemblies in which the charge of the gas generating unit is caused to undergo decomposition in a pressure resisting container adapted to vent the gas once a predetermined pressure has been built up within the container.

It will be understood that according to the purpose for which the gas generating unit is required the charge of said unit may be in powder, granular or compact form of any required shape.

The preferred ranges noted heretofore for the basic ingredients of the gas generating unit are illustrated by the following examples in which the parts are parts by weight.

EXAMPLE 1 A mixture consisting of the following ingredients:

Parts Guanidine nitrate 94.7

Molybdic acid 5.0 Asbestos fibre 0.3

is prepared by grinding the ingredients in a pestle and mortar until an intimate mixture is obtained. 45 gms. of the mixture is then loaded into a 1" diameter cartridge tube rolled from absestos paper and is consolidated by pressing, the cartridge being supported for the time being by a steel mould. The pressed cartridge is placed in a steel vessel of 100 cu. ins. capacity, the vessel closed and the charge ignited electrically. The charge decomposes in a self-sustained manner giving oif a steady stream of gas over a period of 2%. minutes thereby raising the pressure in the vessel to 260 lbs./ sq. in. The hot broad aspect.

gases are evolved at a temperature of between 900 C. to 1000 C., but are rapidly cooled by loss of heat to the walls of the vessel. The pressure falls slightly to 230 lbs/sq. in. as temperature equilibrium is reached. This experiment shows the suitability of the composition for the slow generation of gas pressure for such uses as the expulsion of liquids from fire extinguishers or the inflation of buoyant apparatus or the like.

EXAMPLE 2 Instead of using molybdic acid as sensitising agent for guanidine nitrate as quoted in Example 1, ceric oxide is used in the following proportion:

Parts Guanidine nitrate 94.5 Ceric oxide 5.0 Asbestos fibre 0.5

The above composition may be compressed into solid charges of any desired shape and used for such requirements as are indicated in Example 1.

The temperature of the hot gases evolved is about 900 C. to 1000 C.

EXAMPLE 3 Instead of using eerie oxide, vanadium pentoxide is employed as a sensitising agent for the guanidine nitrate as in the following composition.

Parts Guanidine nitrate 98.5 Vanadium pentoxide 1.0 Asbestos fibre 0.5

The temperature of the hot gases evolved is about 900 C. to 1000 C.

EXAMPLE 4 A porous pad of asbestos fibre is arranged to be maintained in close contact with the surfaces of a compressed charge of any of the compositions mentioned in Examples l to 3 which are, however, to be free from asbestos fibre. Then if surfaces of the charge adjacent to the porous pad of asbestos fibre are heated e. g. by an incendiary mixture, to cause partial decomposition and volatilization of the guanidine nitrate mixture a gas phase reaction takes place in the asbestos fibre of said porous pad and liberates sufficient heat to decompose more guanidine nitrate mixture and so on. A self-sustained decomposition of the mixture is thereby obtained provided that the asbestos pad is kept adjacent to the reacting surface or the charge. A gas generating unit constructed in this way forms a convenient means for obtaining a selfsustained gas producing reaction having a particularly advantageous feature in that the charge of said unit may be one which reacts only on the surface adjacent to the asbestos pad. This makes it possible to obtain a controlled burning of a charge in one direction only without elaborate protection of side surfaces.

The temperature of the hot gases evolved is about 900 C. to 1000 C.

The following examples set out in tabular form are also submitted since they illustrate the invention in its These examples show use of the various ingredients in the broad ranges noted heretofore and parts are parts by weight.

The charges are constructed so that the diameter of each cartridge is 1.5 inches, so that the weight of the composition in each cartridge is 70 gms. and so that the composition is directly pressed in an asbestos lining positioned in a cylindrical steel vessel 3.5 inches deep and 1.5 inches diameter in which vessel the cartridge thus formed is fired under a pressure of the order of 400 1b./ sq. in. in an atmosphere of nitrogen.

Components:

Guanidine nitrate Components:

Nitroguanidine 98. 8 98. 8 98. 8 89 89 89 98. 5 98. 5 98. 5 Asbestos 1. 0 1. 0 1.0 1.0 1. 0 1. Q 0. 25 0. 25 0. 25 Molybdic aoid 0.2 10. 0 1. 25 Oeric oxide 0. 2 10. 0 1. 25 Vanadium pentoxi e.- 0. 2 10.0 1. 25 Length of charge (ins) 1. 82 1. 67 2.15 1. 71 1.78 1. 76 1. 79 1. 77 1. 86 Time of burning (sees 27. 0 26. 25 31. 75 17. 0 26. 0 10. 25 47. 9 22. 2 14. 5 Pressure (p. s. i.)... 500 450 400 500 43 450 500 500 460 Burning speed (ins. .068 .064 .068 106 .069 172 .037 .080 13 I claim:

1. A gas generating unit capable of propagating throughout itself a self-sustained exothermic non-detonating gas evolving decomposition comprising in association at least one nitrogen containing compound selected from the group consisting of nitroguanidine and guanidine nitrate, at least one non-explosive inorganic reagent selected from the group consisting of molybdic acid, ceric oxide, and vanadium pentoxide, and a heat resisting material consisting of asbestos fibre wherein the ratio by weight of the nitrogen containing compound to the inorganic reagent is between the values of 98.8 to 0.2 and 89 to 10.

2. A gas generating unit capable of propagating throughout itself a self-sustained exothermic non-detonating gas evolving decomposition comprising in association at least one nitrogen containing compound selected from the group consisting of nitroguanidine and guanidine nitrate in amount of from about 98.8% to 89% by Weight of the total unit, at least one non-explosive inorganic reagent selected from the group consisting of molybdic acid, ceric oxide, and vanadium pentoxide in amount of from about 0.2% to 10% by weight of the total unit, and a heat resisting material consisting of asbestos fibre wherein said heat resisting material is in admixture with the nitrogen containing compound and the non-explosive inorganic reagent and is in amount of from about 0.25% to 1% by weight of the total unit.

3. A gas generating unit as claimed in claim 1 wherein said heat resisting material is maintained in the immediate proximity of at least one exposed surface of the composition comprising said nitrogen containing compound.

4. A gas generating unit as claimed in claim 1 wherein said nitrogen containing compound is guanidine nitrate.

No references cited.

Claims (1)

1. A GAS GENERATING UNIT CAPABLE OF PROPAGATING THROUGHOUT ITSELF A SELF-SUBSTAINED EXOTHERMIC NON-DECONATING GAS EVOLVING DECOMPOSITION COMPRISING IN ASSOCIATION AT LEAST ONE NITROGEN CONTAINING COMPOUND SELECTED FROM THE GROUP CONSISTING OF NITROGUANIDINE AND GUANIDINE NITRATE, AT LEAST ONE NON-EXPLOSIVE INORGANIC REAGENT SELECTED FROM THE GROUP CONSISTING OF MOLYBDIC ACID, CERIC OXIDE, AND VANADIUM PENTOXIDE, AND A HEAT RESISTING MATERIAL CONSISTING OF ASBESTOS FIBRE WHEREIN THE RATIO BY WEIGHT OF THE NITROGEN CONTAINING COMPOUND TO THE INORGANIC REAGENT IS BETWEEN THE VALUES OF 98.8 TO 0.2 AND 89 TO 10.