US 2682461 A
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Patented June 29, 1954 STATE ATEN T" QFIEE,
SOLID "GAS GENERATING CHARGE No Drawing. Application November'18, 1949',
Serial'No. 128, 240 7 Claims priority; application GreatBritain January 12, 1949 The :present invention relates to improvements insolid gas-generating.- charges of? that kind capable of propagatingthrough. themselves a self-sustainingv exothermic: non-detonating gasevol-ving; decomposition whena'merely local portion of the charge is -heated'from' 'roomitempera ture to the temperature at which. itsfaotivel d'ecomposition begins.- Such gasl generating chargeshave found-application for: a variety of. purposes including, for instances, the. actuation of gas pressure: operated mechanical devices,- blastinggoperations; thedispersion of .volatilizablepesticides, insectrepellants; rodenticides; propulsion of1rockets-and the-expulsion of liquids fromcontainers such asvfire extinguishers.
It is known-that guanidine nitrate" undergoes an exothermic gas-evolvingdecomposition when it is strongly heated, butunder-atmospheric pressure conditionsthe reaction -does not'sustain it-- self: if a portion -only-' of. a quant-ity of :thet-com M pound. is heated from atmospherictemperature to the temperature at which :decomposition b'e-- gins,'unless external heatingismaintained. The decomposition leads to the production ofxgases which include. steam; nitrogen,- ammonia: and oxides of carbon, but'there is also formed accr tain amountof a di-fiicultl-y fusible-yellow nitrog-ienousorganic residue.
When i the conditions-- are such thatthe pre vailinggas pressure is sufi-iciently high, namely ofzthe order of 70 atmospheres,- oncewtheruaction has .been locally initiated -itwill sustain itself throughout a mass .of the guanidineznitrater It has been proposed toprovide charges-capable of. decomposing I. in a self-sustained:manner."with a high yieldof permanent gases-when -locallyh'eatedby. anon -detonating element, atra lower pressure than guanidine. nitrate;v said mixtures comprising guanidinecnitratelwith aproportion of a metallic hypophosphitecor ammonium hy- DOphosphite whereby, if desired; charges capable of. supporting their decomposition evenat U atmospheric pressurawhen locally. heated may. be obtained;
Owing to the .nature or amounton the residue the hypophosphites leave behind or otherldisadvantages attendant on their employment, these charges have a limited applicability and it would be desirable" to prov-ide improved-gas-gencrating charges based on guanidine nitrate and capable of self-sustained decomposition under" conditions ofmuch-lowergas-pressure-than guanidine nitrate .alone.
It is also known that the-pressure required Ito render. possible .the self-sustained decomposition progressively reduced by. making up theaguanidine nitrate into charges with progressively increasing amountsof colloided' nitrocellulose asa binding agent, by; mixing the-guanidine nitrate 5 with a solution of nitrocellulose in a volatile sol vent, forming the resulting paste into the required shape and evaporating oiT the volatile solvent, but the use ofa volatile solvent adds to the expense and necessitates adryingoperatiomwhile the applicability of this method is also some- What limited.
In British patent specification No." 627,724:
phite, for the thermal decomposition ofnitro-- guanidine and/or guanidine nitrate.-
it is stated that it has been found that-gas-generating charges suitable for a variety of purposes free from. disadvantages: attendant on the use of hypophosphiteor gelatinisednitrocellulose and capable of self-sustained non-detonating decomposition when merely locally heated, with a high yield of hot gases underconsiderably lower gas pressures than are required for guanidine nitrate, may be obtained' bythe use-in admixture with guanidine-nitrate of apolynitrophenol or a polynitrosophenol. Thus co pending- British specification No. 644,073 claims inter alia gasgenerating charges comprising guanidine nitrate in admixture with a polynitrophenolor a polynltrosophenol.
equivalent vanadium: compound. These charges may alsoinclude a small percentage ofa heat resisting material having a large surface area and amounting to not lessthan-0-.25% of the weight of the charge. Furthermore these-charges"- may include thermally volatilizable materials; as
for example, insect repellants, insecticides, fungicides, bactericides; and other pesticides.
The object ofthe'present'invention is to pro vide solid gas-generating charges of the kind capable of propagating through themselves a selfsustaining exothermic non-detonating gas-evolving decomposition of guanidine nitrate in adm-ixture with at least "one solid 'polyhyd-roxy organic compound. having a ratio of hydroxylof .a charge basedpn-guanidinenitrate maybe 5' groups-to carbon atoms-.of'at least 1 to1'2 :in the In cO-pending British specification No. 644,073-- I These charges may includeif desired an aliphatic oarboxylicacid selected fromthegroup consisting of tartaric, maleic, citric and fumaric acids with or-without the inclusion :ofa small proportion of vanadium pentoxide' which if desiredmay be in the formof a chemically molecule and which is incapable of supporting its combustion in the absence of oxygen.
According to the present invention gas-generating charges comprise guanidine nitrate in intimate admixture with at least one solid organic polyhydroxy compound having a ratio of hydroxyl groups to carbon atoms in the molecule of at least 1 to 2 and which is incapable of supporting its combustion in the absence of oxygen.
In the absence of diluents or heat-absorbing ingredients a proportion of the said organic compounds amounting to about 5 to 25 per cent of the weight of the guanidine nitrate sufiices to render the composition capable of self-sustained decomposition when locally heated, under atmospheric pressure conditions or under conditions of slightly elevated pressure.
t is an advantage of the invention that the compositions may be made by simple admixture of the ingredients, and that when the charge is required to be of compact structure and predetermined form so that it will react only on its exposed external surface it may be made by compressing the mixture into a mould of the desired shape. Moreover, if it is required to protect a portion of the surface of the compact charge from the hot gases evolved by means of an adherent coverin of heat-insulating material, this may if desired be done in the course of the pressing operation instead of applying protective material to the surface of the charge after it has been shaped.
When charges made up from guanidine nitrate and a solid organic compound of the aforesaid kind are consumed under atmospheric pressure conditions or at comparatively low super-atmospheric working pressures for example up to about atmospheres, their decomposition into gaseous products is not quite complete, and they leave a certain amount (usually to of the difficultly fusible nitrogenous organic residue already referred to.
We have found however that the inclusion of a proportion of vanadium pentoxide in a quantity insufficient in the absence of said solid organic polyhydroxy compound to support the self-sustained thermal decomposition at atmospheric pressure of said gas-generating charges, amount ing for example to about 0.2 to 1 per cent of the weight of the guanidine nitrate, has the effect in most cases of completing the decomposition of the guanidine nitrate thus obviating the formation of the aforesaid yellow difficultly fusible organic residue and correspondingly increasing the yield of hot gases at working pressures at which this residue would otherwise be formed; and we preferably include in the charge such a proportion of vanadium pentoxide or the equivalent proportion of a chemically equivalent vanadium compound e. g. ammonium vanadate.
It has also been found that a compound of molybdenum e. g. molybdic acid may be used in place of a vanadium compound.
At comparatively low super-atmospheric pressure and under the above conditions the gases contain appreciable quantities of vaporized con- 0 densable organic materials, the presence of which may be undesirable in certain applications of the charges, e. g. if they are to be used in driving engines or operating other mechanical devices where these organic vapours can condense and cause fouling of pipes or moving parts.
We have further found that the condensable vaporized organic compounds that would otherwise be formed at pressures near atmospheric may be destroyed as a result of an exothermic reaction further increasing the hot gas yield, by causing the mixture of gases and vapours, before cooling takes place, to pass over or through suitable heat resisting catalytic solid surfaces such as asbestos or fine wire gauze of iron, steel or platinum, or including in the composition of the charge a small percentage of asbestos fibre or other heat resisting material characterised by a large surface and amounting to not less than about 0.25% of the weight of the charge. The large surface material also steadies the self-supporting characteristics of the reaction and holds together the ash of the charge. It may be desirable to include a small percentage of potassium nitrate in the charge, amounting, for instance, to about0.25% to 1%, since the potassium nitrate assists the reaction between the gases and vapours on the solid catalytic surface.
Charges made in accordance with the invention may be used for instance for actuating gas pressure operated mechanical devices e. g. for driving engines, or for operating pneumatic tools, for operating fire extinguishers, for propulsion of rockets and other gas escape reaction propelled devices, for dispersing insecticidal or the like substances, for making coloured smokes, or for safety blasting operations by means of blasting assemblies in which the charge 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 charge is required it may be in powder, granular or compact form of any required shape and may or may not include ingredients for reducing or raising the temperature of the gases it generates. The hereinafter mentioned thermally volatilizable materials are examples of ingredients which reduce the temperature of the said gases and by way of example ammonium perchlorate and ammonium nitrate are reagents which raise the temperature of the said gases.
Charges in accordance with the invention may include thermally volatilizable materials, which may be for instance, insect repellents; insecticides, fungicides, bactericides and other pesticides; smoke producing compounds or coloured dyestuffs. In this case the charge will usually be required to decompose under atmospheric pressure conditions; and if the material is an organic compound it will be understood that if the charge is to include asbestos fibre or other material of large surface characteristics its composition must be such that the gases and vapours will not undergo to any extent a reaction on its surface that would destroy the volatilizable compound in the gas stream. The volatilization of the organic compound has a cooling action so that if suflicient of this composition is used the temperature will be too low for any such undesired surface reaction to take place.
The invention is further illustrated by the following examples in which the parts are parts by weight.
Example I A mixture of the following composition:
Parts G'uanidine nitrate Tartaric acids 20 is mixed by milling in a steel ball mill until an intimate and homogeneous powder is obtained. 5 lbs. are then loaded in 3 increments into a 4.7" diameter steel tube closed at one end and lined with compressed asbestos sheeting, each increment being pressed, under a load of 5,500 lbs/sq. in. A small quantity of incendiary material is placed on top of the charge and the tube is then closed by a screw-on cap in the centre of which is a nozzle 0.128 in diameter. On igniting the incendiary material by an electrical system, self-sustaining decomposition of the charge is induced and continued for 95 secs. maintaining a mean gas pressure in the tube of 300 lbs/sq. in. In this way the charge provides a useful supply of hot gas under pressure suitable for the operation of mechanical devices. A small amount (less than 1 oz.) of a dark brown carbonaceous slag is left in the charge tube afte the test.
Example II Glucose and sucrose can each make guanidine nitrate capable of self-sustained decomposition. An intimate mixture is prepared from the powdered ingredients guanidine nitrate and glucose or sucrose in the proportions 90 parts of guanidine nitrate and parts of glucose or sucrose. The mixture is pressed into pellets about 2 cm. diameter and 1% cm. long. One surface of a pellet is then ignited by means of a flame. The pellet decomposes smoothly in a self-sustained manner giving off copious volumes of gas without showing flame or incandescence. yellow infusible residue is left behind.
1. Gas generating charges capable, upon local some 2,470,082
ignition, of self-sustaining exothermic nondetonating gas evolving decomposition comprising a preponderating amount of guanidine nitrate in intimate admixture with at least one solid organic polyhydroxy compound selected from the group consisting of tartaric acid, glucose and sucrose.
2. Gas generating charges as claimed in claim 1 wherein the proportion of the said organic compounds amounts to 5 to 25% of the weight of the guanidine nitrate in the absence of diluents and heat absorbing ingredients.
3. Gas generating charges capable, upon local ignition, of self-sustaining exothermic nondetonating gas, evolving decomposition comprising a preponderating amount of guanidine nitrate in intimate admixture with tartaric acid wherein a portion of the surface of the compact charge is protected by an adherent covering of heat insulating material.
4. Gas generating charges as claimed in claim 3 wherein the heat insulating material is asbestos fibre.
References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,165,263 Holm July 11, 1939 Tyre May 10, 1949