April 25, 1961 v M_ H, BOYER 2,981,616 GAS GENERATOR GRAIN Filed ÜCÍ'. l, 1956

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BY M2M AGENT 'lf `tent _ ICC 2,981,616 UnitedI tates ï le'ensserr~ia5» 2 vand x represents the valency 'of M, and (2)V at least Forio oxidizing compound selected from the Aclass consistirfg of metal peroxides, inorganic perchlorates and metal iii 2,981,616 trates; said azides and said oxidizing ‘compounds bein‘g GAs GENERATOR GRAIN present in amounts expressed by the V’equation rdm-'45', wherein n represents the number of azide atoms, Myron H. Boyer, Puente, Calif., assignor to m represents the number of equivalents ofoxidizing 'coni North American Aviation, Inc. pounds, and y lhas a numerical value of from about Y2:3 a Filed oct. 1, 1956, ser. No. 613,327 to about 3.6. ` » Y d ` ï 10 An example'of the gas generator grain of this 'inven s Claims. (el. sz­­.5) tion vis a composition comprising ’calcium'azide and pól tassium perchlorate ­in amounts ­such that 'ther-'equatiòh n/m has the value 3,. , ' ' Y " i j The azides, M(N3)x, that can be _used in the >preptufaf This invention relates to a novel composition or" matter 15 tion of ’the compositions of vthis inventionca'n Abe any suitable for generating gases. More particularly, this _azide which has suitable stability to permit grindin'grand invention relates to a composition which upon ignition Vhandling in the preparation of the composition, and alsno generates an inert gas useful for pressurizing rocket pro will burn at a satisfactory ­rate Without exploding. - 'A ¿pellant tanks. v ` class of metal azides which satisfy these 'requirements In a rocket or missile which is operated on liquid fuel, 20 are the alkali and alkaline learth azides.V Nonlimit‘i'n'g itis necessary to provide a means for supplying the fuel examples of these include , , tothe engine at a predetermined rate. This rate must , azide, and cesium azide which be of a magnitude vsuiiicient to sustain uninterrupted constitute the alkali metal azides having the general-for „combustion from which power is derived to operate the mula M(N3). Since the valence, 'xfof M, the `alkali ­rocket. ' The use of pumps is one method for supplying 25 metal is unity, thesymbol x is omitted vfrom the formula. the fuel to the rocket engine. To obviate the use of The alkaline, earth ‘azides include `the calcium aiide, »weighty pumping equipment, a method ofvfeeding the strontium azide, and .> A,The metal vM'in 'the fuel to the combustion chamber by the development of formula M(N3)X~in this case is >divalent and, "therefore, gas pressure in the fuel tank has been employed. The the symbol x has a numerical value of 2. VThe alkaline .gas Vdeveloping the pressure may be obtained from the 30 earth metals of which the azides are composed :have combustion product of a composition of matter called a atomic weights varying vfrom 40 to 138ginclus'ive. 'When gas generator grain. The gas generator grain is ignited a azide and 'are used, itlis at theftime the motor is put into operation and as com advisable to employ anexplosioninhibitor such >as `di bustiòn consumes the grain, the resulting gaseous prod atomaceous earth in order to ­reduce the 'hazard 'of vspdn‘ yl'lct‘sfe'x’e'rt a pressure inside the fuel compartment causing 35 taneous-decomposition. f. , i . ’ Í Y, Èthe fuel to ñow through feed lines to the rocket motor. _The alkali metal azides are found to be particularly ÍOfnfe. gas generator grain employed in the past _was lcorri suited to the preparation of gas generator 'grains and coní 'posedof amixture of ammonium ­perchlorate and a hydro positions containing them constitute `a preferred embodi 'carbo'n and sulfurl'co'ntainin'g polymer. Among the _com ment of this invention. The `alkali metals of which the bústion products of the gas generatorg rain were, there 40 alkali metal azides are composed have atomic weights of fore, hydrogen, carbon monoxide and hydrocarbon gases. from 6 to 133 inclusive. These are reducing _gases,land, consequently, cannot be The oxidizing compounds of which the composition >of Ítisedl `with certain types of lpropellants such as, forex matter of this invention are prepared includemetal per-oit“ ample, nitric acid, as they would destroy the oxidizing ides,V inorganic ,perchlorates y and vmetal nitrates. Vï'fI‘he •‘clutracteristic lof ­the yfuel prior to its introduction into 45 metal peroxides have thek general formula jXÍO,g wherein :the ycombustion chamber >of the motor. Also, the gases t X is a metal having. an atomic weight of from“ 6 t0 about may form vapor mixtures vwith fuels and/or ,138 inclusive, ris the number of metal atoms in the perox-l oxidizer. Other combustion products of „the sulfur-com ide compound and varies from l to_2_. . The valueof s vat'ì taining polymers are 'oxides òffsulfur. These are very ies from l to Zand representsl thenumberv of oxygen atoms 'corrosive and cause damage 'to the motor. This not only 50 in the peroxide molecule. `,Nonlirniting examplesof -met'al reduces the period of serviceability but also impairs the ­peroxides employed in the manufacture »of the composi operation of the motor Vdur-ing ñight. The result is that vtion's of this vinvention include peroxides of group-LA the missile or rocket is more diiiicult to control and metals such assodium peroxide, NazOz, potassium per increases the hazard of loss due to motor failure. A oxide, K2O2, rubidiurn peroxide, RbzOg, and cesium per need, therefore, existed for the development of a gas 55 oxide, Cs202; peroxides of group IIa-A_metals sueltas generator grain which, upon combustion, would give olf calcium peroxide, Ca'OZ; strontium peroxide,` YSrO2; barium inert gases only sowas to`•aiîect lneither the properties of the rocket fuel nor the operability of the motor. havingperoxide, >the BaOà.m general Examples formula ofY(C1`O4)„ the,inorganic,perchlor­ wherein Y fisse -It is therefore an object of this invention to provide lected from the class consisting of a metal and tlië ía composition of matter suitable for` use as a gas gen 60 ammonium radical, v represents the valenceïof. Y andv erator grain. It is also Van object of this invention to has a numerical value „of 1 ,to 3 __inclusive,pinclude àrn~ -provide a composition of matter which, upon combustion, . monium perchlorate;_group I-A metal perchloratesvpuc'h -produces only inert gaseous products. Another'object as lithium perchlorate, L_iQlO4, , sodium `>perch_loratfç'a >ofthis invention is to‘provide a method for pressurizing NaClO4, potassium perchlorate, „KClOg and`Vr 'rubidiurn propellant or fuel chambers of rockets and missiles. Other 65 perchlorate, RbClO4; group II-,A metal perchlorates such objects will become apparent from -the' discussion that as magnesium perchlorate,4 Mgt’ClOÀQZ, calciumperchlo'f «follows ’ - „ rate, Ca(ClO4)2, strontiumperchlorate,> Sr(ClO4)2, and The above and other'objects of this invention are ac barium perchlorate, Ba(KClO4)2; group VIIIv perchlorates complished by a composition of matter comprising (1) such as ferrie pt'erchlorate,­ _Fe(ClO4)3,vand cobalt ,peri „an‘azide having the general formula M(N3)¿ wherein 70 chlorate, CO( C104) 2;.and group IKII-A metal perchlora is selected ¿from the vclass rconsisting of a metal, a hy such as I`r1(ClO4)3;Y Non-limiting examples of metal nr-z vrlrazino radical Yand an >ärnmc'ouium radical; AN is nitrogen; trates having the' genera-t fórmula T(NO¿); wherein-T ' _is a `metal and z is the" valence of T having a numerical the equation nlm=y wherein n represents the number yalue of from l to 4 inclusive, include group I-A metal of azide nitrogen atoms, m represents the number of nitrates such as lithium nitrate, LiNO3, sodium nitrate, equivalents of oxidizing compounds, and y has a nu NaNO3, and potassium nitrate KNOS; group I-B metal merical value of from about 2.3 to about 3.6. ,nitrates such( as copperV nitrate, Cu(NO3)2; `and silver In addition, the compositions of this invention may ­nitrate, ~Ag(NO3); group II-A` metal‘nitrates `such as also contain minor amounts of metal and metalloid pow „magnesium nitrate, Mg(NO3)2, and‘ barium nitrate, ders and their oxides as burning catalysts. Powdered ;Ba,(NO3)2; group II-B metal nitrates such as zinc nitrate; or comminuted carbon, phosphorus and sulfur` also serve „group III-A metal nitrates such as aluminum nitrate, as burning catalysts. The amounts can range from less „AI(NO3)3, and thalium nitrate, Tl(NO3); group IV-A l0 than 0.1 weight percent to about 3 weight percent based metal nitrates such as stannic nitrate, Sn(NO3)4; group on the weight of the combined azide `and oxidizing com 'VU-A metal nitrate such as bismuth nitrate, Bi(NO3)3; pound. The particle size of the burning catalyst can group VII-B metal nitrates such as manganese nitrate, vary from about 10 to 100 microns.` Nonlimiting ex Mn(NO3)3; and` group VIII metal nitrates such as ferric amples of metal and metalloid powders and their oxides .nitrate, ferrous nitrate and nickel nitrate. Methods for that can be used as burning catalysts are copper, mag ,the preparation of metal peroxides, metal nitrates yand nesium, boron, aluminum, zirconium, vanadium, anti inorganic perchlorates are given infvolumes I and II of mony, manganese, iron, cobalt, nickel, ferrie oxide, silica, ,the text “Chemical Elements andTheir Compounds” by etc. ~ -N>°` V. Sidgwick; 1950 edition, published by the Clarendon In the preparation of the compositions of this inven Press. " ` ` . tion the metal azide and the oxidizing compound are each The metall perchlorates andthe metal peroxides are comminuted separately to a particle size ranging from „found to be particularly suited for preparing gas generator 10 to about 250fmicrons. The comminuting is per "grains having good combustion characteristics. There formed in a suitable apparatus such as a ball mill. When .­fore, compositions of this invention containing metal per working with amounts on a small scale, the comminuting ,chlorates and metal peroxides constitute a preferred em 25 may be performed by grinding with the aid of a mortar bodiment of this invention. Compositions of this inven and pestle. Precautions should‘be taken when working -ition containing metal perchlorates as the oxidizing com with compounds such as hydrazine azide that‘the de ìpounds are especially preferred because the perchlorates composition temperature is not reached. The ñnely di `have very good stability against decomposition. vided metal azide and oxidizing compound are then The ratio of the proportions of azides and oxidizing 30 blended to form a homogeneous composition. This com ¿compounds inthe composition of this invention are ex position is then made up in a suitable package for use .pressed by the equation n/m==y, wherein n represents in a missile or rocket fuel chamber for pressurization -th`e number of azide nitrogen atoms and m reuresentsthe purposes. ‘number of equivalents of oxidizing compounds. The One Vtype of gas generator grain unit is illustrated in `symbol “y” has a numerical value of from about 2.3 to Pig. l. Unit 9k consists of va cylindrical metal con ‘about 3.6. The number of equivalents of oxidizing com tainer 22 packed with an azide-oxidizer composition 25. pound is obtained by multiplying the number of molecules On top of the composition isplaced a small amount of «of oxidizing compound by the change in valence that ignition compound 26. A closure cap 23, having a the oxidizing Vcompound undergoes in its reaction with frangible disk 12 and an electrical heating element 27, the metal azides. When the oxidizing compound used 40 is'screwed into the upper end of the cylindrical metal -is a peroxide, the change in valence is‘2. This is illus container 22. By passing a current through the heat trated by the following equations: ing element 27. the ignition compound is ignited which, in turn, ignites the azide-oxîdizer composition. The pressure generated inside the container breaks the fran 45 gible disk l2 which is constructed to rupture at a pre In Equation 1 for example the valence` of sodium in determined pressure. This unit may be placed in a suit NaaOz is two, While in the product Na20 its valence is able position inside the fuel container of a rocket aircraft unity. Hence` in the reaction in which Na202 is trans so that upon ignition and combustion, the gases which formed into NaZO, the change in valence per molecule are given off will pressurize the interior of the fuel con is two. When the oxidizing molecule is a metal perchlo 50 tainer and thus act to force the fuel through feed lines rate, the change in valence per oxidizing molecule varies to the rocket motor. from 8 to 24 as determined by the number of chlorine The compositions of this invention, as well as methods atoms per molecule. the difference in the valence state for their preparation, will be more fully explained in the of each chlorine atom before and after reaction with the following examples. ëizides is 8. This is illustrated by the following equa 55 : EXAMPLE I ‘ `KClO4+8NaN3­>KCl+4Na2O+12N2 (3) Sodium azide and sodium peroxide were finely ground In(ClO4)3-{­l2Ba(N3)2­->InCl3+12BaO+36N2 (4) -to a particle size of from l0 to about 250 microns with When a metal nitrate is the oxidizing agent, the differ a mortar and pestle. To 1.55 parts cf sodium azide was ence in valence before and after reaction with the metal 60 added l part of sodium peroxide and the two blended _azides is 3 for each nitrate nitrogen as illustrated by the to form a homogeneous composition.` This composition equations was then pressed into a stainless steel cylindrical con tainer having one end closed with the `aid of a hydraulic press. Dimensions of the container were 1/2 inch in 65 side diameter-bv 4 inches long with a wall thickness of In general, the compositions of this invention consist of Mt inch. A small amount of flash powder composed of gas generator grains comprising (l) an inorganic azide a mixture of l0 parts barium peroxide and l part alumi having the general formula M(N3)x wherein M is se num metal was placed on the surface of the pressed com lected from the class consisting of `alkali metal, alkaline position. A tightly i-itting cover equipped with a heating earth metal, the hydrazino radical and an ammonium: element was placed on the container. The container radical; N is nitrogen; and x represents the valence of cover was equipped with a frangible disk constructed to M; and (2) at least 1 oxidizing compound selected from rupture at` a predetermined pressure in order to permit the class consisting of metal peroxides, inorganic per combustion gases to escape. This constituted a gas gen chlorates and metal nitrates; said azides and said oxidiz erating unit in which the sodium azide-sodium peroxide mg compounds being present inamounts expressed by" was the gas generating grain.` The amounts of sodium gazide zand sodium ¿peroxide were suchthat "the »ratio of propellant tank 3 and an inner annular propellant 'ïtarik 4, 'the >number of nitrogen atoms-to~the valencechang'e >in »and a rocket motor 5. “Fuel `injection nlines 7 lead from the sodium peroxide upon reaction with lthe azide multi ' 'the annular propellant tanks 3 and-4 to the rocket vconi ¿plied by the number of mols of sodium peroxide was 2.7. bustion chambers 6. On îthe inside of the annular That is, in equation n/m=y the value of y was 2.7. 5 propellant tanks 8 and 9 is located chamber 8 which ‘vis In like manner, a gas generating unit is prepared using cylindrical in shape and is longitudinally disposed along 1.67 parts of sodium azide and 1 part of sodium peroxide the axis of the missile. The >gas generator grain `unit 9, to vprovide a composition in which the value of y in the of Fig. 1, is placed on the bottom of chamber >8 with equation n/m=y Ais 3. A composition prepared from 1.3 the cover containing frangible disk> 12 in a forward posi# ïparts of sodium azide and 1 part of sodium peroxide has 10 tion with respect to the missile. The heating element vfor »a y value of 2.34. A composition prepared from 2 parts igniting the contents of the gas generator unit is ,con of sodium azide and 1 part of sodium peroxide has a y Yn'ected to electrical inlet 11. The internal chamber 8 con value of 3.6 ­nects with forward chamber 10 with contacts the forward EXAMPLE II ends of- the annular propellant tanks 3 and '4. The ' 15 propellant tanks have frangible disk inserts 13 in the Following the procedure of Example I, a gas generator lforward ends connecting the chamber 10 with the propel#-V grain is prepared from 12.8 parts of barium azide, vlant tanks. The frangible disks 13 are constructed to Ba(N3)2, and 1 part of potassium perchlorate, KC104, rupture at a preselected pressure. To operate the missile, to produce a composition in which the ratio n/m=y has a current is passed through the heating element through a value of 3.6. ­ » 20 the inlet 11. This causes the composition in the gas EXAMPLE in generator to ignite. The nitrogen gas -evolved upon ­the reaction or combustion Vof the »azide-oxidizer composi ì A gas generator grain prepared as in Example I from tion ruptures the frangible disk v12 and iills chambers »8 19 parts of potassium azide, KN3, and 8.5 parts of sodium and 10. When the pressure in these chambers is built nitrate, NaNO3, together with 0.1 part of ferric oxide 25 up to a predetermined value, frangibledisks `13 are rup powder having a particle size of from 10 to about 100 tured and the gas passes into the propellant tanks 3 and microns, has an n/m=y value of 2.34. ’4. The pressure exerted by the gas causes the propellants Other metal azide-oxidizing compound gas generator to ñow through the injection lines 7 into the combustion .grains are prepared in like manner having compositions chamber 6 of the rocket motor 5. When `the rocket motor Ias in the following table in which the amounts are given 30 propellants are hypergolic as, for example, nitric _acid :in partsv by weight. and turpentine, the mixture will ignite spontaneously Table

No Metal Azide Parts Oxidizing Compound Parts Catalyst Parts nlm=y

1....­ Lithium azlde_____ 10 2. 5 l2 2. 8 4 3. 4 86 3.0 63 2. 9 2 Magnesium nitrate ______1 ______3. 1 Sodium azide. _ ___ 38 Manganese nitrate ..... __ 15 ______3. 5 Potassium azide.-. 26 Ferrie nitrate- _ _ 9 Manganese. 1. 0 2. 9 Calcium azide_ _ 16 ‘ 19 ' ______2. 3 __ Barium azide.- _ 38 13 ______3.6 _ Strontium azld _ 77 27 Zlrconium oxide 1. 0 2. 7 Barium azide. ____ 20 Lead nitrate ______11 ..... _. .

To test the operation of the gas generator units, the upon contact in the combustion chamber, producing the unit prepared as in Example I and shown in Fig. 1 was necessary thrust gases for propelling the rocket or missile. mounted on an anchored stand and fired by passing an Eñicient motor operation is obtained in this manner with electric current through the heating element 27. The 50 no deleterious effects of the nitrogen gas, which is evolved iiash powder, upon being ignited, served to ignite the from the gas generator unit, on the propulsion fuels used. gas generator grain which then burned on the surface, Gas Vgenerator grains having the compositions shown liberating nitrogen gas. The nitrogen gas upon building in the table give equally good results when employed to up suñicient pressure ruptured frangible disk 12 and was pressurize rocket engine propellant containers as de~ directed against the pickup of a pressure measuring de scribed above. vice which contained a strain gage adapted to indicate As stated hereinabove, the use of the compositions of the pressure on an oscillograph to which it is connected. this invention in gas generator grains produces «only an The pressure from the combustion gas of the composi- » inert nitrogen gas which does not aifect the fuel. Also, tion of Example I was found in this case to be 1000 l there are no corrosive products from the combustion of pounds per square inch over a period of 10 seconds. 60 the gas generator grain so that there is no deleterious The whole gas generator grain was consumed with an effects upon either the container or the rocket motor. even evolution of gas. That is, there was no fluctuation Therefore, an embodiment of this invention is a method in gas pressure, indicating that the grain burned evenly for feeding or expelling liquid propellantsv to the motor on the surface. Gas generator grains prepared as in of a missile or rocket comprising burning or reacting an Examples II and III and those having the compositions 65 azide-oxidizer composition of the type described herein» shown in the table are tested in similar manner and above to produce nitrogen gas, pressurizing the propellant give good results. container of the missile or rocket with the nitrogen gas In the operation of a rocket, a gas generator grain and thus causing the propellant to be fed to the motor of prepared as in Example I, is mounted on the inside of a the missile or rocket. ì _ fuel tank of a rocket, aircraft or missile in a position 1.0 Although the invention has been described and illus such that it is not in contact with the liquid fuel. The . trated in detail, it is to be clearly understood that the method of operation of a rocket or missile employing same is by way of illustration and example only and is the gas generator unit may be more readily described with not to be taken by way of limitation, the spirit and scope reference to Fig. 2. In this ñgure, missile 1 has a war of the invention being limited only by the terms of the _bead 2, a central section containing an outer annular 76 appended claims. 2,981,618 . . „7 I claim: ` l f 5. The composition of claim 3 wherein the alkali metal 1. A composition consisting essentially of (1) an azide azide is `sodium azide and the metal peroxide is an alkali lhaving the general formula M(N3)X wherein M is selected `metal peroxide. p p p ‘ :from the class consisting of a hydrazino radical, an am *t 6. _The composition'of claim 3 wherein the yalkali metal monium radical, an alkali metal and an alkaline earth 'azide is sodium azide and the metal peroxide is sodium metal, N is nitrogen, and x represents the valency of M, peroxide. Y ' ` ‘ .and (2) at least one oxidizing compound selected from 7. `The composition of claim3 wherein the alkali metal the class consisting of metal peroxides, inorganic perchlo azide is sodium azide, the metal peroxide is sodium >rates and metal nitrates; said azi‘des and said oxidizing peroxide and the value of y is substantially 2.7. Acompounds being present in amounts expressed by the 8. A composition consisting essentially of sodium azide 4equation n/mry, wherein n represents the number of . and sodium peroxide’in amounts such that the ratio of >azide nitrogen atoms, 14n represents the number of equiv the 'number of. azide `nitrogen atoms-to-equivalents of alents of oxidizing compounds, and y has a numerical sodium peroxide is substantially 2.7, and from about 0.1 `value of from about 2.3 _to about 3.6. to about 3 weight percent of a compatible burning cat~ 2. A composition consisting essentially of (1) an azide alyst selected from the class consisting of powdered car -having the lgeneral formula M(N3)X wherein M is an bon, phosphorus, sulfur and metal »and metalloid powders alkali metal, N is` nitrogen, and x represents the valence and their oxides of copper, magnesium, boron, aluminum, »of M, and (2) at least _one oxidizing compound selected zirconium, vanadium, antimony, manganese, iron, cobalt, from the class consisting of metal peroxides, inorganic nickel, ferric‘oxide and silica. perchlorates and metal nitratesg said azides and said oxidizing compounds being present in amounts expressed References Cited in the file of this patent by the equation n/m=y, wherein n represents the num UNITED> STATES PATENTS ber of azide nitrogen atoms, m represents the number 2,001,212 Olsen et al ______May 14, 1935 of equivalents of oxidizing compounds, and y has a uu 2,004,505 MeNua ______June 11, 1935 'mercial value of from about 2.3 to about 3.6. 25 2,410,801 Andrieu; ...... _s ______Nov. 12, 1946 3. A composition consisting essentially of (1) -an azide having the general formula M(N3) wherein M is an alkali FOREIGN PATENTS metal and N is nitrogen, and (2) a metal peroxide; said 310,049 ’ Germany ______Apr. 14, 1921 alkali `metal azide and said peroxide being present in 362,048 Great Britain ______Dec. 3, 1931 amounts expressed by the equation nlm=y wherein n is 30 'the number of equivalents of metal peroxide, and y has a OTHER REFERENCES numerical value of from about 2.3 to about 3.6. Military , TM~l9l0/TO11A­­1­34, Depts. of 4. The composition of claim 3 wherein the metal the Army and Air Force, April 1955, pages 95-96. (Copy peroxide is an alkali metal peroxide. in Sci. Lib.)