United States Patent [19] 1111 3,883,373 Sidebottom [45] May 13, 1975

[54] GAS GENERATING COMPOSITIONS [56] References Cited [75] Inventor: Eric William Sidebottom, Otterburn UNITED STATES PATENTS Heights, Quebec. Canada 2,981,616 4/1961 Boyer ...... 149/35 [731 2964292 4:22: §::1;"::,:%i';;;~ 112/22 9 Montreal’ Quebm Canada 3,797,854 3/1974 POOle et al ...... 149/35 x [22] Filed: July 2, 1973 _ Primary Examiner—Stephen J. Lechert, Jr. [2]] Appl' NO" 375’654 Attorney, Agent, or Firm—Alexander O. Mclntosh

[30] Foreign Application Priority Data [57] ABSTRACT July 24, i972 United Kingdom ...... 34481/72 A gas generating composition having as ingredients an . _ alkali or alkaline earth metal azide, an oxidizing com [52] US. Cl...... 149/6; 149/35, 149/37, pound, an Oxide such as silica or alumina, and option_ 149/40; 149/41; 149/42; 149/43;_ 149/45; ally, a metal such as silicon or aluminum. The compo 149/75’ 149/77 sition is useful as a source of gas to in?ate bags used

Int...... _ . ..' . . . I ...... _ . . .. as restraint Systems for the protection of automobile [58] Field of Search ...... 149/6, 35, 37, 75, 40, passengers. 149/77, 45, 36, 42, 41, 43 8 Claims, No Drawings 3,883,373 1 2 GAS GENERATING COMPOSITIONS and zinc, in proportion sufficient to react with the me tallic residue of the reaction between (1) and (2). This invention relates to a composition of matter suit The use of a mixture of an oxide and a metal as ingre able for generating gases. dients of the composition provides a means of adjusting As a safety measure, in?atable restraint systems have the burning rate. Compositions containing only oxide been devised to protect the passengers of automobiles as ingredient (3) burn more slowly than compositions in the event of collision. These systems commonly con having only metal as ingredient (3). When (3) is a mix sist of a bag located in front of the passengers which is ture of silica and silicon, variation of the proportions of caused to inflate in response to rapid decelaration of these two components provides a range of burning the automobile. 10 rates extending from about 1 10 milliseconds with silica It is known to in?ate the bag through the action of only to about 1 1 milliseconds with silicon only, depend compressed gas released from a storage vessel. How ing on the size and configuration of the propellant ever, the use of compressed gas for this purpose entails mass. certain disadvantages. A large heavy-walled vessel is The ingredients of the gas generating composition required to store the gas under a pressure of about may be mixed together in the form of solid particles and ignited by means of a hot wire or a squib. Alterna 3,000 pounds per square inch. It is also necessary to en sure that the gas storage vessel remain sealed over long tively, the composition may be employed in two sepa rate portions, a ?rst portion comprising the azide and period of time, ready for service in case of an accident. the oxidizing compound, and a second portion com It is also known to in?ate the bag through the action prising the metallic oxide. The second portion will then of gas developed by a burning propellant or pyrotech be placed as a sheath about the ?rst portion, or be nic composition. Block powder has been employed as placed in the outlet zone of the vessel carrying the gas the gas generating composition but has the disadvan generating composition. ' tage that the products of combustion are noxious. As is known in the art, the gas generating composi Compositions containing alkali metal azides have ad 25 tion will be enclosed in a vessel that communicates with vantages as means for gas generation since the product the in?atable bag of the restraint system. Normally a of combustion is mainly gas, However, a com baf?e and/or ?ltering device will be positioned in the position consisting of an alkali metal azide and an ox gas duct between the gas generating vessel and the in ygencontaining oxidizing compound produces, in addi ?atable bag for the purpose of restricting the ?ow of tion to nitrogen, a certain amount of toxic, corrosive 30 solid products into the bag. alkali metal oxide, Such a composition is disclosed in _ The reaction of the gas generating composition can US. Pat. No. 2,981,616 for use as a source of gas for be represented by the equation: pressurizing rocket propellant tanks. Pyrotechnic com positions containing an alkali metal azide, oxidizing 2NaN3 + $102 + o —> N212SiO3 + 6N2 compound and a fuel such as boron or silicon are dis 35 where the azide is , the oxide is silica and closed in US. Pat. No. 3,122,462. When used as oxygen is obtained from a suitable oxidizing com sources of gas, however, these pyrotechnic composi pound. In the case where the azide is sodium azide, the tions, depending upon the proportions of the ingredi oxide is silica and- potassium perchlorate is the oxidiz ents, may exhibit a high burning rate, approaching det ing compound the equation will be: onation. A gas generating composition suitable for in?ating an automobile restraint system has now been found which When a mixture of silica and silicon is employed as avoids the disadvantages of prior art propellant and py ingredient (3) the reaction can be represented by the rotechnic compositions. The novel composition con equation: tains an alkali metal or alkaline earth metal azide, an 45 SNaN:3 + mSi + (4—m)SiO2 + (1+0.5m) KClO, —> oxidizing compound and an oxide of silicon, alumin 4Na2SiO3 + (1+0.5m)KCl + 12N2 ium, titanium, tin or zinc with or without admixture The silicate formed will depend upon the composition with silicon, aluminum, titanium, tin or zinc metal, said of the azide employed. With , for example, oxide, and metal if present, being in amount sufficient the silicate will be BaSiO3. It also can be expected that to react with metallic oxides produced during the de in the presence of the oxidizing compound the reaction composition of the azide. The composition produces may produce complex silicates. nitrogen gas at a rate suitable for in?ation of an auto Suitable azide ingredients of the gas generating com mobile restraint bag and the solid products of gas form positions of this invention are , sodium az ing reaction are non-toxic and non-corrosive. ide, , azide, cesium azide, cal It is thus the primary object of the invention to pro 55 cium azide, magnesium azide, strontium azide and bar vide a gas generating composition wherein the products .ium azide. of the gas generating reaction are non-toxic and non , Oxidizing compounds suitable as ingredients of the corrosive. Additional objects will appear hereinafter. gas generating compositions include metal peroxides The gas generating composition of this invention such as sodium peroxide, potassium peroxide, rubidium comprises ( l ) an azide of an alkali metal or an alkaline peroxide, cesium peroxide, calcium peroxide, stron earth (2) an oxidizing compound in proportion suffi tium peroxide, and varium peroxide; inorganic perchlo cient to react completely with said azide with the liber rates such as lithium perchlorate, sodium perchlorate, ation of nitrogen gas therefrom, and (3) an oxide se potassium perchlorate, rubidium perchlorate, magne sium perchlorate, calcium perchlorate, strontium per lected from the group consisting of silicon oxide, alumi 65 num oxide, titanium oxide, tin oxide and zinc oxide, chlorate, barium perchlorate, ferric perchlorate and with or without admixture with a metal selected from cobalt perchlorate; and metal nitrates such as lithium the group consisting of silicon, aluminum, titanium, tin nitrate, sodium nitrate, potassium nitrate, copper ni 3,883,373 3 4; trate, silver nitrate, magnesium nitrate, barium nitrate, EXAMPLE 4 zinc nitrate, aluminum nitrate, thallium nitrate, stannic nitrate, bismuth nitrate, manganese nitrate, ferric ni One 20 gram charge of the composition in Example trate, ferrous nitrate and nickel nitrate. 3 was ignited in a ?eld test, by means of an S1 19 squib. Oxides suitable as ingredients of the gas generating The material required about 2 seconds for complete compositions include silicon dioxide (silica) aluminum combustion. oxide, titanium dioxide, tin oxide, and zinc oxide. Met EXAMPLE 5 als suitable as ingredients of the compositions include Two 5 gram charges of the material in Example 3 silicon, aluminium, titanium, tin and zinc. It has been found that the impact sensitivity of the were placed in canisters and ignited in a closed high composition is reduced by including as ingredient, pressure vessel. Ignition was achieved by means of a fumed silica coated with a water repellent such as a si hot wire. A peak pressure of approximately 900 psi. lane. This type of hydrophobic silica is described at was achieved in 22 milliseconds after the initiation of page 39 of the Sept. 8, 1971 issue of Volume 109 of combustion. Chemical Week. The preferred portion of coated The solid products of two combustion experiments fumed silica is an additional 2 percent by weight. How were recovered and analysed. The results indicated that 97 percent of the silicon metal had been converted ever, the coated fumed silica may replace the total oxide content of the composition. in a water soluble silicate. The proportions of the azide and oxidizing com EXAMPLE 6 pound are chosen so that the azide will be completely Two 20 gram charges of the material in Example 3 reacted to form gaseous nitrogen. Azides are toxic ma were placed in canisters and ignited in a closed high terials and it is undesirable to inject unreacted azide pressure vessel. Ignition was by means of a hot wire. A into the in?atable restraint bag. The proportion of peak pressure of approximately 9,000 p.s.i. was oxide and when present the metal is chosen so that the 25 achieved in l 1 milliseconds after initiation of combus metallic residue of the reaction between the azide and tion. the oxidizing compound will react to form the non‘ toxic solid compounds. When the oxide is silica and the EXAMPLE 7 metal silicon, the compounds formed will be silicates. Five 20 gram charges of material in Example 1 were In the case of other oxides and metals there will be placed in canisters and ignited in a closed pressure ves formed oxygen-containing compounds such as alumi sel by means of a hot wire. A peak pressure of 2,500 nates, titanates, etc. p.s.i. was achieved in a combustion time of 110 milli The ingredients of the gas generating composition seconds. Some ignition delay was observed using the are employed in particulate form. ‘Although particle 35 hot wire method of ignition. The above figure of 110 size is not apparently critical, it is convenient to employ milliseconds is actual burn time, and does not include material in the particle size less than 100 mesh Tyler the delay period. screen size. The solid products of combustion of three of these The gas generating compositions of the present on ignitions were collected and analysed. Analysis indi vention provides means for generating non-toxic gas by 40 cated that 87% of the silica originally present in the means of a reaction that produces non-toxic solid prod propellant had been converted to a water soluble sili ucts. cate. The invention is additionally illustrated by the follow mg Examples but its scope is not limited to the embodi EXAMPLE 8 ments shown therein. 45 Three 20 gram charges of a composition containing sodium azide, aluminum and potassium chlorate in the EXAMPLE 1 molar proportions 2:2:1 were placed in canisters and Three 40 gram charges of a composition‘ containing ignited in a closed high pressure vessel. ignition was by sodium azide, silicon dioxide and potassium perchlo means of a hot wire. The samples had an average com rate in the molar proportions 814:1 were placed in can~ 50 bustion time of 14 milliseconds. The residue of com isters and ignited in a field test using a No. 8 electric bustion was extracted with water and the water extract blasting cap to initiate ignition. The material burned in analyzed for sodium and aluminum. The atomic ratio slightly less than 1 second. Al/Na is given in table 1. it can be seen that the conver sion of aluminum into sodium aluminate NaA1O2 is on EXAMPLE 2 55 average 52 percent efficient, since complete conver One 20 gram charge of the above formulation was ig sion would provide a Al/Na ratio of 1.0. nited by an S1 19 squib. Material required about 3 sec EXAMPLE 9 onds for complete combustion. Three 20 gram charges of a composition containing EXAMPLE 3 sodium azide. alumina (A1203) and potassium perchlo Three 40 gram charges of a composition containing rate in the molar proportions 8:4:l were placed in can sodium azide, silicon and potassium perchlorate in isters and ignited in a closed high pressure vessel. Igni molar proportions 8:4:3 were placed in canisters and tion was by means of a hot wire. The samples had an ignited in a field test using a No. 8 electric blasing cap average combustion time of 130 milliseconds. The resi 65 to initiate ignition. The material burned extremely due was analyzed as in Example 8. The results are given quickly at a rate only fractionally less than a detona in Table 1. It can be seen that the conversion into so tion. dium aluminate is on average 48 percent efficient. 3,883,373 5 6 1. an alkali metal azide or an alkaline earth metal az TABLE] ide, 2. an oxidizing compound in proportion sufficient to Atomic Ratio Al/Na Average Al/Na react completely with said azide with the liberation Example 8 5 of nitrogen therefrom, and 3. an oxide selected from the group consisting of sili Example 9 con dioxide, aluminum oxide, titanium dioxide, tin oxide and zinc oxide, with or without admixture with a metal selected from the group consisting of silicon, aluminum, tin and Zinc, said oxide and metal being in proportion sufficient to react with EXAMPLE 10 all the metallic residue of the reaction between ( l ) The effect of a hydrophobic silica ingredient on the and (2). sensitivity of the following compositions; sodium azide, 2. A gas generating composition as claimed in claim silicon, potassium perchlorate in molar ratio 814:3 and 15 1 wherein the azide is selected from the group consist sodium azide, silicon dioxide, potassium perchlorate in ing of lithium azide, sodium azide, potassium azide, ru molar ratio 8:4:] was measured by adding to the com bidium azide, cesium azide, calcium azide, magnesium positions an additional 2 percent by weight of the fol azide, strontium azide and barium azide. lowing materials: 3. A gas generating composition as claimed in claim 1. fumed silica having a silane coating (Silanox 101) 20 1 wherein the oxidizing compound is a metal peroxide Silanox is a registered trade mark. Silanox 101 has selected from the group consisting of sodium peroxide, a surface area of 225 sq. meters/gram and a pH of potassium peroxide, rubidium peroxide, cesium perox 8-10. ide, calcium peroxide, strontium peroxide and barium 2. precipitated silica coated with polysiloxane. 25 peroxide. a. QUSO WR 50 4. A gas generating composition as claimed in claim b. QUSO WR 82 1 wherein the oxidizing compound is an inorganic per QUSO is a registered trade mark. WRSO has a sur chlorate selected from the group consisting of lithium face area of 130 sq. meters/gram and a pH of 8.5. perchlorate, sodium perchlorate, potassium perchlo WR 82 has a surface area of 120 sq. meters/gram rate, rubidium perchlorate, magnesium perchlorate, and a pH of 11.0. calcium perchlorate, strontium perchlorate, barium The sensitivity was measured with a drop hammer using the height at which zero ignition occurred in 20 perchlorate, ferric perchlorate and cobalt perchlorate. 5. A gas generating composition as claimed in claim drop tests. The results are shown in TABLE II. 1 wherein the oxidizing compound is a metal nitrate se TABLE ll 35 lected from the group consisting of lithium nitrate, so~ dium nitrate, potassium nitrate, copper nitrate, silver Composition NaNJSi/KClO, NaN;,/SiO~:/KClO4 nitrate, magnesium nitrate, barium nitrate, zinc nitrate, 8/4/3 8/4/l aluminum nitrate, thallium nitrate, stannic nitrate, bis Hydrophobic muth nitrate, manganese nitrate, ferric nitrate, ferrous silica added nitrate and nickel nitrate. none 7.5 inches 7.5 inches 2% of 1 12.5 inches 12.5 inches 6. A gas generating composition as claimed in claim 2% of 2(a) 7.5 inches 7.5 inches 1 including as ingredient fumed silica coated with a 2% of 2(b) 7.5 inches 7.5 inches water repellent. 7. A gas generating composition as claimed in claim It can be seen that fumed silica coated with a silane 6 wherein the water repellant is a silane. acts as a desensitizer. 8. A gas generating composition as claimed in claim What we claim is: 6 wherein the fumed silica ingredient comprises 2% by l. A. gas generating composition comprising a mix weight of the composition. ture of particles of the following ingredients * * * * >l<

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