AU663659B2 - Mixed fuel gas generant compositions - Google Patents

Description

AUSTRALIA

Patents Act 6 6 659 COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: I Name of Applicant: Morton International, Inc.

Actual Inventor(s): Robert D. Taylor Thomas M. Deppert Address for Service: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Invention Title: MIXED FUEL GAS GENERANT COMPOSITIONS Our Ref 387353 POF Code: 1436/1436 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): -1-

PATENT

2363-21-00 MIXED FUEL GAS GENERANT COMPOSITIONS The present invention is directed to non-azide gas generant compositions useful, for example, to provide inflation for automobile air bag restraint systems.

BackQround of the Invention: Gas generant compositions for inflating automobile air bag restraint systems presently predominantly use sodium azide as the S.fuel. Because of toxicity problems with respect to sodium azide Sand instability problems due to reaction of sodium azide with heavy metal contaminants, gas generants based upon alternative fuels have been proposed, although none, so far, has replaced .sodium azide compositions to any appreciable extent.

a.One type of alternative fuel comprises tetrazoles, triazoles and their salts, as described, for example in U.S. Patent No.

4,909,549, the teachings of which are incorporated herein by reference. U.S. Patent No. 5,139,588, the teachings of which are incorporated herein by reference, describes mixtures of .**",tetrazoles and alkali metal salts of tetrazoles in amounts [sufficient to reduce amounts of toxic oxides, such as NOx and CO, in the combustion gases. The mixture of non-salts and salts of tetrazoles combines advantageous features of each to provide an improved gas generant composition. Non-salts have the advantage in that the only combustion products attributed to the non-salt tetrazoles are gases, whereas the tetrazole salts also produce undesirable slag in the form of metal oxides. On the other hand, production of toxic oxides is temperature dependent, being produced in greater amounts at the higher combustion temperatures 1 ;;2 4

PATENT

2363-21-00 of the non-salt tetrazole compounds. Accordingly, salts, such as tetrazole salts, are used in conjunction with non-salt tetrazole compounds to control combustion temperature and thereby provide high gas output, without generation of high levels of toxic oxides.

An additional problem with gas generant compositions containing salts of tetrazole compounds, not discussed in U.S.

Patent No. 5,139,588, is that such salts are hygroscopic. While care is taken in producing gas generant compositions to maintain them in a moisture-free environment and while gas generant S compositions are generally maintained in a hermetically sealed Scontainer, any failure of such precautions may seriously affect the performance of a gas generant composition containing a hygroscopic fuel.

1Ej, Another class of fuels suitable as azide alternatives are described in U.S. Patent No. 5,015,309 to Wardle et al. The fuels described therein are salts of 5-nitrobarbituric acid, 5-nitroorotic acid and 5-nitrouracil (which doesn't form a salt).

Of these, 5-nitrouracil is disfavored, having a high burning ::temperature. The non-salt forms of 5-nitrobarbituric acid and nitroorotic acid might similarly function as fuels, but, like nitrouracil, would have an unfavorably high combustion temperature. In fact, the free acid (non-salt) forms of this .class of fuel is considered unfavorable relative to tetrazoles and triazoles in that they produce less gas on a mole per gram basis and burn at higher temperatures.

Summary of the Invention: In accordance with the present invention, a gas generant composition comprises between about 30 and about 65 wt% of fuel, between about 5 and about 75 wt% of the fuel comprising a nonsalt component selected from the group consisting of 2

I

i) aminotetrazole, tetrazole, bitetrazole, triazole and mixtures thereof and between about 25 and about 95 wt% of the fuel comprising an alkali or alkaline earth metal salt of nitrobarbituric acid, 5-nitroorotic acid or mixtures thereof; and between about 45 and about 65 wt% of an oxidizer.

Detailed Description of Certain Preferred Embodiments: The azole compound, the non-salt form of amino tetrazole, tetrazole, bitetrazole, triazole or mixture thereof provided, upon combustion with the oxidizer, a high volume of 0J generant gas which is high in nitrogen (N 2 content. This fuel component produces only gases as combustion products.

The alkali metal or alkaline earth metal salt of i, 5-nitrobarbituric acid and/or 5-nitroorotic acid is a fuel component which lowers the combustion temperature of the composition (relative to use of the azole component alone).

SThese salts are advantageous relative to azole salts in being V '^non-hygroscopic. Thus, even if precautions against moisture fail, the composition of the present invention should continue to function efficiently as a gas generant.

It is generally desirable to produce as high a volume of gas possible while achieving a combustion temperature which is preferably not above about 200 0 K so as to minimize formation of S' toxic oxides. To this end, the mixture is desirably as rich in azole compound relative to the salt of 5-nitrobarbituric acid and/or 5-nitroorotic acid as is consistent with achieving a desirably low combustion temperature.

I The oxidizer includes at least one ammonium, alkali metal or alkaline earth metal nitrate, perchlorate or chlorate or a transition metal oxide.

The cations of the 5-nitrobarbituric acid salts and nitroorotic acid salts and the cations of the oxidizer component

PATENT

2363-21-00 preferably include both alkali metal cations and alkaline earth metal cations. The former, upon combustion, produce liquid slag components; the latter solid components. The combination of liquid and solid slag components promotes formation of clinkers which are easily filterable.

It is preferred to add SiO 2 up to about 10 wt%, preferably at least 0.5 wt%, to scavenge K 2

CO

3 KOH, K20 and related products from the combustion products, thereby forming K 2 SiO 3 a liquid slag component. The silica may be provided as particulates or as a sole or joint component of fibers.

S. To promote combustion, up to about 10 wt% of a catalyst, preferably at least about 0.1 wt%, may be used. Catalysts may include, for example, transition metal oxides, transition metal chromates, transition metal vanadates, transition metal 1 5 manganates, boron hydrides and mixtures thereof.

It is frequently desirable to provide a gas generant in pellet form. If the composition does not hold together by compaction alone, a binder in an amount of up to about 10 wt% may be included, typically at least about 1 wt% being used. Binders include, but are not limited to molybdenum disulfide, graphite, polytetrafluoroethylene, Viton® (copolymer of vinylidene fluoride and hexfluoro propylene), nitrocellulose, polysaccharides, polyvinylpyrrolidones, polycarbonates, sodium silicate, calcium stearate, and magnesium stearate.

Additional components, which may be used at levels totalling about 10 wt% include, but are not limited to graphite fibers, alumina fibers, alumina/silica fibers, boron oxide and titanium dioxide.

The invention will now be described in greater detail by way of specific examples.

Examples Compositions formulated as per the table below, were 4

PATENT

2363-21-00 prepared by slurry blending the solids with about 25% to water, drying the mixture thoroughly at 80 0 C under vacuum mmHg) and screening the composition through a 16 mesh screen.

Pellets were prepared by compression molding at 40,000 psi. The table also list combustion temperature and gas output.

Formulations A, B, D, and E in wt% are given as examples.

Formulations C, F, G, H and I are given for comparison.

Examples A B C KDL 42.62 39.42 48.89 4.69 7.08 Sr(NO 3 2 46.64 47.89 44.12 I 1 SiO 2 6.05 5.61 6.99 100.00 100.00 100.00 Combustion Temp. 1675 1765 1524 Moles of gas per 100Og of generant 1.806 1.856 1.652 Examples f D E F KNOA, 35.17 22.54 47.54 S 5-AT 9.57 19.72 Sr(NO 3 2 50.92 56.32 43.04 SiO 2 4.34 1.42 9.42 100.00 100.00 100.00 Combustion Temp. (OK) 1584 2000 1329 Moles of gas per 100g of generant 1.870 2.150 1.571 i 1 i l JI I 1

PATENT

2363-21-00 Examples Sr(NO 3 2 SiO 2 35.73 62.27 2.00 100.00

H

34.27 59.73 6.00 100.00 2609 2.315 Combustion Temp. (OK) Moles of gas per 100g of generant 33.10 58.90 8.00 100.00 2571 2.346 2661 2.417 r .t r KDL is potassium salt of nitrobarbituric acid (potassium diliturate).

KNOA is potassium salt of 5-nitroorotic acid.

5-AT is Formulations A, B, D and E make a filterable slag, whereas by comparison formulations C and F in the above Table do not. Also, formulations A, B, D and E burn cooler than 5-AT (examples G, H and I) alone and produce more gas than either KDL or KNOA alone.

9* tt *aL 6

Claims (6)

1. A gas generant composition including between 30 and 65 wt% of fuel, between 5 and 75 wt% of said fuel selected from aminotetrazole, tetrazole, bitetrazole and triazole, and between 25 and 95 wt% of said fuel selected from alkali or alkaline earth metal salts of 5-nitrobarbituric acid, 5-nitroorotic acid and mixtures thereof, and between 45 and 65 wt% of an oxidizer.

2. A composition according to claim 1 wherein said oxidizer includes at least one ammonium, alkali metal or alkaline earth metal nitrate, perchlorate or chlorate or transition o metal oxide. o C

3. A composition according to claim 1 or claim 2 further including between 0.5 and 4 n wt% Si02.

4. A composition according to any one of claims 1 to 3 further including between 0.1 and 10 wt% of a catalyst selected from the group consisting of transition metal oxides, S transition metal chromates, transition metal vanadates, transition metal mangranates and mixtures thereof.

5. A composition according to any of claims 1 to 3 further including between 1 and wt% of a binder.

6. A composition according to claim 1 substantially as hereinbefore described with reference to any of the examples. DATED: 5 July 1995 PHILLIPS ORMONDE FITZPATRICK Attorneys For: MQRTON INTERNATIONAL, INC. 4 14 PATENT 23 63-2 1-00 MIXED FUEL CAS GENERANT COMPOSITIONS Abstract of the-Disclosure In a gas generant composition comprising fuel and oxidizer, the fuel is a mixture of non-salt forms of azoles and alkali metal and/or alkaline earth metal salts of 5-nitrobarbituric acid and/or 5-nitroorotic acid. 9 C s0p23300we 0900 00C*tC 0 0~*0SC C 9* I 9t