Explosive and thermic compositions or charges – Containing hydrazine or hydrazine derivative
Reexamination Certificate
1998-06-05
2001-05-15
Miller, Edward A. (Department: 3641)
Explosive and thermic compositions or charges
Containing hydrazine or hydrazine derivative
C149S046000, C149S047000, C149S060000, C149S061000
Reexamination Certificate
active
06231702
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a non-azide based gas generating composition. The gas generating composition of the present invention is particularly useful for inflating an inflatable vehicle occupant protection device.
BACKGROUND OF THE INVENTION
Azide-based gas generating compositions for generating gas to inflate an inflatable vehicle occupant protection device have the advantage that they produce non-toxic nitrogen gas during combustion and produce gas at relatively low gas temperatures.
Non-azide based gas generating compositions, in contrast, typically produce gas at temperatures well above the temperature of gas produced by azide-based gas generating compositions with some approaching 4000° K. While these non-azide based gas generating compositions potentially are thermodynamically efficient, they present heat management problems.
For instance, it may be necessary, because of the high temperatures, to manufacture certain components of the vehicle occupant protection device of more expensive materials that are resistant to the high temperature gas which is generated. In addition the non-azide based gas generating compositions tend to produce reaction products which may be in the vapor phase at high temperature and thus more difficult to filter.
Various attempts to cool the non-azide based gas generating compositions include adding chemical coolants to the compositions. Chemical coolants, however, tend to add to the volume of the gas generating material required without increasing the gas output. This reduces the gas output per volume of gas generating material in an amount dependent upon the amount of coolant added.
Mechanical approaches to cooling the products of combustion of gas generating compositions involve using filters which function as both a heat exchanger and a particulate trap. However, the gas volume output tends to drop dependent upon the heat loss to the filter, especially if the particulate trapping in the filter is highly efficient.
SUMMARY OF THE INVENTION
The present invention resides in a gas generating composition which comprises an organic fuel and an oxidizer wherein the oxidizer is phase stabilized ammonium nitrate. The phase stabilizer for the ammonium nitrate is an alkali metal or alkaline earth metal salt. The composition further comprises an ammonium salt coolant selected from the group consisting of an ammonium halide, ammonium sulfate, and ammonium sulfamate. A preferred ammonium halide is ammonium chloride (NH
4
Cl). The amount of ammonium salt coolant present in the gas generating composition is an amount effective, on combustion, to produce a reaction product of the anion of the ammonium salt coolant and the cation of the alkali metal or alkaline earth metal phase stabilizer. The ammonium salt coolant reacts with the alkali metal or alkaline earth metal salt in an endothermic reaction which reduces the combustion temperature of the combustion gas product. The combustion gas product is substantially free of alkali metal or alkaline earth metal oxide.
The ammonium salt coolant is in effect a fuel component, producing on combustion only gas or vapor phase products, thus achieving an increased gas output per unit volume of gas generating material used.
Preferably, the gas generating composition of the present invention also comprises a sinter-forming material which is present in the composition in an amount effective to cause liquid particles of the reaction product to coalesce into an easily filterable slag. Preferred sinter-forming materials are silicon dioxide (SiO
2
) and aluminum oxide (Al
2
O
3
)
In an embodiment of the present invention, the mol ratio of the alkali metal or alkaline earth metal salt to ammonium salt coolant is about 1:1 for substantially complete reaction of the anion of the ammonium salt coolant with the alkali metal or alkaline earth metal cation of the phase stabilizer.
Preferably, the gas generating composition is balanced for substantially complete reaction of carbon in the organic fuel with oxygen in the oxidizer to produce carbon dioxide.
The present invention also resides in an inflatable vehicle occupant protection device which comprises an inflator for generating gas to inflate the protection device using the foregoing gas generating composition.
DESCRIPTION OF PREFERRED EMBODIMENTS
For purposes of the present application, the term “organic fuel” includes salts of organic fuels.
The gas generating composition of the present invention comprises a non-azide organic fuel, which can be any non-azide organic fuel typically used in a gas generating composition. Examples of organic fuels useful in the present invention are: cyanamides such as dicyandiamide and salts thereof; tetrazoles such as 5-amino-tetrazole (5-AT), and derivatives and salts of tetrazoles; carbonamides such as azo-bis-dicarbonamide and salts thereof; triazoles such as 3-nitro-1,2,4-triazole-5-one (NTO) and salts thereof; guanidine and derivatives thereof such as nitroguanidine; salts of guanidine and guanidine derivatives such as triaminoguanidine nitrate (TAGN) or guanidine nitrate (GN); tetramethyl ammonium nitrate; urea and urea salts; triazines and tetrazines such as trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetrazine (HMX); and combinations of such fuels.
The amount of fuel in the gas generating composition is that amount necessary to achieve sustained combustion of the gas generating composition. The amount can vary depending upon the particular fuel involved and other reactants. A preferred amount of fuel is in the range of about 10% to about 55% based on the weight of the gas generating composition.
The gas generating composition of the present invention also comprises phase stabilized ammonium nitrate as an oxidizer for the fuel. The amount of phase stabilized ammonium nitrate is that amount necessary to achieve sustained combustion with the fuel. A preferred amount of phase stabilized ammonium nitrate is in the range of about 30% to about 85% based upon the weight of the gas generating composition.
By the use of ammonium nitrate as the oxidizer for the fuel, a relatively smoke free combustion gas product is obtained. The products of combustion of the fuel and ammonium nitrate primarily are nitrogen, water, and carbon dioxide.
The phase stabilizer for the ammonium nitrate is an alkali metal or an alkaline earth metal salt. The stabilization of ammonium nitrate is necessary to avoid volumetric and structural changes associated with Phase IV ←→Phase III structural transitions due to the exposure of the gas generating composition to ambient temperature changes. Examples of alkali metal or alkaline earth metal salts which may be used include nitrates, nitrites, peroxides, and dinitramides. The amount of the phase stabilizer is an effective amount to stabilize ammonium nitrate and is up to about 15% based upon the weight of ammonium nitrate. This stabilization of ammonium nitrate is well known.
A critical component of the present invention is an ammonium salt coolant selected from the group consisting of an ammonium halide, an ammonium sulfate and an ammonium sulfamate. A preferred ammonium salt coolant is ammonium chloride (NH
4
Cl).
The amount of ammonium salt coolant in the gas generating composition is preferably that amount which provides approximately a 1:1 mol ratio with the alkali metal or the alkaline earth metal salt stabilizer. This results in substantially complete reaction of the anion of the ammonium salt coolant with the alkali metal or alkaline earth metal cation of the phase stabilizer to produce a combustion gas product which is substantially free of alkali metal or alkaline earth metal oxide. A preferred amount of ammonium salt coolant is in the range of 1% to about 10% based on the weight of the gas generating composition.
In the present invention, the ammonium salt coolant reacts with the alkali metal or alkaline earth metal salt in an endothermic reaction which reduces the temperature of the combustion gas product. It was found that when the ammonium salt coolant is present
Miller Edward A.
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
TRW Inc.
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