Explosive and thermic compositions or charges – Metal or alloy or metalloid – each in particulate form – with... – With nitrated organic compound
Reexamination Certificate
1998-01-22
2004-06-15
Felton, Aileen B. (Department: 3641)
Explosive and thermic compositions or charges
Metal or alloy or metalloid, each in particulate form, with...
With nitrated organic compound
C149S037000, C149S043000, C149S045000, C102S205000
Reexamination Certificate
active
06749702
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to gas generating compositions, such as those used in “air bag” passive restraint systems, and, in particular, to autoignition compositions that provide a means for initiating combustion of a main pyrotechnic charge in a gas generator or pyrotechnic device exposed to temperatures significantly above the temperatures at which the unit is designed to operate.
BACKGROUND OF THE INVENTION
One method commonly used for inflating air bags in vehicle passive restraint systems involves the use of an ignitable gas generator that generates an inflating gas by an exothermic reaction of the components of the gas generator composition. Because of the nature of passive restraint systems, the gas must be generated, and the air bag deployed in a matter of milliseconds. For example, under representative conditions, only about 60 milliseconds elapse between primary and secondary collisions in a motor vehicle accident, i.e., between the collision of the vehicle with another object and the collision of the driver or passenger with either the air bag or a portion of the vehicle interior.
In addition, the inflation gas must meet several stringent requirements. The gas must be non-toxic, non-noxious, must have a generation temperature that is low enough to avoid burning the passenger and the air bag, and it must be chemically inert so that it is not detrimental to the mechanical strength or integrity of the bag.
The stability and reliability of the gas generator composition over the life of the vehicle are also extremely important. The gas generator composition must be stable over a wide range of temperature and humidity conditions, and must be resistant to shock, so that it is virtually impossible for the gas generator to be set off except when the passive restraint system is activated by a collision.
Typically, the inflation gas is nitrogen, which is produced by the decomposition reaction of a gas generator composition containing a metal azide. One such gas generator composition is disclosed in Reissued U.S. Pat. No. Re. 32,584. The solid reactants of the composition include an alkali metal azide and a metal oxide, and are formulated to ignite at an ignition temperature of over about 315° C.
The gas generator composition is typically stored in a metal inflator unit mounted in the steering wheel or dashboard of the vehicle. Several representative inflator units are disclosed in U.S. Pat. Nos. 4,923,212, 4,907,819, and 4,865,635. The combustion of the gas generator composition in these devices is typically initiated by an electrically activated initiating squib, which contains a small charge of an electrically ignitable material, and is connected by electrical leads to at least one remote collision sensing device.
Due to the emphasis on weight reduction for improving fuel mileage in motorized vehicles, inflator units are often formed from light weight materials, such as aluminum, that can lose strength and mechanical integrity at temperatures significantly above the normal operating temperature of the unit. Although the temperature required for the unit to lose strength and mechanical integrity is much higher than will be encountered in normal vehicle use, these temperatures are readily reached in, for example, a vehicle fire. As the operating pressure of standard pyrotechnics increases with increasing temperature, a gas generator composition at its autoignition temperature will produce an operating pressure that is too high for a pressure vessel that was designed for minimum weight. Moreover, the melting point of many non-azide gas generator compositions is low enough for the gas generator composition to b molten at the autoignition temperature of the composition, which can result in a loss of ballistic control and excessive operating pressures. Therefore, in a vehicle fire, th ignition of the gas generator composition can result in an explosion in which fragments of the inflation unit are propelled at dangerous and potentially lethal velocities.
To prevent such explosions, air bags have typically included an autoignition composition that will autoignite and initiate the combustion of the main gas generating pyrotechnic charge at a temperature below that at which the shell or housing begins to soften and lose structural integrity. The number of autoignition compositions available in the prior art is limited, and includes nitrocellulose and mixtures of potassium chlorate and a sugar. However, nitrocellulose decomposes with age, so that the amount of energy released upon autoignition decreases, and may become insufficient to properly ignite the main gas generator charge. Moreover, prior art autoignition compositions have autoignition temperatures that are too high for some applications, e.g., non-azide auto air bag main charge generants.
Therefore, a need exists for a stable autoignition composition that is capable of igniting the gas generator composition at a temperature that is sufficiently low that the inflator unit maintains mechanical integrity at the autoignition temperature, but which is significantly higher than the temperatures reached under normal vehicle operating conditions.
SUMMARY OF THE INVENTION
The present invention relates to an autoignition composition for safely initiating combustion in a main pyrotechnic charge in a gas generator or pyrotechnic device exposed to flame or a high temperature environment. The autoignition compositions of the invention comprise a mixture of an oxidizer and a powdered metal fuel, where the oxidizer comprises at least one of an alkali metal or an alkaline earth metal nitrate, a complex salt nitrate, such as Ce(NH
4
)
2
(NO
3
)
6
or ZrO(NO
3
)
2
, a dried, hydrated nitrate, such as Ca(NO
3
)
2
·4H
2
O or Cu(NO
3
)
2
·2.5 H
2
O, silver nitrate, an alkali or alkaline earth metal chlorate or perchlorate, ammonium perchlorate, a nitrite of sodium, potassium, or silver, or a solid organic nitrate, nitrite, or amine, such as guanidine nitrate, nitroguanidine and 5-aminotetrazole, respectively. Preferably, the oxidizer comprises silver nitrate or a comelt or mixture comprising silver nitrate and at least one of an alkali metal nitrate, an alkaline earth metal nitrate, a complex salt nitrate, a dried, hydrated nitrate, an alkali metal chlorate, an alkali metal perchlorate, an alkaline earth metal chlorate, an alkaline earth metal perchlorate, ammonium perchlorate, sodium nitrite, potassium nitrite, silver nitrite, a complex salt nitrite, a solid organic nitrate, a solid organic nitrite, or a solid organic amine, and the metal fuel and oxidizer are present in amounts sufficient to provide an autoignition composition having an autoignition temperature of no more than about 232° C.
Typically, the autoignition temperature, the temperature at which the autoignition compositions of the invention spontaneously ignite or autoignite, is between about 80° C. and about 232° C. To obtain the desired autoignition temperature, the autoignition compositions of the invention may further comprise an alkali or alkaline earth chloride, fluoride, or bromide comelted with a nitrate, nitrite, chlorate, or perchlorate, such that the autoignition composition has a eutectic or peritectic in the range of about 80° C. to about 250° C. In addition, for compositions with low output energy, an output augmenting composition, which comprises an energetic oxidizer of ammonium perchlorate or an alkali metal chlorate, perchlorate or nitrate, in combination with a metal, may be added to the composition.
Preferred autoignition compositions include oxidizers of a comelt of silver nitrate and alkali metal or alkaline metal nitrates, nitrites, chlorates or perchlorates, or a nitrite of sodium, potassium, or silver, and mixtures of silver nitrate and solid organic nitrates, nitrites, or amines.
The powdered metals useful as fuel in the present invention include molybdenum, magnesium, calcium, strontium, barium, titanium, zirconium, vanadium, niobium, tantalum, chromium, tungsten, manganese, iron, cobalt, nickel, copper, zinc, cadmium, tin, antimony, bismu
Knowlton Gregory D.
Ludwig Christopher P.
Felton Aileen B.
Fitzpatrick ,Cella, Harper & Scinto
Talley Defense Systems, Inc.
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