Explosive and thermic compositions or charges – Structure or arrangement of component or product – Solid particles dispersed in solid solution or matrix
Reexamination Certificate
1997-11-24
2001-05-08
Miller, Edward A. (Department: 3641)
Explosive and thermic compositions or charges
Structure or arrangement of component or product
Solid particles dispersed in solid solution or matrix
C149S019910, C149S036000, C149S046000, C149S047000
Reexamination Certificate
active
06228191
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a gas-generating preparation. In particular, the invention relates to a preparation comprising (a) ammonium nitrate, (b) a derivative of guanidine and (c) a deflagration catalyst which comprises one or more inorganic compounds, the preparation being able to produce a large amount of gas in a very short time. The invention further relates to the use of such a gas-generating preparation in an air bag.
For the purpose of the invention, an air bag is to be understood as a system comprising a sensor, a gas-generating preparation, an igniter for the gas-generating preparation and an inflatable reservoir in a folded state, which in the event of a dangerous situation can be inflated very quickly.
DESCRIPTION OF THE RELATED ART
Such a preparation is disclosed in U.S. Pat. No. 2,904,420. This preparation mainly comprises an oxidant, an organic combustible, an igniter and a cooling agent, the oxidant being an alkali metal nitrate or an ammonium nitrate, the organic combustible being guanidine nitrate or nitroguanidine, the igniter being copper in powdered form, a copper compound, a chromate compound or a polychromate compound, and the cooling agent being a naturally occurring magnesium carbonate such as magnesite or dolomite. The preparation contains from 15 to 40 wt % of the magnesium carbonate and—according to the examples—at most 34.2 wt % of ammonium nitrate. To prepare the preparations according to the U.S. Pat. No. 2,904,420 it may, owing to the addition of the cooling agent for reducing the burning rate, be necessary to choose such a quantity of the cooling agent that adequate cooling is obtained while still retaining a specific burning rate. It is also stated that the use of naturally occurring magnesium carbonate such as dolomite or magnesite in the gas-generating preparations is more effective than the use of magnesium carbonate or calcium carbonate which have been prepared by precipitation of these salts from solutions of magnesium salts or calcium salts in water.
A gas-generating preparation of this type is also disclosed by DE-A-195,505,569, which describes a preparation comprising a combustible, an oxidant, a deflagration catalyst and optionally an additive, the purpose of this additive being to diminish the formation of the amount of toxic substances. The combustible is a nitrogen-containing compound such as nitroguanidine or guanidine nitrate. The oxidant is a mixture of at least three peroxide, nitrate, chlorate and/or perchlorate compounds, one possible example of the nitrate compound being ammonium nitrate. The deflagration catalyst can be a metal carbonate, for example copper carbonate or iron carbonate. The preparation according to DE-A-19,505,569 preferably contains approximately 60 wt % of oxidants and up to approximately 8% of the deflagration catalyst.
A drawback of the gas-generating preparations according to the U.S. Pat. No. 2,904,420 and according to DE-A-19,505,569 is that these preparations are complex mixtures.
In addition, German utility model 9416112 describes gas-generating compositions which comprise at least (a) a carbonate, a hydrogen carbonate or a nitrate of guanidine, aminoguanidine, diaminoguanidine or triaminoguanidine, (b) an alkali metal nitrate or alkaline earth metal nitrate or ammonium nitrate and (c) a support material such as silicon dioxide, alkali metal silicates or alkaline earth metal silicates or aluminium silicates and/or an oxygen-supplying support material such as iron(III) oxide and copper(II) oxide. Also, instead of a carbonate, a hydrogen-carbonate or a nitrate of triaminoguanidine, it is possible to use nitroguanidine. The compositions can contain from 20 to 55 wt % of (a), from 45 to 80 wt % of (b) and from 5 to 45 wt %, based on the total amount of (a) and (b), of component (c). The compositions may optionally include a binder such as cellulose compounds or organic polymers.
Compositions such as those described in German utility model 9416112, in particular compositions which contain ammonium nitrate and triaminoguanidine nitrate or ammonium nitrate and nitroguanidine, proved to have the drawback that these compositions do not burn quickly enough and are not suitable, as such, for use in an air bag. A further drawback is that combustion of these compositions entails a too high burning temperature.
It was found that using certain metal carbonates as a deflagration catalyst both reduces the burning temperature and increases the burning rate of the composition. The invention therefore relates to a gas-generating preparation as noted above wherein the preparation comprises from 50 to 75 wt % of ammonium nitrate and the deflagration catalyst is copper(II) carbonate or iron(III) carbonate or a mixture thereof.
The metal carbonate is preferably iron(III) carbonate, copper(II) carbonate or a mixture thereof, in particular copper(II) carbonate.
Air bags are currently often used in cars. In the event of a collision the sensor will respond, whereupon an electric signal is transmitted to the igniter. The igniter ensures rapid decomposition of the gas-generating preparation with the formation of a large amount of gas by which the air bag is inflated very rapidly. In the event of the collision a person is then flung against the air bag which is in its inflated state. As a result, the person will not come into contact with any hard object in the car, for example the dashboard or the steering wheel, and the air bag consequently prevents the person from suffering serious injury.
The gas-generating preparation of an air bag according to the prior art is usually based on sodium azide. Such a preparation has two drawbacks. Firstly, the amount of heat generated is not sufficient for complete decomposition of the sodium azide. Secondly, sodium is formed as a by-product. The sodium reacts with humidity from the air and/or with moisture from the body, for example perspiration moisture, with the formation of sodium hydroxide which may lead to burns suffered by the person or persons present in the car.
Attempts have been made to overcome this problem by using, in an air bag, gas-generating preparations which, in addition to sodium azide, contain an oxidant, for example inorganic oxidants such as iron(III) oxide or copper(II) oxide or organic oxidants such as ammonium chloride, hydrazine chloride, hydroxylamine chloride and ammonium nitrate. In the process, the sodium formed in the decomposition of sodium azide is converted by the oxidant into sodium oxide. Albeit less violently, sodium oxide likewise reacts however, with humidity from the air and/or moisture from the body to give sodium hydroxide. These systems are not satisfactory, however, since the efficiency of gas formation is not optimal.
Use has also been made of gas-generating preparations containing sodium azide and metal halides, potassium perchlorate, metal powder and graphite, the objective being not to form any sodium or sodium oxide in the course of the decomposition of the gas-generating preparation. These gas-generating preparations have the drawback that their decomposition entails the formation of a large amount of solid particles. These particles, given the high temperature, often cause burns. Consequently, these particles need to be intercepted by means of a filter. The particles formed in the course of the decomposition are very small, however, and intercepting them by using an external filter proves difficult. Another drawback of the gas-generating preparations is that, since large quantities of solid particles are formed, the efficiency with which gas is formed is low.
Also known are gas-generating preparations based on sodium azide, which contain a so-called internal filter material. This filter material includes a low-melting material comprising metal oxides, which melts when the gas-generating preparation decomposes and is consequently able to capture the solid particles formed in the decomposition. This results in larger, tacky particles which can be intercepted more readily by means of an external filter. However, since
Miller Edward A.
Nederlandse Organisatie voor Toegepast-Natuurwetenschappelijk On
Young & Thompson
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