Gas-Generating Mixture

The invention relates to a gas-generating mixture of a fuel, an oxidizer, a catalyst and a coolant.

Gas-generating mixtures of the aforementioned type, also known as gas generator sets, are characterized in that they permit a high gas output (>14 mole/kg) on combustion. They are used for rocket and tubular weapon drive systems, as well as for inflatable air bag and rescue systems. Particularly in the civil sector thermomechanical insensitivity and non-toxicity of the starting mixtures, as well as a lack of toxicity in the resulting gases is sought. Many systems in use do not or only very inadequately fulfil these requirements.

The reaction of these fuels with the hitherto used catalysts and oxidizers leads to an unsatisfactory gas composition and/or to an inadequate burn-up behaviour. In addition, many reaction mixtures have such a high combustion temperature that, for air bag applications, the thermally sensitive bag materials are damaged.

In the case of a mixture having the aforementioned structure, the problem of the invention is to lower the combustion temperature and raise the burn-up rate.

These fundamentally contradictory requirements are fulfilled, according to the invention, in that the oxidizer is Cu(NO.sub.3).sub.2 *3Cu(OH).sub.2 and the catalyst comprises a metal or a metal alloy on a carrier.

As a result of the oxidizer provided according to the invention there is a cold and rapid combustion. The maximum pressure is reached within milliseconds, the gas temperature remaining below harmful limits. The hitherto necessary slag-forming constituents, which are required in known systems for binding pollutants, e.g. alkali oxides, can be avoided in the mixture according to the invention, so that a higher gas output can be obtained.

The catalyst used according to the invention is mainly used for pollutant gas reduction (CO and NO), the term "catalyst" being understood in the wider sense of an active reaction component, which can itself be reacted and acts in a reaction-controlling and/or reaction-accelerating manner. The carrier serves to provide the main component with a large specific surface and a clearly defined particle size distribution. A further characteristic of the carrier is by physical and/or chemical processes, in a specific phase of the reaction, to develop a cooling action, which extends beyond a purely capacitive cooling action. The carrier can also act as a promoter of the main component. Not only the metal catalyst, but also the oxidizer are thermally and mechanically stable and in particular are not hygroscopic.

The catalyst is preferably a pyrophoric metal or a pyrophoric alloy on a carrier which, after burn-up is left behind as a solid. It can be a silicate, preferably a schist or framework silicate.

Silver has proved eminently suitable as the metal. Particularly in the case of civil applications non-toxic starting compounds and non-toxic reaction products are required. These requirements are fulfilled by fuels with a high N content and a low C content. These include the known fuels TAGN (triaminoguanidine nitrate), NG (nitroguanidine), NTO (3-nitro-1,2,3-triazol-5-one) and GZT (diguanidinium-5,5'-azotetrazolate) characterized by a particularly high nitrogen content (DE 4 108 225). Thus, when the mixture according to the invention is used for rescue and air bag systems preferably TAGN, NG, NTO and in particular GZT are used.

A preferred mixture consists of GZT and Cu(NO.sub.3).sub.2 *3Cu(OH).sub.2 with a compensated oxygen balance and up to 30 wt. % catalyst.

The coolant can be wholly or partly formed from Fe.sub.2 O.sub.3, whose oxidative characteristics in the reaction mixture can be additionally used (DE 41 33 655, EP 0 536 525).

The figure shows the behavior of pressure after ignition in the experiment described in the example.

A mixture of consisting of GZT, pyrophoric Ag on a schist or framework silicate carrier as the catalyst and Cu(NO.sub.3).sub.2 *3Cu(OH).sub.2 as the oxidizer is prepared in a ratio of 22.05:20.0:57.95 wt. %. With respect to its ignition and combustion behaviour this formulation was experimentally tested in a ballistic bomb. The enclosed pressure behaviour diagram was obtained, which shows that the mixture has good ignition and combustion characteristics. With a loading density of 0.1 g/cm.sup.3 the maximum pressure is in the range 250 bar (25 MPa), which is reached after approximately 21 ms (t(pmax)=21 ms). The pressure increase time between 30 and 80% of the maximum pressure is t.sub.30-80 =4.35 ms.

The combustion temperature can be very accurately determined by thermodynamic calculation and is 2345K. For the same fuel GZT and compensated oxygen balance other oxidizers give higher combustion temperatures, e.g. 2501K for KNO.sub.3, 2850K for NH.sub.4 NO.sub.3 and 3248K for KClO.sub.3.