PRINCIPLES OF CREATION OF SMOKELESS GAS GENERATING COMPOSITIONS FREE OF TOXIC COMBUSTION PRODUCTS

摘要

Modern propellants for automotive airbag inflators must answer on very wide set of requests. One of the main among them is a smokeless, that is the absence of condensed combustion products, therefore the formulation must be constructed basing on CHNO-substances only. Though while an accident the passenger does not spend much time inside the car generants try to minimize as soon as possible the concentration of toxic gases (NO, CO). Thus propellants must have the formulation close to stoichiometric one, that is O=2C+0.5H, but this necessary request is not enough yet because even while burning at high temperature (higher than 2500K) even stoichiometric formulation generates many CO and NO, and at too fast gas propulsion and fast cooling the thermodynamic equilibrium. Therefore the combustion temperature have not to be too high, preferably 2000 K. or so. Very strong requirements are for the chemical (thermal) stability - after two-weeks exposition at 110 C samples have not to change their properties. Such requirements are fare more strong than for rocket propellants, because an automotive may be kept at too increased temperatures within a rather long time. As far propellant must burn within 50-60 msec (at 200 atm), high combustion rates are required. Besides it, naturally, there are many other requirements (low hygroscopy, stability to rocking, low sensitivity to shock and friction etc.) for ensure the inflator reliability, requirements to decrease the cost, the toxicity, to increase the gas capacity, to minimize water amount in combustion products etc. Sure, it's impossible to satisfy all requirements (moreover, we are sure, some of them are not enough reasoned), anyway there is a task to find compositions that would be optimal in all properties complex and would satisfy requirements in competitiveness fight of producers. Today's formulations may be conditionally divided on three types. The first one - with condensed combustion products, e.g. these formulations contain metals in the oxidizer (nitrates, chlorates, perchlorates, oxides, peroxides). Metal azides are in this category too - their application in airbag inflators is prohibited now in many countries because of too high toxicity of azides. The second category of formulations contains organic oxidizers basing on nitromines or close substances.