Dynamic behaviour and chemical mechanism in the self-propagating high-temperature reaction between Zr powders and oxygen gas

The self-propagating high-temperature reaction between zirconium powders an d oxygen gas has been investigated by computer simulated experiments using a one-dimensional model which accounts for (a) solid state diffusion in the oxide layer growing at the surface of each reacting zirconium grain and (b ) the gaseous flux of oxygen molecules towards the reacting grain. Two proc ess parameters-dilution with additional zirconia, and oxygen pressure in th e reaction environment-have been considered. The results show that the reac tion can propagate under steady conditions with constant wave velocity and maximum temperature or under various unsteady conditions. The main process parameter controlling the dynamic behaviour is the dilution degree, with ox ygen pressure playing a minor role. Diffusion through the product layer and pressure flux can both be found as the rate determining step under steady propagation conditions, while unsteady propagation is always under diffusio n control. Lowering oxygen pressure has a stabilizing effect on unsteady pr opagation.