Influence of preheating rate on kinetics of high-temperature gas-solid reactions

The influence of preheating rate on kinetics of high-temperature reactions in gas - solid systems was investigated by a computer-assisted electrotherm ography technique. Two systems were investigated: Nb -N-2 and Ti -N-2, in t he temperature ranges 2,100 - 2,500 K and 1,350-1,600 K, respectively. The results showed that for both systems reaction kinetics are enhanced by incr easing the preheating rate to the desired reaction temperature.. Analysis o f the experimental data in the context of the sharp-interface model showed that the activation energy of the diffusion coefficient does not depend an heating rate, while the preexponential factor is affected. Additional exper iments suggest that non-isothermal preheating, even though of short duratio n, about 10 ms, influences chemical reactivity of the solid reactant by cha nging its specific surface area.