CHEMICAL MECHANISM OF THE ZR-2-]ZRO2 COMBUSTION SYNTHESIS REACTION(O)

The oxidation of Zr particles under a combustion regime is investigate d by discussing separately the macrokinetic aspects (Fourier's law of heat transfer) and the microkinetic aspects (the kinetic laws describi ng chemical and phase transformations of a solid particle). A very sim ple model with a single reaction step and two different mechanisms (an d different laws) is assumed to describe the microkinetics, while filt ration of the gaseous reagent through the porous sample is neglected. The microkinetic variables (conversion degree and temperature) are the n identified with the corresponding global variables, and the set of m acrokinetic equations is finally solved by numerical methods. The appr oach is used to investigate how the chemical mechanism is affected by process parameters such as oxygen partial pressure, size of the reacti ng particles, and dilution degree. It is shown that experimental deter minations (such as wave speed, thermal and composition profiles, and t heir dependence on process parameters) can be effectively used to clar ify the chemical mechanism of the combustion. Improvements of the appr oach and extensions to multistep reactions are also discussed.