Chemical mechanism of the Zr+O-2->ZrO2 combustion synthesis reaction

The oxidation of Zr particles under a combustion regime is investigated by discussing separately the macrokinetic aspects (Fourier's law of heat transfer) and the microkinetic aspects (the kinetic laws describing chemical and phase transformations of a solid particle). A very simple model with a single reaction step and two different mechanisms (and different laws) is assumed to describe the microkinetics, while filtration of the gaseous reagent through the porous sample is neglected. The microkinetic variables (conversion degree and temperature) are then identified with the corresponding global variables, and the set of macrokinetic equations is finally solved by numerical methods. The approach is used to investigate how the chemical mechanism is affected by process parameters such as oxygen partial pressure, size of the reacting particles, and dilution degree. It is shown that experimental determinations (such as wave speed, thermal and composition profiles, and their dependence on process parameters) can be effectively used to clarify the chemical mechanism of the combustion. Improvements of the approach and extensions to multistep reactions are also discussed.