Oxidation mechanism of titanium nitride in oxygen

Despite the apparent complexity of the linear oxidation of titanium or titanium nitride resulting from the formation of a layered structure of the rutile scale formed, the uniqueness of the mechanism is proven. The limiting step appeared to be the predominant short-circuit diffusion of oxygen (E 44 kcal · mole^–1) through a rutile lamella of variable thickness growing at the nitride-oxide boundary and fracturing periodically to form a detached porous layer through which molecular oxygen can penetrate. The pressure dependence of the diffusion process in the case of the nitride was associated with the outward migration of nitrogen, while the undulations of the kinetics under certain conditions were caused by the growth of a sintered, recrystallized outer zone of oxide. The periodic exfoliation of the oxide was related to its poor adherence to the substrate, certainly due to the presence at the nitride-oxide interface of a thin gray film probably composed of intermediate phases between TiN_x (or Ti) and TiO₂.