Sintering of High-Purity Nickel Oxide

The results of an investigation of densification and grain growth during the sintering of high-purity NiO in various atmospheres are presented. The sintering of NiO powders is divided into three stages. Grain growth during the third stage follows the empirical equation D ²= K t, where D is the average grain diameter, K a rate constant, t the sintering time. The activation energy of grain growth was found to be 55 kcal. per mole. The shrinkage and weight loss during the sintering process in vacuum were larger than in argon, air, and oxygen. Grain growth during sintering also differed with the sintering atmosphere. It was concluded that the sintering process is not explained reasonably by the theory of a semiconductor.