Studies on the Oxygen Gradients in Oxidizing Metals

The oxidation of zirconium was studied in the temperature range 840°–1100°C. Film growth and oxygen solution processes were separated experimentally. Oxygen solution obeys diffusion kinetics and remains parabolic for sufficiently thick samples. Film growth does not obey normal rate laws; an exceedingly rapid initial rate is followed by a period of slower growth. The over‐all weight gain curve is explained in terms of the separate film growth and oxygen solution processes. At temperatures voids form in the oxide; they act as diffusion blocks and promote formation of a duplex layer. The mechanism of void formation is discussed in terms of a condensation of oxygen vacancies. The effect of orientation, pressure, surface preparation, and initiation temperature are discussed.