Role of oxygen supply in high-temperature growth of compact oxide scale

Abstract

High-temperature oxidation of metals at low oxygen impinging fluxes and low values of oxygen partial pressure were considered on the basis of the fundamental aspects of oxidation kinetics. To do this, the oxidation kinetics of copper to the monovalent oxide was studied under appropriate experimental conditions using apparatus consisting of two solid-state electrochemical cells, both with yttria stabilized zirconia as the solid electrolyte, coupled together. The cells operated as oxygen sensor and oxygen pump, respectively, in such a way that oxygen gas was generated and monitored very close to the surface of the oxidizing sample. The results obtained on copper foil at 1113 K over the oxygen pressure range 1 × 10⁻¹⁴ (highly purified argon) to 1500 Pa show a linear growth of the oxide for exposures up to 2000sec. This was tentatively explained by assuming the oxygen supply to the sample surface to be the rate limiting step, instead of the solid state diffusion into the growing oxide.