ROLE OF OXYGEN-SUPPLY IN HIGH-TEMPERATURE GROWTH OF COMPACT OXIDE SCALE

High-temp. oxidn. of metals at low-O impinging fluxes and low values of O partial pressure were considered on the basis of the fundamental aspects of oxidn. kinetics.  The oxidn. kinetics of Cu to the monovalent oxide was studied under appropriate exptl. conditions using app. consisting of 2 solid-state electrochem. cells, both with Y2O3-stabilized ZrO2 as the solid electrolyte, coupled together.  The cells operated as O sensors and O pump, resp., in such a way that O was generated and monitored close to the surface of the oxidizing sample.  The results obtained on a Cu foil at 1113 K over the O pressure range 1 × 10-14 (highly purified Ar) to 1500 Pa show a linear growth of the oxide for exposures ≤2000 s.  This was tentatively explained by assuming the O supply to the sample surface to be the rate-limiting step, instead of the solid-state diffusion into the growing oxide.