ELECTROCHEMICAL METHOD FOR THE INVESTIGATION OF TRANSPORT-PROPERTIES OF ALUMINA SCALES FORMED BY OXIDATION .1. THEORY

An electrochemical method is applied to the study of the transport properties of alpha-alumina scales developed by oxidation of alumina-forming alloys. This technique consists in plotting the characteristic curves V versus I of the scale. In this paper, relationships between the transport properties (sigma(i), sigma(e), t(i), . . . ) of the scale and the variations of V with I are analysed and discussed. Information about the conductivity variation in the oxygen chemical potential gradient of the scale can be obtained from the slopes of V-I curves and from the evolution of such curves for different outer P(O2) imposed to the oxide. This method will be applied to alpha-alumina developed by oxidation of a beta-NiAl alloy in part II.