Experimental Procedure for Determining Transport Properties of Oxide Scales

To determine the transport properties of oxide scales growing on an alloy, a laboratory apparatus was developed which allows plotting of characteristic V = f (i) curves and oxidation with an applied electric field. The apparatus and formalism used are described; it appears that such experimental procedures allow determination of the mean ionic transport number, ti; the conductivity values σ, σ_i, and σ,_e; and the effective charge, Z*, of the moving species in the oxide scale (A1₂O₃ in the present case).     

Determination of Transport Properties of Alumina Oxide Scale

By measuring the potential difference between the two interfaces of an alumina scale developed on a FeCrAl alloy, or by applying an electric field during its growth, values of t_i, σ_i, and σ_e along with their temperature dependence were determined. A residual potential, V₀, which was measured between the two oxide interfaces, is related to the oxygen chemical potential gradient on the scale. Alumina growth is controlled by oxygenion diffusion (by either V" or O"_i), and the transport properties are modified by the amount and distribution of impurities.