In-situ impedence spectroscopy study of electrical conductivity and ionic transport in thermally grown oxide scales on a commercial FeCrA1 alloy

In-situ impedance-spectroscopy measurements were performed at temperatures between 600 and 1,000 degrees C to investigate ionic transport in oxide scales formed on Kanthal AF alloy. The samples were pre-oxidized at 800, 900 and 1,000 degrees C in air. The impedance spectra of the oxide formed at 1,000 degrees C exhibited essentially one semicircle, whereas samples oxidized at lower temperatures showed an additional semicircle at high frequencies suggesting a more heterogeneous oxide. The ionic-transference number, derived by measuring the voltage across the oxide scale, indicates that the oxide is a predominant electronic conductor. Ionic diffusivity in the oxide scales formed at different pre-oxidizing temperatures was calculated, using the ionic-transference number. The ionic diffusivities obtained in this way are in reasonable agreement with literature data acquired by other methods. The oxide-formation temperature has a significant influence on the conductivity and ionic-transport properties of the oxide scale.