Simulating porous oxide films on zirconium alloys

Abstract

This paper reports an attempt to simulate thick porous thermal oxide films on zirconium alloy specimens by successively applying layers of sol-gel zirconia to an initial thin oxide film. The intent was to aid in the interpretation of impedance spectra obtained from porous oxide films. To the extent that double-peaked Bode plots of phase angle, similar to those obtained from thermal oxides, were obtained in the impedance spectra the attempt was successful. However, the impedance spectra obtained on the simulated films were insensitive to the number of sol-gel layers. The film always appeared to be a double layer film, which was interpreted as the thermal oxide (produced during sintering the sol-gel oxide) under the sol-gel oxide. The impedance spectra were also insensitive to the nature of the porosity, which took the form of multiple high aspect ratio cracks in the simulated oxide films rather than the small pores observed in thermal oxide films. Accurate comparisons of oxide thicknesses by interferometry and impedance measurements with mercury contacts were rendered difficult by evidence for internal reflections (at the sol-gel/thermal oxide interface) in the former and incomplete contact problems in the latter.