In Situ Measurement of Electrical Behavior of Metal/Oxide System During Zirconium Oxidation at 850 °C

Abstract

Comprehension of oxidation processes under the influence of an external polarization is still a challenge, despites numerous past studied. In this study, thermogravimetric analysis technique coupled with in-situ application of an electric voltage was used to investigate oxidation of zirconium. First technical challenge was to modify thermobalance to integrate polarization equipment without perturbation of measurement and of oxidation behavior. Surprisingly, the oxidation rate was found to remain independent on the applied voltage, despite a large range of applied potential +/-200 Volts. Modeling of oxidation rates according to diffusion mechanism combined with investigation of polarization curves of the metal/oxide/electrode system have shown that a high electrical resistance appears at the oxide/electrode interface, even with addition of an intermediate gold layer. This resistance prevents from generating sufficient voltage drop through the oxide layer (>10 V), necessary to modify the kinetics. Nevertheless, meaningful electrochemical properties using analogy with solid oxide fuel cell have been observed, allowing to propose a comprehensive approach of oxidation phenomena under polarization.