Yuanzineng kexue jishu (Jan 2024)
Oxygen Diffusion in Oxide Film and Matrix of Zirconium Alloys
Abstract
The diffusion coefficient of oxygen in zirconium alloy oxide film and matrix is an important parameter in corrosion kinetics of zirconium alloys. At present, there are some reports on the diffusion coefficient of oxygen in zirconium and oxide film, but the numerical values in the literature are quite different. In this paper, zirconium alloy was corroded in pure water to obtain a sample with an oxide film thickness of 1 μm. Through vacuum annealing test, the oxygen concentration distribution of the oxide film at four different temperatures was obtained, the diffusion coefficient of oxygen in zirconium alloy matrix was calculated, and the Arrhenius relation of the diffusion coefficient in this temperature range was obtained by fitting. Compared with the literature data, the trend is similar, but the values are different. The main reasons may be the following two aspects:One is the measurement deviation of oxygen concentration distribution curve, including spatial position deviation and concentration error, and the other is the different grain size of samples. The diffusion coefficient of oxygen in zirconium metal without irradiation obtained in this work can be mutually verified with the literature data, which has high reliability. Based on the corrosion weight gain curves of two zirconium alloys at four different temperatures, the diffusion coefficient of oxygen in the zirconium alloy oxide film was estimated by the equivalent diffusion model of the oxide film and the corrosion weight gain curve before the corrosion transition. It is found that the diffusion coefficient of oxygen in the zirconium alloy oxide film increases obviously with the increase of temperature, and the diffusion speed of atoms is significantly affected by the microstructure of the diffusion medium except temperature. Based on the research of two parts, it is found that the diffusion coefficient of oxygen in the oxide film is greater than that in zirconium metal when the temperature is below 440℃, and the diffusion coefficient of oxygen in the oxide film is more than twice that in zirconium metal when the temperature is below 400℃, which shows that the diffusion of oxygen in the oxide film of zirconium alloy is main at the interface at lower temperature (440℃ in this paper), and further shows that grain boundaries, pores and microcracks in the oxide film play a very important role in the corrosion behavior of the alloy. The above research provides important calculation parameters and basic research theory for the corrosion kinetic model of zirconium alloy. The results show that the diffusion coefficient of oxygen in Zr-Sn-Nb matrix follows a relationship as DZr(cm2/s)=0.18·exp(-180 000/RT). The diffusion coefficient of oxygen in oxide film, which follows a relationship as Dox(cm2/s)=3×10-7exp(-101 550/RT), is also evaluated by the weight gain profile in pre-transition stage.
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