Segregation of tin oxide in oxide layer of zircaloy-type alloys

Zircaloy-type alloys including 1.51 mass% and 0.23 mass% of tin were completely oxidized in 0.1 MPa steam at temperatures of 673 K and 873 K. The chemical composition near surface of the fine fragments of the oxidized specimen was measured by X-ray photoelectron spectroscopy. The appreciable enrichment of tin oxide SnO2 near surface of fine fragments was observed, and it was attributed to the segregation of tin oxide SnO2 at the grain boundaries of zirconium oxide. It was also concluded that tin oxide SnO2 was not dissolved in ZrO2 in the initial stage of oxidation at temperatures below 873 K, and that the solubility of SnO2 in ZrO2 at 1,173 K was larger than 0.23 mass%. The diffusion coefficient of tin in the monoclinic phase of ZrO2 at 1,173 K was evaluated to be in the order of magnitude of 10-19-10-18cm2/s. (author)