Steam Oxidation of Zirconium–Yttrium Alloys from 500–1100^∘C

The steam oxidation kinetics, oxide formation, and hydrogen uptake of nuclear-grade Zr with 0.01–12 wt% yttrium were studied. Metallography and diffraction of the as-received material showed yttrium remained trapped in solid solution in concentrations up to 2 wt%; therefore, steam oxidation focused on 0.01–1 wt% Y samples. Thermogravimetric analysis was performed in a steam–argon environment at 500∘C,700∘C,900∘C, and 1100∘C at atmospheric pressure. At 500∘C and 700∘C, increasing the yttrium concentration increased the total weight gain by up to 300% and caused an increase the oxidation power-law exponent. At 900∘C, increasing the yttrium concentration caused a much smaller increase in the weight gain, and resulted in a decrease in the oxidation power-law exponent. At the highest temperature, 1100∘C, increasing the yttrium concentration had a minimal effect on the kinetics. Transmission synchrotron diffraction and cross-sectional optical microscopy showed significant hydrogen uptake at 500∘C and 700∘C through the formation of δ and γ zirconium hydrides. The volume of these two hydride phases increased with increasing yttrium concentration. This hydrogen uptake appears to be linked to the increase in the steam oxidation power-law exponent observed at 500∘C and 700∘C.