Oxidation characteristics of basal (0 0 0 2) plane and prism (1 1 2̄ 0) plane in HCP Zr

The oxidation characteristics of (0 0 0 2) basal plane and (1 1 2̄ 0) prismatic plane of an unalloyed Zr were investigated. From the Zr crystal bar, the specimen representing a single crystal was prepared to be coarse enough to have its grain be 4×4×1 mm3 in size. After identifying the crystallographic orientations and planes by X-ray diffraction (XRD), the samples were cut out in such a way as the cutting planes could correspond to the desired crystallographic planes. Oxidation tests were carried out in water at 360 °C. The oxidation rate of the (1 1 2̄ 0) prismatic plane was faster than that of the (0 0 0 2) basal plane. The analysis of oxide using the synchrotron XRD revealed that the oxide grown at the basal plane had the preferred (2 0 0) plane in mono-ZrO2, while the oxide at the prismatic plane grew at both the (2 0 0) and (0 0 2) planes of mono-ZrO2. In addition, the oxide layer that had formed at the basal plane having only one preferred growth plane exhibited a high fraction of columnar oxide and a relatively wide range of protective barrier layer. These results mean that the characteristics of the preferred planes of mono-ZrO2 play an important role on the oxidation rate of Zr single crystal.