OXIDATION-KINETICS OF ZIRCALOY-2 BETWEEN 450-DEGREES-C AND 600-DEGREES-C IN OXIDIZING ATMOSPHERE

The oxidation kinetics of Zircaloy-2 have been studied in the temperat ure range 450-600 degrees C under the atmosphere of flowing Ar/5%H-2, CO2/1%CO, and CO2. Using the micro-balance technique, the weight chang e of the specimen has been measured as a function of time. The results showed that the oxidation kinetics of Zircaloy-2 obeyed the cubic rat e law rather than the parabolic one. The effect of oxygen partial pres sure on the rate constant was not found under the present experimental conditions. On the other hand, the activation energies of the oxidati on were 145, 171, and 188 kJ/mol for Ar/5%H-2, CO2/1%CO, and CO2 atmos pheres, respectively. It was shown from the X-ray diffractometry that the specimens oxidized under the conditions of this study consisted ma inly of monoclinic zirconia and, to a minor degree, of tetragonal one. It is suggested that the lateral cracks observed with scanning electr on microscopy (SEM) may cause the slow diffusion of oxygen in the oxid e phase. (C) 1998 Elsevier Science B.V. All rights reserved.