The Oxidation Kinetics of Zirconium in the Temperature Range 400°–600°C

Abstract

The oxidation kinetics of zirconium were determined in the temperature range 400~176 at subatmospheric pressures for exposure times of 650 hr at 400~ to 160 hr at 600~ by a microbalance technique. From scale thickness measurements, it was shown that at temperatures between 500~176 the amount of oxygen in the metal varies from 14 to 23% of the total oxygen consumption respectively. Further both the oxidation kinetics and the oxygen distribution between the metal and the oxide were found to be independent of changes of oxygen pressure from 0.25 to 50 cm Hg. The kinetics were fitted to a parabolic rate relation after an initial deviation. In the parabolic range, oxidation behavior approximated to a model in which the oxidation rate was determined by oxygen diffusion in both the oxide and metal.

Thermal oxidation of amorphous Al0.44Zr0.56 alloys

“…2). These parabolic growth constants for the external growth of the am-(Zr,Al)-oxide layer on the am-Al 0.44 Zr 0.56 alloy are similar to the parabolic growth constants of k p Zr = 1.41 Â 10 À14 cm 2 s À1 and k p Zr = 4.69 Â 10 À14 cm 2 s À1 , as reported for oxide-layer growth on crystalline Zr at 500 and 550°C [47]; the parabolic growth constant as reported for the oxidation of crystalline Al at 500°C (at p O2 = 1 Â 10 4 Pa) is significantly lower: k p Al = 8.89 Â 10 À18 cm 2 s À1 [48]. 3 The parabolic oxidation rates are governed by the rate of oxygen diffusion through the thickening am-(Zr,Al)-oxide layer towards the oxide/alloy interface via the anion-"vacancy" exchange mechanism, as discussed above (for details, see Refs.…”

“…However, following Ostwald's rule of stages, the crystalline oxide phase 3 The parabolic growth constants were given in units of g 2 cm À4 s À1 in Refs. [47,48]. These data have been recalculated here in units of cm 2 s À1 by considering the densities of monoclinic ZrO 2 (5.73 g cm À3 ) [49] and c-Al 2 O 3 (3.69 g cm À3 ) [48], respectively.…”