Abstract
Oxidation of pure vanadium in 0.133 and 1.33 Pa of oxygen pressure has been investigated at 702∼1087 K by means of a thermoelectrobalance etc., the results of which have been compared with those of the preceding study in oxygen pressures of 13.3 and 133 Pa. Oxidation proceeded according to a parabolic rate law. The Arrhenius plot of the parabolic rate constants showed an obvious discontinuity at around 800 K. The overall activation energy of 104 kJ/mol was obtained for oxidation in the temperature range of 800∼1087 K. Except the pressure dependence of the parabolic rate constant, the present results were quite similar to the preceding ones. Pressure dependence was scarecely observed in the overall oxidation behavior at 800∼1087 K in 1.33∼133 Pa oxygen pressure. On the other hand, obvious pressure dependences were observed in parabolic rate constants at 800∼1087 K and at 702∼751 K in the oxygen pressure range of 0.133∼1.33 Pa and that of 0.133∼13.3 Pa, respectively. To clarify the causes of these behavior, the parabolic rate constants were separated into that for the oxide scale growth and that for the oxygen dissolution into the metal. The mechanisum of the observed pressure dependence for oxidation was discussed.
