Oxidation of 0.4 wt%Ca-Be Alloy in Moist CO₂

Abstract

0.4 wt%Ca-Be alloy was oxidized in moist CO₂ (water vapour pressure, 14 to 25 mmHg) over the temperature range 700°∼800°C. Discontinuity of the weight gain vs. time curves suggests that the oxidation of 0.4 wt%Ca-Be alloy occurs through three reaction stages. The rates of oxidation at the initial two reaction stages were parabolic.
The effect of water vapour pressure on the parabolic rate constants as
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where k_p is the parabolic rate constant, k_p^° the parabolic rate constant in dry CO₂, a constant, ΔH the activation energy for the parabolic oxidation.
Pressure of moisture effected the activation energy of the reaction suggesting that the rate controlling step is different from that for dry CO₂. Increase in the partial pressure of water vapour causes a change in the entropy term in a manner indicated in the above equation.
The third stage follows a linear rate law resulting in a rapid disintegration.