The Reaction of Zirconium with Carbon Dioxide and Carbon Monoxide at 850°C

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Abstract
An investigation has been made of the kinetics, the chemistry, and the solid‐state processes for the reaction of zirconium with carbon dioxide and carbon monoxide at 850 °C. In carbon dioxide at 10 cm Hg pressure, the kinetic curve showed an initial decreasing rate, an intermediate increasing rate, and a final decreasing rate. The ratio of carbon to oxygen uptake by zirconium in carbon dioxide was dependent on time and varied from 0.19 to 0.04 over a period 1–48 hr. Carbon produced in the early stages of reaction was incorporated into the oxide and led to formation of a needle‐like phase of a ternary lower oxide or a solid solution at the metal/oxide interface. Due to a high ratio of carbon to oxygen uptake in carbon monoxide, this phase developed to a distinct intermediate layer between the oxide scale and metal substrate. The kinetic curves in this gas exhibited a continuously decreasing oxidation rate; eventually breakaway occurred, possibly due to the presence of the secondary phase at the metal‐oxide interface. In the range of parabolic oxidation for both carbon dioxide and carbon monoxide, the rates were similar in magnitude to that found in oxygen. Comparison of oxygen gradients demonstrated that the extent of oxygen solution in the metal was the same for oxidation in these gases.

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