The oxidation of zinc vapor in CO-CO2-N2 gas mixtures

The kinetics of oxidation of zinc vapor in the Zn-CO-CO₂-N₂ system was investigated for zinc partial pressures of 0.01 to 0.09 atm, carbon monoxide partial pressures up to 0.5 atm, and carbon dioxide partial pressures up to 0.6 atm at 730 °C to 900 °C. The experimental apparatus consisted of a flow reactor and a multitemperature zone furnace. Known gas compositions were generated and the rate of oxidation of zinc vapor was determined from the mass of zinc oxide deposited under controlled conditions. The rate of oxidation of zinc was found to be a function of temperature and of the partial pressures of zinc, carbon monoxide, and carbon dioxide. It was autocatalytic with respect to carbon monoxide and independent of the total mass of zinc oxide deposited. The reactions occurring in parallel for this mechanism are and The two oxidation reactions occur simultaneously, both involving carbon dioxide and one with carbon monoxide as a catalyst. The autocatalysis of the reaction by carbon monoxide is explained by this mechanism, as is the observation that the effect of the partial pressure of carbon monoxide cannot be accounted for by a single p _CO term (the rate expression). The experimental results fitted a rate expression of the form over a wide range of conditions, with an accuracy of ±25 pct. Values of k ₁, k ₃, and k ₄ were calculated and expressed as a function of temperature. The term K _eq is the equilibrium constant for the reaction