The oxidation of zinc vapor in CO-CO2-N-2 gas mixtures

The kinetics of oxidation of zinc vapor in the Zn-CO-CO2-N-2 system was inv estigated for zinc partial pressures of 0.01 to 0.09 atm, carbon monoxide p artial pressures up to 0.5 atm, acid carbon dioxide partial pressures up to 0.6 atm at 730 degreesC to 900 degreesC. The experimental apparatus consis ted of a flow reactor and a multitemperature zone furnace. Known gas compos itions were generated and the rate of oxidation of zinc vapor was determine d from the mass of zinc oxide deposited under controlled conditions. The ra te of oxidation of zinc was found to be a function of temperature and of th e partial pressures of zinc, carbon monoxide, and carbon dioxide. It was au tocatalytic with respect to carbon monoxide and independent of the total ma ss of zinc oxide deposited, The reactions occurring in parallel for this me chanism are Zn (g) + CO2 (g) = ZnO (s) + CO (g) and Zn (g) + CO2 (g) + CO (g) = ZnO (s) + 2 CO (g) The two oxidation reactions occur simultaneously, both involving carbon dio xide and one with carbon monoxide as a catalyst. The autocatalysis of the reaction by carbon monoxide is explained by this m echanism, 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 ex pression). The experimental results fitted a rate expression of the form [GRAPHICS] 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 temperat ure. The term K-eq is the equilibrium constant for the reaction Zn (g) + CO2 (g) = ZnO (s) + CO (g).