Flow and Diffusion Analysis on the Kinetics of Reduction of Fused Silica in Hydrogen

The kinetics of the reduction of fused silica in hydrogen is studied from the viewpoint of the water vapor generation. The water vapor content in exhaust hydrogen gas is monitored at temperatures ranging from 700 to 1200°C. A model of the flow and diffusion of water vapor generated at the inner surface of a fused-silica tube in a hydrogen atmosphere is assumed for estimating the water vapor content. Then the reduction reaction rate constants are determined by the best fit to the measured water vapor concentrations at various temperatures in the range. Arrhenius plots of the rate constants give the activation energy to be approximately 85 kcal/mol, independent of gas flow rates and tube diameters, indicating that the reduction rate is reaction-limited. It is worth noting that this study demonstrates the validity of this numerical flow and diffusion analysis method on water vapor generation.