Interaction of water diffusion and hydrogen diffusion in silica glass at high temperatures

Both water diffusion and hydrogen diffusion in silica glass at high temperatures involve molecular diffusion and reaction with the glass network. One of the reaction products, hydroxyl, is common in both reactions and, therefore, the effective diffusion co-efficients of the two molecular species may not be independent of each other when both molecular species co-exist. The extent of the interaction was investigated by determining the effective diffusion co-efficients of water and hydrogen from hydroxyl profiles in a silica glass, prepared by melting in a hydrogen atmosphere, after heat-treatment at 750 °C in a wet atmosphere. In this case, water diffuses into the glass while hydrogen diffuses out of the glass. These diffusion co-efficients were compared with values obtained in the absence of other diffusing species: water without hydrogen and hydrogen without water. It was found that the effective hydrogen diffusion co-efficient was reduced by more than an order of magnitude by the presence of water vapor, while the effective water diffusion co-efficient was unaffected, within experimental error, by the presence of hydrogen.