Silicon diffusion in sol-gel derived isotopically enriched silica glasses

We performed silicon diffusion experiments with sol-gel derived isotopically enriched silica glasses at temperatures between 1050°C and 1300°C. The diffusion profiles were measured by means of time-of-flight secondary ion mass spectrometry. Samples annealed in closed silica ampoules under argon or dry air reveal enhanced Si diffusion compared to Si diffusion in fused silica. On the other hand, annealing in a large alumina tube under ¹⁸O₂ ambient yields Si and O diffusion coefficients which approach the results for thermally grown SiO₂. The enhanced Si diffusion in sol-gel derived glass is proposed to be due to water residues which lead to the formation of silanol SiOH groups.