Water concentration and diffusivity in Silicates obtained by vacuum extraction

Abstract

Water concentration, Cw, and the mean effective diffusion coefficient of water, Dw, were measured by vacuum hot extraction coupled with mass spectrometer evolved gas analysis (VHE). The study includes silica, soda- and potassium-lime-silica, cordierite, and lamp bulb glasses of water concentrations between 0.017 and 0.17 mol H2O/l (122 and 1159 wt. ppm) as well as cordierite single crystals. Cw was obtained by integration of the VHE water degassing rate dQw/dt. For powdered samples (≈ 50 to 150 mg) of silica, soda-lime-silica and cordierite glass with water concentrations between 0.033 and 0.15 mol/1, VHE results well confirm IR spectroscopy within 5 to 15 % accuracy. Dw could be obtained by two methods: dQw/dt of powdered samples was measured during isothermal VHE experiments and dQw/dt fitted versus time with the appropriate diffusion models. Alternatively, powdered samples were pre-annealed in vacuum before measuring their residual water concentradon by VHE as described above. Cw was then analogously fitted versus the vacuum pre-annealing time. The applied methods and samples allowed the measuring of Dw within 10-9 and 10-13 cm2 s-1. Calculated values of Dw for soda-lime-silica glasses agree with literature data and values obtained by IR spectroscopy within a factor of 2 to 4.