Quantification of H2O speciation in silicate glasses and melts by IR spectroscopy -: In situ versus quench techniques

It is well established that near-infrared (NIR) combination bands at 4500 and 5200 cm(-1) can be used to measure the concentrations of OH groups and H2O molecules, respectively, in hydrous silicate glasses at room temperature. However, the variations of hydrous species concentrations and molar absorption coefficients for the combination bands with temperature in the glass and in the melt have been controversial in the past decade. Three different approaches are used to determine hydrous species at elevated temperatures: (i) long term isothermal heating nearby the glass transition terminated by a rapid quench, (ii) controlled cooling after heating the melt above the liquidus and (iii) in situ measurements. Each of these techniques has its advantage and disadvantage. In the case of highly polymerized alkali aluminosilicates, consistent data are obtained by the different approaches. Fictive temperatures of glasses, calculated on the basis of relaxation theory, are close to the equilibrium temperatures for the H2O speciation determined by in situ measurements. This indicates that the relaxation of hydrous species is coupled to relaxation of the silicate network.