Evaluation of water profiles at silica surfaces at 23°C, 100°C and 200°C by Zouine et al

The reaction equation for the reaction between water and silica reads
≡Si-O-Si≡ +H$_2$O ↔ [2 SiOH]
For this reaction the equilibrium constant, k, is affected by internal swelling stresses. We investigated the behaviour of erfc-shaped distributions of the total water amount in earlier Reports. The present report is intended to evaluate more complicated water profiles. Water concentrations at silica surfaces were measured by Zouine et al. Some of their data showed deviations from the expected erfc-shape. The associated datasets were used to demonstrate the procedure of determining the local equilibrium constant and the distributions of the hydroxyl and molecular water species on irregular water distributions. In an Appendix we discuss what could be the reason for the deviations in the distribution of the total water C$_w$ from the erfc-shape. The occurrence of back-diffusion after aging is assumed.