NEUTRON-DIFFRACTION STUDY OF THE PORE SURFACE-LAYER OF VYCOR GLASS

Analysis of small-angle scattering and powder diffraction data combine d with macroscopic measurements have revealed the structure of a pore surface layer in Vycor glass, consisting of OH groups and chemisorbed water. Chemisorbed water exists on the pore surface in two forms: comp act water clusters of similar to 40-60 molecules, connected to each ot her by hydrogen bonds, and more spaciously distributed individual mole cules (or groups of several molecules). Heating to 650 degrees C recon structs the pore surface: the number of OH groups is significantly dec reasing due to the reaction of dehydration between Si-OH and B-OH surf ace groups. However, the temperature treatment does not affect the pro cess of H2O clusters formation, which still appear on the pore surface after the condensation.