Gas phase nitridation of silicate fiber glass materials with ammonia:Three case studies

Three types of the leached fiber glass materials of silicate origin modified with Zr, Al and rare earth metals (REM) were nitridated with ammonia at temperatures ranging from 673 to 973 K. DRIFTS (Diffuse Reflectance Infrared Fourier-Transform Spectroscopy) and H/D exchange using ND3 were applied for characterization of the formed NHx species. Along with nitridation of silanol groups their dehydroxilation as well as hydrolysis of NHx species take place. In situ DRIFTS study showed that the limiting steps are slow chemical reactions, but not a diffusion of NH3 or H2O molecules in the bulk of glasses. The concept on strained siloxane bridges formed due to dehydroxylation of two adjacent silanol groups was used for explanation of the reaction kinetics features.