REACTION OF HF WITH POROUS GLASS

Infrared spectra were used to follow the reaction of HF with porous glass which had been dehydroxylated to various degrees. The fluoridation proceeded smoothly, and the surface hydroxyls were eliminated completely with samples which were not degassed or were degassed mildly (at temperatures up to approximately 500°C) so that appreciable amounts of water and hydroxyls were on the surface before the HF treatment. Samples which had been severely dehydroxylated before exposure to HF behaved differently, and several HF treatments were required to effect complete fluoridation. Experiments suggest that the replacement of hydroxyls by fluoride is negligible at room temperature, the dominant reaction being the formation of B‐OH and B‐F groups. The latter are unstable at higher temperatures and release HF, so that dehydroxylation can continue after physically adsorbed HF has been desorbed and pumped away. Copyright © 1969, Wiley Blackwell. All rights reserved