Effect of Heating on Adsorption Behavior of Porous Glass

The effect of heat treatment and fluoridation of the surface on the adsorption of n ‐butane on porous glass was studied. The BET surface area, pore‐size distribution, and porosity were obtained from N 2 isotherms of samples successively heated at temperatures from 350° to 865°C. Deformation of the bulk structure began at 700°C. A cylindrical pore model inadequately correlated changes in specific surface, mean pore radius, and porosity. Surface heterogeneity was decreased to some extent by heat treatment at 865°C. Treatment of the surface with HF caused no significant change in the heat of adsorption from that of the untreated sample. Adsorption sites other than surface silanol groups are proposed to explain the results.