Thermal treatment of Aerosil OX50: Pore structure and heats of immersion

Degussa Aerosil OX50 was thermally treated in vacuo, in the temperature range 20–1000°C. Effects of thermal treatment on the water contents, specific surface areas, pore structure and heats of immersion in water were investigated and discussed. Thermogravimetric analysis was used to select the temperatures of thermal treatment which reflect the various textural changes resulting from the heat effects. It could be shown that the heats of immersion in water depend on both the water content of the sample (molecular water and/or surface hydroxyls) and on the surface texture of the silica gel, that is, the pore structure. The interesting result obtained is that the heat of immersion in water is partly proportional to the mesopore fraction of the surface. Micropores lead to a decrease in the heat of immersion in water.