Temperature dependence of the concentration of silanol groups in silica precipitated from a hydrothermal solution

The physicochemical characteristics of amorphous silica precipitated from a hydrothermal solution are investigated. The specific surface of silica is determined by the Brunauer-Emmett-Teller method from the data on low-temperature nitrogen absorption. The limits of the total water content are estimated according to the thermogravimetric data. The temperature dependences of the concentration of surface and internal silanol groups in the range 200-1200 degrees C are determined by comparing the thermogravimetric data with the Zhuravlev physicochemical constants for the silica samples under consideration. A new type of amorphous silica with a considerable concentration of internal water is revealed. It is established that the mechanisms of the removal of surface and internal water differ from each other.