The Ageing of Silica Gels Affected by Hydrothermal Treatment

Commercial silica gels of the pyrogenic and precipitated types were hydrothermally treated for 72 hours at temperatures between 90 °C and 210 °C in water of autogenous pressure. The samples were characterised by IR spectroscopy, water and nitrogen adsorption. Stability and sorption capacity run similarly. The more Q 4 (Si(OSi) 4 ) building units the framework of a silica gel contained, the lower was its sorption capacity. Sorption capacity increased with rising number of structural defects characterised by the presence of Q 3 (Si(OSi) 3 OH) and Q 2 (Si(OSi) 2 (OH) 2 ) groups. Simultaneously, the hydrothermal stability of the silica material dropped off.