Derivatograph was used to follow the modification of the skeleton structures of silica gels with alcohols and water vapour. Analogous investigations were carried out by other independent methods. Agreement between the results is good.The derivatograph is widely used at present in studies on adsorbents [1 -5] and packings of chromatographic columns [6,7]. Simon [1] described the applicability of the derivatograph for determination of the adsorption capacity of industrial adsorbents. Das et al. [3] recently used the complex method for studies on the change of amorphous silica into crystobalite.Utsugi et al. [4,5] have investigated the surface groups of silica gels chemically modified with alcohols by means of differential thermal analysis and thermogravimetry. Silica gels esterified with alcohols are used in chromatographyand in industry. Esterification reactions of hydroxylated silica gels with alcohols R-OH can be presented in a simplified way [9]:Si-OH + R-OH ~_ Si-OR + H20(1)The degree of esterification of the silica gel surface depends on the temperature and time of the reaction, the pressure of alcohol vapour, the water content of the reaction system, and the porosity of the modified xerogel [8][9][10]. Studies have shown that during reaction (1), in addition to changes in the adsorption properties of the silica gel [4,11 ], its texture and skeleton structure may also undergo modification [9,12].In the present paper the derivatograph has been used to follow the modification of the skeleton structure of hydroxylated silica gel with alcohols and water vapour.
ExperimentalFor the experiments we used adsorbents obtained by autoclave modification of the hydroxylated silica gel surface with n-alcohols and water vapour. Hydroxylated silica gel was produced by POCh Gliwice (Poland) and additionally purified with HC1. The reactions of the alcohols and water vapour with this silica gel were carried out in an autoclave. The following substances were used as modifying 2*