Structural and surface characteristics of pure and low molecular weight oligomer-containing silica gels

Abstract

The molecular weight water soluble oligomers which can be included in inorganic gels during their precipitation affects greatly the surface and structural properties of these gels. The structural and phase changes of the pure and polyglycol 400 containing silica gels were studied by X-ray and differential thermal analysis. The intensity of the broad band, which may be correlated with the start of conversion from β to α quartz, decreased by inclusion of polyglycol 400 in silica gel. The inclusion led to retardation of the dehydroxylation of the gel. On thermal treatment marked variations in the surface area and pore volume were also observed. The effect of the replacement of hydroxyl groups from the surface of the pure and 10% polyglycol containing silica gels thermally treated at 110°C with different acid centers, namely F −, I −, SO 2- 4 ions, was discussed. The pure gel exhibited a higher ability to exchange with the previous ion centers than the 10% polyglycol containing silica gel. On the other hand, the latter has a higher tendency than the former for the rehydration process. In general, marked variation in nitrogen uptake whether in the mono or multilayer regions was observed due to the replacement of OH groups with different acid centers.