Abstract
Amorphous aluminosilicates and silicas are prepared according to an acid or an alkaline sol-gel synthesis procedure, starting respectively from tetraethylorthosilicate and Al(NO3)3 or aqueous silicate and aluminate solutions. The textural behavior of aluminosilicates (%Al between 10 and 60) and silicas upon the addition of formamide, dimethylformamide and ethylene glycol is derived from N2-adsorption data. Comparison with acid synthesized silicas shows that for both the acid and alkaline aluminosilicates mainly an enlargement of the pore volume takes place. The relative small variations in pore size observed (except for ethylene glycol in the acid synthesis) can not account for the pore volume increase. Dimethylformamide even tends to decrease the pore size. This indicates that addition of organics effectively prevents the collapse of smaller pores. As a function of the Al-content, this feature is most pronounced for gels characterised by the highest degree of condensation (25% Al in acid medium, around 30% Al in alkaline medium). The organic additives do not have a positive effect on the crackfree drying of aluminosilicates gel bodies, except for ethylene glycol. The influence of organic additives on surface charge is established by cation exchange capacity measurements.
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