THE EFFECTS OF SUPERCRITICAL DRYING ON THE PROPERTIES OF A MONTMORILLONITE EXPANDED WITH COLLOIDAL PARTICLES

A sample of (commercially available) bentonite can be easily expanded using silica-rich colloidal particles containing various amounts of Al2O3, TiO2 or ZrO2. Supercritical drying (SCD) with CO2 or dimethyl ether (DME) generates expanded solids with macroporosities more typical of aluminas and aluminosilicate gels than of pillared clays or zeolites. Surface area, pore volume and average pore sizes are greatly affected by the drying conditions and the observed differences have been attributed mainly to the immiscibility of residual water (in the expanded clay) with the fluid used during SCD. These materials are stable to 800-degrees-C and exhibit greater Bronsted type acidity than bentonites pillared with Al2O3 or ZrO2 clusters.