Abstract
The surface area of allophane and imogolite which had been dried over P2O5 in vacuo or heated at various temperatures was determined by the ethylene glycol monoethyl ether (EGME) and nitrogen (N2) methods. The result was compared with that of montmorillonite.
A part of water adsorbed on allophane and imogolite could not be replaced by EGME, being different from water adsorbed on montmorillonite. Adsorbed water must be completely removed prior to the treatment with EGME for the determination of the surface area of allophane and imogolite. For this determination the P2O5 vacuum-drying of the sample was suitable but the oven-drying at 105°C was not suitable on account of the collapse of pores of these minerals. The pores collapsed by heating was, however, recovered by remoistening. Heating at 200 to 300°C increased, whereas heating at temperatures above 300 to 400°C decreased the EGME and N2 specific-surface-areas of allophane and imogolite. The former increase was ascribed to the removal of strongly adsorbed water from the minerals, and the latter decrease to a destruction of the structure of the minerals which would result in decrease in their porosity. Infrared analysis revealed that some Si-O-Al linkages in allophane and imogolite were destroyed by heating between 300 and 400°C.
