Abstract
Adsorption of water is a one of important physicochemical properties of clays, and allophane has extremely high water adsorption capacity due to its high specific surface. The water vapor adsorption of two allophane samples with low and high Si/Al ratios (0.67: KyP; 0.99: KnP), under various relative humidities (RHs), decreased with preheating treatment up to 400°C for 2h. The decrease in water adsorption at monolayer level (RH=0.45) was greater for KnP sample than for KyP sample, whereas the decrease in water adsorption due to capillary condensation between allophane unit particles (RH=0.6) was greater for KyP sample. These indicate that allophane hollow spheric particles in KyP sample were directly connected each other with the preheating, but those in KnP sample were not. The difference in the way of bonding between unit particles in the two types of allophane was ascribed to the presence of polymerized silicate ‘tails’ exposed outside of hollow spheric allophane particles. In the KnP with higher Si/Al ratio, many ‘tails’ are exposed, and the ‘tails’ might prevented direct attachment between particles by forming connection between the ‘tails’. The presence of the ‘tails’ in allophane with higher Si/Al ratio was also related to dispersion property of allophane of this type.
