2000 Volume 22 Issue 1 Pages 1-10
The hydration enthalpies of three inorganic porous materials (sepiolite, MCM41 and synthesized allophane) were measured by means of the adiabatic vapor absorption calorimeter. The average hydration enthalpy (−ΔHh) were in the order, allophane (−57kJ/mol)<sepiolite (−54kJ/mol)<MCM41 (−49kJ/mol) when the samples were hydrated for 10 minutes in the calorimeter, after dehydration in vacuum at 100°C. Samples with smaller pore radius give the larger absolute values of the hydration enthalpy (−ΔHh). The −ΔHh values of sepiolite increased with dehydration temperature and decreased with hydration duration, whereas that of MCM41 remained almost constant regardless of dehydration temperature and hydration duration. The hydration rates for these samples were large in the early stage, but quickly lost the rate. The hydration state of the porous materials with large voids is concluded being similar to that of free water.