Abstract
The adsorption-desorption isotherm of water on mesoporous silicas with pore diameters of 3.8 nm was measured at 298 K using a gravitational method. Type V adsorption-desorption isotherm with significant hysteresis was obtained. Capillary condensation was initiated around 0.4 - 0.6 relative pressure and complete pore filling with water occurred near the saturated vapor pressure. The kinetics of water adsorption-desorption was also investigated. The relaxation rate of water uptake in the capillary condensation state was much smaller than that in the layer adsorption or pore filling state. However, he relaxation rate increased with increasing the amount of stepwise change in relative humidity. This result suggests that, in the capillary condensation state, water transport mechanism in mesopores should be different from simple diffusion. Similar trend could also be observed in the desorption process.
