ANALYSIS OF POROUS TEXTURE BY MEANS OF WATER-VAPOR ADSORPTION-ISOTHERM WITH PARTICULAR ATTENTION TO LOWER LIMIT OF HYSTERESIS LOOP

The hysteresis loops of the adsorption isotherms of water vapor at 25°C have been examined on several porous adsorbents. The adsorbents used are five samples of porous silica gel pressed at different pressures, porous hematite, and porous titania. The lower closure point of the hysteresis loop for water vapor at 25°C was found to be situated at a relative pressure close to 0.27, which is lower than the relative pressure of the closure point (0.42) for nitrogen isotherm at 77 K. The pore radius at the closure point was found to be 0.9-1.1 nm for the water isotherm and 1.7 nm for the nitrogen isotherm. These radii are assumed to be the minimum pore radii determined from the capillary condensation of adsorptive. The water isotherm at 25°C gives more information on the porous texture than can be found by examination of the nitrogen isotherms at 77 K. The pore size distribution curves for the above adsorbents have been calculated from the isotherms of both water vapor and nitrogen gas. © 1993 Academic Press. All rights reserved.