PHASE-TRANSITION POROSIMETRY AND SURFACE-AREA DETERMINATION

The method of computerized dilatometric Phase Transition Porosimetry (PTP), developed previously, is outlined in comparison with the method of "Thermoporometry" and critically reviewed. The present revised method takes into account extreme cases in which the sample contains relatively large and/or extremely small pores. To prevent supercooling in the former case, this method calls for repeated cooling. Because of the substantial amount of unfrozen pore water at low temperatures in the latter case, the revised data processing takes into account dilation of pore water as temperature is lowered below 0°C. PTP can measure the pore body size in the case of pores having pronounced irregularities consisting of enlargements and constrictions. Thus it gives a unique opportunity for realistic determination of surface area from pore size distribution in such porous materials. Whereas, as can be shown thermodynamically, mercury intrusion porosimetry (MP) is bound to overestimate surface area. To support these statements PTP, MP, and BET data on some samples are presented. © 1990.