Moisture Sorption in Porous Materials: A best fit description from experimental data

Abstract: Information on pore geometry is very important in any study of the mechanical and physical behavior of porous materials. Unfortunately pores are not very accessible for direct measurements. Indirect methods have to be used which involve impregnation (sorption) experiments from which pressure and weight data can be "translated" to pore geometry by known physical relationships. In this context, analytical descriptions are important which can relate moisture condensation in pore structures to ambient vapor pressure. Such a description, the extended BET-relation, is presented in this paper. Contrary to the well-known original BET-relation (Brunauer, Emmett, Teller) the extended version applies at any vapor pressure. Examples illustrate the capacity of the extended BET-relation to describe experimental data very well - and at the same time produce the best possible estimates of pore physical parameters, the so-called BET-parameters: The heat property factor, C, and the pore surface, SBET (derived from the so-called uni-molecular moisture content uBET). A software ‘SORP07’ has been developed to handle any calculations made in the paper. For readers who have a special interest in the subject considered this software is available on request to the author. Keywords: Porous materials, moisture, adsorption, desorption, BET-parameters.