Freezing of the capillary liquid condensing in fine pores

Abstract

As a model of a fine pore in a porous body, the cylindrical model has hitherto been used by most investigators intentionally or tacitly. In this paper, a conical pore model is found to be more general and feasible for theoretical considerations of the phase transition of capillary condensate, accompanying a change of contact angle. A new concept such as an effective contact angle or a pore radius, depending on the amount adsorbed in conical pores, is defined completely in accordance with the capillary condensation theory. On considering the freezing process of capillary condensate, it is shown that the frozen layer generated initially in the meniscus region is thickened with temperature decrease. Using this scheme of freezing process, a theoretical formula is derived for the relation between temperature and the radius of curvature of the solid-liquid interface. On the basis of this theory, it is clear that the anomalous excess in apparent heat capacity of sorbate obtained experimentally by Morrison et al. or Antoniou is reasonably attributed to the melting of the solidified condensate in fine pores.