Crystal growth in porous materials—II: Influence of crystal size on the crystallization pressure

Abstract

A thermodynamically consistent equation for the calculation of the pressure generated during crystal growth in porous materials is provided. The treatment makes use of an equation derived previously (paper I of this series) which is based on the chemical potentials of loaded and unloaded surfaces of confined crystals in porous materials. The influence of the crystal–solution interface on the chemical potentials is analyzed and a more general equation is derived that can be used to calculate the crystallization pressure considering both the degree of supersaturation of the solution and the effect of the curvature of the crystal–liquid interface. The present treatment is compared to other equations available in the literature and the different approaches are discussed in detail. It is shown that, for a given concentration of a pore solution, the crystallization pressure increases with crystal size. The equation is also applied to calculate equilibrium growth pressures assuming idealized pore geometries such as spherical and cylindrical pores with small entrances. It is shown that existing equations, e.g. Everett's equation [Trans. Faraday Soc. 57 (1961) 1541] can be derived as a special case from the more general treatment provided in this paper. The growth pressure of a crystal in a large pore increases with decreasing size of the pore entrance. Finally, a brief discussion on the particular problems of irregular pore geometries and highly anisotropic surface free energies of salts in porous building materials is provided.