Crystal growth in porous materials-I: The crystallization pressure of large crystals

A critical review of the existing literature on the pressure exerted by growing crystals in porous materials reveals that a number of different equations are in use. A derivation of an equation for the crystallization pressure based on the chemical potentials of the loaded and the unloaded faces of a growing crystal is provided. The equation obtained is compared to other equations available in the literature and the different approaches are discussed in detail. The treatment also includes the non-ideal behavior of the liquid phase using the ion interaction approach (Pitzer equations) which is well-established in solution thermodynamics. Incorporating the ion interaction equations in the crystallization pressure equation yields a quite simple expression that appears to be more convenient than previous treatments. The equation is applied to calculate crystallization pressures for supersaturated solutions of aqueous NaCl, NaNO3, Na2SO4, and MgSO4 including the various hydrated forms of these salts. Depending on the nature of the salt, neglecting the non-ideal behavior may cause considerable error in crystallization pressure calculations. Finally, it is emphasized that the basic assumption of non-uniform pressure is fundamental to understand the dynamics of crystallization pressure evolving in porous materials.