The Porous Phase Barrier and Crystallization

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Abstract
A porous body can be used as a phase barrier, or to safely store or transmit a metastable fluid phase (B) under certain definable conditions even when a stable phase (A) outside the porous body is in intimate contact with the metastable phase inside the body. The condition to be met can be expressed by R < 2σV A [(S B -S A ) cos θ A δT] where R is effective (“cylindrical”) radius of the pores; δT is degrees of supercooling (or superheating); σ is specific surface free energy of the phase boundary; θ A is the contact anglen of Phase A with the material of the porous body; V and S are partial molal volume and entropy of the indicated phases, respectively. Phase B, the “metastable” phase by conventional test, is found to be the stable phase so long as it remains confined within sufficiently small pores. If the “metastable” phase (B) is a supercooled liquid, strongly adsorbed by the porous material (θ A > 90°), Phase A can be crystalline, as demonstrated by the natural process of frost heaving of soil. This implies new methods of managing crystallization processes, including one whereby saline water is purified by an “ice sandwich” that sustains reverse osmosis and another whereby components of a binary eutectic mixture may be completely separated.

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