Adsorption systems at temperatures below the freezing point of the adsorptive

Abstract

Isothermal adsorption studies and the measurement of dimensional changes below the bulk freezing point of the adsorbate indicate that substances adsorbed in porous solids are unable to freeze in situ. The difference between the vapour pressure or free energy of the unfrozen adsorbate and that of the bulk adsorptive outside of the porous system is resolved by a desorption process; the desorbed matter freezes outside of the system while the vapour pressure of the adsorbate remaining in the pores decreases through meniscus formation. Mechanical breakdown of the system occurs only then, when this process cannot be completed and an equilibrium state is not attained. This mechanism was found to be valid for porous silica glass, hydrated cement paste, bricks, and even for biological substances such as animal and plant tissue, and foodstuff. This understanding has led to the development of new methods for testing the durability of building materials, clarification of some problems of the BET surface area determination method and it suggests an explanation for the action of cryoprotective agents. I.

Liquid-solid phase transformation of potassium iodide aqueous solutions of different concentrations held inside a porous material

“…This value is identical to that determined by Brunet al [8] in the case of pure water. This result confirms that the layer which does not change in state is free of solute, and is in good agreement with Litvan's assertion [10].…”

Isotherms of Capillary Condensation Influenced by Formation of Adsorption Films

“…The isotherms obtained look like experimental ones [9][10][11]. It is remarkable that hysteresis of capillary condensation takes place even in absence of pore blocking and metastable states of wetting films.…”

Weathering by segregation ice growth in microcracks at sustained subzero temperatures: Verification from an experimental study using acoustic emissions

“…Whereas the 9 % volume expansion effect may dominate the breakdown of small saturated samples frozen rapidly and cyclically in the laboratory, progressive segregation ice growth in cracks during periods of sustained temperatures slightly below 0 "C may generally dominate the weathering of rocks in many field settings. This situation, which also arises in studies of the frost resistance of concrete (Litvan, 1978), calls for the development of more diverse freeze-thaw tests in which both processes can be distinguished and probed systematically. It also suggests that considerably more caution than is customary is in order when attempting to relate results from standard diurnal temperature cycling, such as specific temperature thresholds for effective frost weathering (e.g.…”