Effect Of Alkali Ferrocyanides On Crystallisation Of Sodium Chloride

Abstract

Sodium chloride (NaCl) is one of the ubiquitous soluble salts in the environment and is responsible for weathering of building materials. The salt weathering is attributed to the stress developed from crystallisation of these salts in pores of the building materials, with supersaturation as the driving force. In the last years, researchers have successfully mitigated the damage associated with the crystallisa-tion of NaCl by the use of alkali-ferrocyanides (crystallisation inhibitors) in porous building materials. The observed mitigation of the damage has been attributed to lowering of the crystallisation pressure, possibly related to changes in the crystal habit and preferential crystallisation of the salt in the form of efflorescence instead of crypto-florescence. However, the effect of the inhibitor on the development of the so-called crystallisation pressure has not been studied in detail yet. In fact, direct measurement of this pressure is challenging and, until now, only a few experiments have been successful. In this research, an experimental setup has been developed to directly measure the crystallisation forces of NaCl and the effect of fer-rocyanide on these, while visualizing the crystallization process under a microscope. Some preliminary tests using this setup have been carried out: these consisted in monitoring force evolution from a drop of solution with and without the inhibitor confined between two glass plates.