Salt crystal purification by deliquescence/crystallization cycling

¹ Laboratoire Navier (umr 8205), Ecole des Ponts - 6-8 ave Blaise Pascal, 77455 Marne-la-Vallée Cedex 2, France, EU
² Van der Waals-Zeeman Instituut (WZI), Universiteit van Amsterdam - Science Park 904, 1098 XH Amsterdam, The Netherlands, EU

^a noushine.bonn@enpc.fr

Received: 27 March 2011
Accepted: 26 June 2011

Abstract

In this paper we show how by repetitive humidity cycling high-quality single crystals of salt (NaCl) can be obtained. The drying of droplets of saturated salt solution, leads to many individual microcrystallites that grow close to the contact line due to the “coffee stain effect”. Subsequent humidity cycling leads to the growth of a smaller number of crystals by expulsing impurities. This allows us to obtain only one single crystal instead of several dozens of crystallites in as little as three cycles. The reduction in the number of cycles needed to obtain a single crystal can even be improved by the combination of two effects; firstly the deliquescence/recrystallisation cycling and secondly by controlling the wetting properties of the substrate with grafted monolayer treatments.