The effect of applied fields on crystallisation

Abstract

The thesis provides a background on crystallisation, the effects of applied fields and summarises the techniques used for characterisation and analysis. The study of applied magnetic fields was carried out on three crystallising systems (a) sucrose, (b) lactose and (c) cocoa butter. Both sucrose and lactose were crystallised from aqueous solutions in incubators at 50°C in applied magnetic fields and the resulting crystals compared to the those obtained under zero field conditions. The results for the sucrose study where the magnetic treatment was carried out under static, dynamic pumped and dynamic syphoned conditions domonstrated that changes in phase, crystallinity, morphology and microcrystallinity were a result of the applied magnetic fields and additional strongly bound water was found to be present within the sucrose crystals most likely to be sucrose hydrates. The resulting sucrose crystals were dependant on the type of field applied, the purity of the sucrose solution and the residence time within the applied field. The lactose study under static conditions provided similar results concluding that applied fields resulted in a more controlled crystallisation resulting in increased crystal size, increased crystallinity and changes in morphology. Crystallisation of cocoa butter from the melt, under normal production conditions in applied fields, resulted in changes in morphology and the time taken to reach optimum tempering which were dependant on the type of applied field and the residence time in the applied field.