Crystallisation of nickel Sulphide by Non-isothermal Cooling

Abstract

The crystallization kinetics of stoichiometric nickel sulphide (NiS) have been investigated using non-isothermal cooling. DSC was used to characterize the crystallization process which was observed to be complex thus excluding direct methods of characterization. Indirect methods were therefore applied. The temperature dependence was characterized by measurement of the onset temperature of crystallization. As the high temperature form of NiS (u-NiS) is quenchable, the degree of conversion for a particular cooling rate was measured from the proportion of a-NiS stabilized at ambient temperatures. A transition in the cooling rate dependence of the crystallization process was observed from both onset temperature and degree of conversion measurement. The data were fitted to a nonisothermal form of the Avrami equation which indicated that the change in crystallization mechanism was from three dimension crystal growth to one dimensional crystal growth. Bulk nucleation was indicated in both cases.