Effect of cetyl pyridinium chloride additive on crystallization of gypsum in phosphoric and sulfuric acids medium

A basic study was carried out to understand effect of Cetyl Pyridinium Cloride (CPC) on calcium sulfate dihydrate (gypsum) crystallization. Induction time was measured under different supersaturation ratios ranging from 1.222 to 1.979. This is the time elapsed between the achievement of supersaturation and the appearance of a solid phase. The results show that, the induction time decreases exponentially with increasing the supersaturation ratio. In addition, the surface energy increases with CPC compared to the baseline (without CPC). Number of molecules required for formation of stable nucleus are calculated to be from 3 to 41 molecules depending on supersaturation ratios and presence of CPC. Interestingly, with addition of the CPC, the mean diameter of the crystals and the median increase. The growth rate was found dependent on the supersaturation with and without CPC. (C) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.