Abstract
α-Calcium sulfate hemihydrate (α-HH), a kind of advanced cementitious material, can be prepared from calcium sulfate dihydrate (DH) in electrolyte solutions. The kinetics of the DH−α-HH transformation in CaCl2 solutions was investigated to better understand and, hence, control the transformation process. The results showed that the DH−α-HH transformation is a nucleation–growth limited process, following a dispersive kinetic model. The α-HH nucleation and growth were both promoted significantly with the increment of CaCl2 concentration and temperature. This is due to the enlarged activation entropy change and supersaturation, which were caused by the decreasing water activity and increasing solubility product ratio (Ksp,DH/Ksp,HH), respectively. The rate of DH−α-HH transformation in aqueous solutions can be effectively controlled by regulating water activity and temperature.
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