In situ synthesis of hydrophobic calcium sulfate hemihydrate whiskers

A simple hydrothermal method was developed in this study to synthesize hydrophobic calcium sulfate hemihydrate whiskers in the presence of stearic acid. The morphology of the whiskers synthesized under different conditions was characterized by scanning electron microscopy, and their average aspect ratio was also estimated. The optimum synthesis conditions are determined as follows: the concentrations of Na₂SO₄ and CaCl₂ solution for preparing the precursor are 1.1 mol L⁻¹; the precursor content in the autoclave is 10 wt%; the hydrothermal reaction temperature is 150 °C; and the hydrothermal reaction time is 4 h, respectively. Glycol was used to promote the dispersion of stearic acid in the seriflux. The results show that the hydrophobic calcium sulfate hemihydrate whiskers can be obtained with stearic acid as surfactant, and their average aspect ratio can reach about 91. (paper)