Effects of metal ions on the morphology of calcium sulfate hemihydrate whiskers by hydrothermal method

Abstract

The effects of Na+, Mg2+, Al3+ and Fe3+ ion concentrations on the crystal morphology of calcium sulfate hemihydrate whiskers formed via a hydrothermal method have been studied. In the presence of Al3+ concentrations higher than 1×10–3 mol/L the whiskers were significantly shorter and thicker and the presence of Mg2+ and Fe3+ resulted in shorter whiskers. The presence of Na+ did not affect the morphology of the whiskers. Through elemental analysis, it was determined that Mg2+ and Al3+ were selectively adsorbed on the surfaces of the crystals, whereas Fe3+ underwent a hydrolysis reaction to form a brown precipitate which decreased the ion concentration in the solution. These results indicate that in raw materials used for the industrial preparation of calcium sulfate whiskers, Al3+ and Fe3+ should be removed and the Mg2+ concentration should be less than 8 × 10–3 mol/L in order to obtain pure whiskers with high aspect ratios.