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.

Graphical abstract

Keywords

metal ions / morphology / calcium sulfate hemihydrate whiskers / hydrothermal method / selective adsorption

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Higher Education Press and Springer-Verlag GmbH Germany