Hydrothermal formation and characterization of magnesium oxysulfate whiskers

Magnesium oxysulfate (5Mg(OH)2·MgSO4·3H2O) whiskers with a diameter of 0.2–1.0 μm and a length of 20–50 μm were synthesized via the hydrothermal treatment of the slurry formed by mixing the MgSO4 and NaOH solutions at room temperature. The composition, morphology, structure and thermal behavior of the hydrothermal products were examined with X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermo-gravimetric analysis (TGA) and chemical analysis. The experimental results indicated that the process parameters, such as the concentration of the reactant, the dispersion of the Mg(OH)2 slurry and the temperature in hydrothermal treatment should be controlled carefully to synthesis 5Mg(OH)2·MgSO4·3H2O whiskers and to avoid the formation of the sectorial or granular impurities. 5Mg(OH)2·MgSO4·3H2O whiskers were decomposed gradually and converted finally to MgO particles after being heated in air at temperature up to 1050 °C. Granular products formed if the heating temperature was above 320 °C.