Abstract
Sector-like crystals of magnesium hydroxide sulfate hydrate (trade name MOS·HIGE) were grown in a hydrothermal reaction at 180°C using MgSO4 and NaOH aqueous solutions. Their morphology and crystal structure were investigated by X-ray diffraction, SEM and TEM. Typical morphology of the crystals was sector-like bundles, each of them grows three-dimensionally, not in a plane, in the opposite direction from its center. The element whiskers of the sector-like crystal were always parallel to the b-axis. In the initial stage of growth, a single crystallite composed of small whiskers growing along the b-axis nucleates in Mg(OH)2 slurry. During the growth of long whiskers from the crystallite, their growth direction slightly inclines with one another because of the lattice mismatching between two whiskers caused by impurities such as Na, Ca, Si and so forth on the boundary of an element whisker. Sector-like crystals were examined by the X-ray diffraction method at various high temperatures. It is found that they decompose into MgSO4 and MgO between 700°C and 1000°C. The diameter dependence of the tensile strength of the crystals was measured mainly at room temperature.
