Preparation and characterization of magnesium hydroxide sulfate hydrate whiskers

Reaction of magnesium sulfate with aqueous ammonia in a hydrothermal condition (150-180 degreesC) produced a fibrous magnesium hydroxide sulfate hydrate (MHSH) with a composition corresponding to a stoichiometry of 4.34Mg(OH)(2). MgSO4. xH(2)O. Chemical composition analysis showed that the quantity of x was more likely to be 2 rather than the well-known 3. The MHSH whiskers were about 0.3-2 mum in diameter and 40-100 mum in length, with an aspect ratio no less than 100. Selected area electron diffraction (SAED) and X-ray diffraction patterns (XRD) showed the whiskers were well-crystallized with an orthorhombic structure. An interesting superlattice was observed from the ED patterns but this superstructure was unstable under the radiation of a high-energy electron beam especially under HREM conditions. Several techniques such as XRD, TEM, EDS, HREM, XPS, TGA-DTA, FTIR, etc, were used to characterize the structural features and thermal behavior of the experimental products. Our sample of fibrous MHSH was found to lose two hydration waters at about 330 degreesC, to further decompose at higher treatment temperature, and to transform finally into MgO near 1000 degreesC.