Synthesis And Morphology Control Of α-calcium Sulfate Hemihydrate In A Reverse Microemulsion

a-Calcium sulfate hemihydrate (a-HH) is a very important class of cementitious materials and has multiple applications. The properties of a-HH are closely associated with the size, shape, and morphology, which is very important for its applications. Recently nano/submicron-sized a-HH has promising uses in the clinical field. Therefore, it is very important to explore an approach to synthesize nano/submicron-sized a-HH and develop a simple method to easily control the morphology on a large scale. In this paper, the reverse microemulsion method is employed for a-HH synthesis, focusing on the synthesis of nano/submicron-sized a-HH and the morphology control.For the first time, a-HH is successfully synthesized in a reverse microemulsion of water/n-hexanol/cetyltrimethylammonium bromide (CTAB). To clarify the conditions for a-HH synthesis, the effects of temperature, the crucial ingredient ratios, and reaction time have been investigated. a-HH precipitates directly from the microemulsion and its metastability strongly depends on the temperature,H2SO4/CaCl2 molar ratio and reaction time. The temperature required for a-HH synthesis decreases as the mass ratio of CTAB/water increases.In the above reverse microemulsion, the morphology of a-HH has been successfully controlled from nanogranule to submicrowhisker with tunable aspect ratio by only changing the mass ratio of CTAB/H2O and the concentration of sodium dodecylsulfonate (SDS). As the ratio of CTAB/H2O increases from 1.3 to 4.5, the crystal length decreases rapidly from 120-150μm to 0.5-1.0μm and the corresponding aspect ratio reduces sharply from 180-250 to 2-5. The crystal morphology gradually varies from submicro-sized long column to rod, hexagonal plate, and even nanogranule with an increase in SDS concentration. It is revealed that the preferentially adsorption of CTAB on the side faces and SDS on the top faces contributes to the efficient morphology control. The dissertation reveals that nano/submicron-sized a-HH can be successfully synthesized and the morphology can be freely controlled on a large scale in the water/n-hexanol/CTAB system. This work provides the basis for a-HH multiple applications and will offer great opportunities to explore its morphology-dependent properties and applications.