Synthesis of α-calcium sulfate hemihydrate submicron-rods in water/n-hexanol/CTAB reverse microemulsion

Submicron-sized α-calcium sulfate hemihydrate (α-HH) has a promising application in the clinical field. In a reverse microemulsion using n-hexanol as the oil phase, aqueous solution of H2SO4 and CaCl2 as the water phase, and cetyltrimethylammonium bromide (CTAB) as surfactant, α-HH was successfully synthesized in the shape of submicron-rod. α-HH precipitated directly from the microemulsion and either remained metastable or hydrated to calcium sulfate dihydrate (DH) depending on the temperature, H2SO4/CaCl2 molar ratio, and reaction time. The surfactant also played an important role and an increase in the mass ratio of CTAB/water lowered the temperature needed for α-HH precipitation. A higher ratio of CTAB/water and temperature of above 90 °C was a good option for pure α-HH synthesis. After a thorough examination of the synthesis conditions, a reverse microemulsion method was established for the synthesis of α-HH with submicron size.