The Preparation of Spherical Calcium Phosphate Fine Particles Using an Emulsion Liquid Membrane System

Calcium phosphate fine particles were prepared by using an emulsion liquid membrane (ELM, water-in-oil-in-water (W/O/W) emulsion) system, consisting of Span 83 (sorbitan sesquioleate) as surfactant and VA-10 (2-methyl-2-ethyl heptanoic acid) as extractant (cation carrier). Calcium ions were extracted from the external water phase and stripped into an internal water phase containing phosphate anions, to form calcium phosphate particles. The submicrometer-sized spherical calcium phosphate particles obtained were characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrophotometry and thermal analysis (TG-DTA). The characterization revealed that the fine particles obtained were calcium-deficient apatite in combination with various other calcium phosphate species. Decomposition from hydroxyapatite to β-TCP (whitlokite) occurred at 973 K, and thermal treatment above 1073 K produced a β-TCP and CaO composite. The freeze−thaw demulsification method yielded well-defined spherical particles of 0.5−20 μm (mostly smaller than 10 μm) in diameter; the shape and size of the internal water droplets is likely to influence the morphology of the formed particles.