Preparation Process for Fine Particles of Finely-Controlled Morphology using Emulsion as a Reaction Field

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W/O/W emulsion (emulsion liquid membrane) system, which has been used for separation and concentration of metal ions, was utilized for preparation of fine particles.1. Preparation of Spherical Fine Particles of Rare Earth OxalateRare earth ions were transported from the external water phase into the internal water phase through the membrane, and well-defined spherical oxalate particles of 200-600 nm in diameter were obtained for almost all rare earths, Ce-Yb and Y. A simulation for rare earth ion transport through the membrane phase revealed that the particle size was controlled by the quantity of oxalic acid in each water droplet and also by the distribution of rare earth ions into the droplets, and this was confirmed experimentally. The control of the particle size was feasible by control of the feed rare earth concentration and size of the internal water droplets.2. Preparation of Calcium Carbonate Fine ParticlesCa ions were transported into the internal water droplets containing ca … More rbonate ions, and calcium carbonate particles were obtained. When the W/O emulsion was demulsified by Freeze-thaw method, micrometer-sized vaterite particles of hollow structure were obtained. Thus, by using W/O/W emulsion system, size, morphology, and also crystal structure could be controlled. In the case where phosphate ions were fed into the internal droplets, calcium hydroxyapatite fine particles were obtained.3. Preparation of Composite Oxalate ParticlesWhen binary metal ions are fed into the external phase, fine structure of the particles is expected to be controlled by controlling the transport of the ions through the membrane phase. As case studies, Sr-Pb oxalate and Co or Ni ferrite particles were prepared. As the former case, Sr oxalate particles containing finely dispersed nanometer-sized Pb oxalate were obtained. As the latter case, acicular Fe oxalate particles containing Co or Ni oxalate located near the particle surface were obtained, and were calcined to give Co ferrite or Ni ferrite acicular particles. Less