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Research Letters in Materials Science
Volume 2007 (2007), Article ID 71284, 4 pages
Research Letter

Synthesis of Hydroxyapatite by Interfacial Reaction in a Multiple Emulsion

Graduate School of Science and Technology, Niigata University, Ikarashi 2-8050, Niigata 950-2181, Japan

Received 11 July 2007; Accepted 10 October 2007

Academic Editor: Yiu-Wing Mai

Copyright © 2007 Isao Kimura. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Interfacial reaction in a multiple emulsion, which is one of methods for producing inorganic microspheres, was applied to synthesize hydroxyapatite. The multiple emulsion was a W/O/W emulsion, made of dipotassium hydrogen phosphate solution as an inner aqueous phase, benzene as an oil phase, and calcium nitrate solution as an outer aqueous phase. The reaction was carried out in the multiple emulsion for 24 hours at 323 K. The crystalline phase was varied with an initial pH of the inner aqueous phase, and single phase hydroxyapatite was synthesized at an initial pH of 12. The products were composed of porous microspheres of less than 3 μm in size. The microspheres were composed of nanospheres of less than 120 nm in size. By considering the mass balance, it was suggested that each nanosphere was formed in an inner aqueous phase droplet.