The wet mechanochemical process (MC) and chemical precipitation (CP) used to prepare hydroxyapatite (HA) and tricalcium phosphate (TCP) nanoparticles proved to be successful. In mechanochemical treatment, water and ethanol were used as a solvent but the last one improved particles agglomeration and decreased HA formation. This effect was also observed when aging temperature was decreased in wet chemical precipitation. Introduction. Calcium phosphate based ceramics have proved to be attractive

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... terials for orthopaedic applications. Among these bioceramics, particular attention has been given to hydroxyapatite and tricalcium phosphate due to its bioactivity and biocompatibility. The search for materials similar to the main mineral component of bone led to the development of nanoparticles. Several methods were used to prepare hydroxyapatite and tricalcium phosphate, namely wet chemical precipitation and mechanochemical synthesis [1, 2] . This work consists on using these methods to prepare HA and TCP nanoparticles, and to characterize those particles in terms of their physico-chemical properties. Materials and Methods Mechanochemical synthesis. For experiment MC01, appropriate amounts of calcium hydrogen phosphate (CaHPO 4 .2H 2 O, Fluka) and calcium oxide (CaO, Riedel-de Haën) were mixed together in de-aerated (with N 2 ), deionised and distilled water in order to obtain Ca/P=1,67. Experiment MC02 differs on the used solvent, with ethanol (99,8% vol, AGA) and experiment MC03 Ca/P ratio was 1,5. The mixtures were mechanically activated in ball mill at 400 rpm and room temperature for 24 hours. An alternative experiment (MC04) was performed under mild stirring with a mechanical stirrer. Crystals were then aged for 24 hours at room temperature. Wet chemical precipitation. HA nanoparticles were prepared by wet precipitation under stirring, at room temperature and N 2 atmosphere. Orthophosphoric acid (H 3 PO 4 , Merck) was added to a solution of calcium hydroxide (Ca(OH) 2 , Merck) and lactic acid (CH 3 CH(OH)COOH, Aldrich) till Ca/P ratio was 1.67. When the solution was homogeneous, ammonium hydroxide (NH 4 OH, Merck) was added till pH = 10. Crystal growth was allowed for 24 hr at room temperature (CP01) and at 4ºC (CP02). The obtained suspensions were filtered, washed and centrifuged. Part of the material was resuspended in distilled water, while other was dried at 80ºC and sintered at 1100ºC for 1hr. Particles size distribution was obtained in the suspensions by light scattering tests (Coulter LS 230) performed using water as a diluting medium. Key Engineering Materials Vols. 240-242 (2003) pp. 555-558 online at http://www.scientific.net