FIBROUS GROWTH OF TRICALCIUM PHOSPHATE CERAMICS

Structural transformation and sintering processes of tricalcium phosph ate (TCP) ceramics prepared from defective hydroxyapatite (Ca9HPO4(PO4 )(5)OH) were studied by X-ray diffraction (XRD) and atomic force micro scopy (AFM). Starting powders with Ca/P ratio similar to 1.5 were obta ined by adding 0.5 l of 0.3 M H3PO4 solution to an equal volume of 0.4 5 M Ca(OH)(2). In the prepared ceramics, the onset temperature for tra nsformation of defective hydroxyapatite into TCP (witlokite) agrees wi th the onset temperature for sintering (800 degrees C). Sintering occu rs through the formation of a fibrous structure, which resembles biolo gical hard tissue. In the 1000-1200 degrees C range, these fibres coal esce into grains of up to 0.6 mu m in size with a fibrous-laminar morp hology. At the end of this sintering stage witlokite transforms into a lpha TCP. At about 1450 degrees C, partial decomposition of alpha TCP into Ca2P2O7 + Ca4P2O9 is observed. AFM observations suggest that Ca2P 2O7 is Segregated in the liquid state and increases the velocity of gr ain growth (up to 12 mu m).