2000 年 7 巻 286 号 p. 185-193
Hydroxyapatites (HAp) samples of various compositions (Ca/P molar ratio) and with or without trace metallic elements were synthesized by a precipitation method in Ca (OH) 2-H3PO4 system at various temperatures. Their morphologies and thermal stabilities have been investigated by using various analytical techniques, for example, XRD, TG-GC-MS, FT-IR, TEM. The precipitates were carbonate-containing HAp with small particle size. Thus a new index, Ca/ (P + C) was introduced instead of Ca/P. The HAp samples were from 1.62 to 1.73 for the Ca/ (P + C). Synthesized HAp decomposed to HAp and TCP for Ca/ (P + C) < 1.67 or to HAp and CaO for Ca/ (P + C) > 1.67 with heating above 630-850°C.
Further, specific surface area of standard HAp samples with trace metallic elements were larger than those of high purity HAp ones. This phenomenon was found to be due to the difference in pore volumes between the high purity and the standard HAp.
When the Ca/ (P + C) molar ratios increase, the unit cells become smaller. Thus it was suggested that vacancies at PO43- sites arise as the Ca/ (P + C) molar ratios become larger. It waas also suggested that a lattice water is substituted for OH- site for Ca/ (P + C) < 1.67 or PO43- site for Ca/ (P +C) > 1.67.