Abstract
Amorphous calcium phosphate (ACP), which generally forms as an unstable precursor during the initial stage of hydroxyapatite (HAp) synthesis, was synthesized by rapid dropwise addition of aqueous ammonia into calcium dihydrogenphosphate monohydrate (MCP) solution. ACP was crystallized easily to various calcium phosphates such as dicalcium phosphate dihydrate (DCPD), octacalcium phosphate (OCP) and HAp by dipping ACP (Ca/P atomic ratio 1.25-1.55) in various solutions. The present work was undertaken in order to elucidate the crystallizing conditions, composition and crystallographic data of a new phase formed by crystallizing ACP. The new phase was characterized by means of X-ray diffraction, thermal analysis (TG-DTA), infrared spectroscopy and scanning electron microscopy. The new phase was formed only by dipping ACP with a Ca/P atomic ratio above 1.40 in aqueous solution at 0°C for 24h. The results of chemical analysis and thermal analysis (TG-DTA) determined the chemical formula of the new phase to be Ca3(PO4)2⋅8H2O. Powder X-ray diffraction data did not correspond to those of already known calcium phosphates. Also, it was proved that crystallographic data of the new phase belongs to the monoclinic system with a=1.312nm, b=1.111nm, c=1.264nm, β=109.0°. Its crystal shape was plate-like 4-6μm across.
