Ca4PO42O

Ca4PO42O, commonly written Ca4(PO4)2O, is tetracalcium phosphate, an anhydrous calcium phosphate phase. It is a white to light-colored powder that is practically insoluble in water. TTCP is notable for its high calcium-to-phosphate ratio and its role as a reactive cementing phase in biomedical materials.

Its chemical composition corresponds to four calcium ions for two phosphate groups and one oxide ion, yielding a Ca/P ratio of 2. In aqueous environments TTCP is not stable; it slowly hydrolyzes to form hydroxyapatite, typically a calcium-deficient hydroxyapatite mixture that is more biologically compatible.

Synthesis: TTCP is produced by high-temperature solid-state reactions among calcium phosphate precursors, commonly CaHPO4 and CaCO3 or other calcium phosphate reagents, at temperatures around 1000–1300 °C, followed by milling to a fine powder. The phase is then handled as a reactive powder for cement formulations.

Applications: TTCP is a major component of calcium phosphate cements used in dentistry and orthopedics. When hydrated, TTCP reacts to form hydroxyapatite, enabling bonding to bone and tooth structures. In dental materials it is often combined with dicalcium phosphate dihydrate (DCPD) to form a setting hydroxyapatite matrix that mimics mineralized tissue.

Occurrence: TTCP is rarely found as a natural mineral and is chiefly produced for synthetic biomedical applications. It is valued for its conversion to biologically compatible calcium phosphate phases upon hydration.