Hydrothermal synthesis of hydroxyapatite from natural source

Dicalcium phosphate dihydrate (DCPD) and anhydrous dicalcium phosphate (DCPA) extracted from a by-product in a manufacture of gelatin from bovine bone are used as starting materials for the hydrothermal synthesis of hydroxyapatite (HA) at temperatures of 160 and 200 degreesC under vapor pressures of 1 and 2 MPa, respectively. The suspension of DCPA with water gives a mixture of DCPA and HA as product but after adjusting the Ca/P molar ratio to 1.50 and 1.67 by addition of Ca(OH)(2), a single phase of HA with needle-like crystals is obtained. DCPA whiskers are produced in the suspension of DCPD with water but, on addition of Ca(OH)(2), the product obtained is again, a mixture of DCPA and HA. The coexistence of DCPA and HA is observed not only in the acidic region at pH 4.6 which is close to the known quasi-invariant point but also in the basic region at pH 12.3. Without addition of Ca(OH)(2) to the system, the complete conversion of DCPA or DCPD to HA is not possible. (C) 2002 Kluwer Academic Publishers.