Table 1.
Main calcium phosphate phases, along with their chemical formulas, space group symmetries, solubility product values (Ksp) and solubilities at 25°C and pH 7.454,55,56,57,58.
| Phase | Chemical formula | Space group | pKsp | Solubility (mg/dm3) |
|---|---|---|---|---|
| MCPA* | Ca(H2PO4)2 | Triclinic P1̄ | 1.14 | 17 · 103 |
| MCPM* | Ca(H2PO4)2·H2O | Triclinic P1̄ | 1.14 | 18 · 103 |
| DCPD* | CaHPO4·2H2O | Monoclinic Ia | 6.6 | 88 |
| DCPA* | CaHPO4 | Triclinic P1̄ | 7.0 | 48 |
| β-CPP* | Ca2P2O7 | Tetragonal P41 | 18.5 | 7.6 |
| ACP* | Ca3(PO4)2·nH2O | / | 25 | 0.8 |
| α-TCP* | Ca3(PO4)2 | Monoclinic P21/a | 25.5 | 2.5 |
| β-TCP* | Ca3(PO4)2 | Rhombohedral R3cH | 29.5 | 0.5 |
| TTCP* | Ca4(PO4)2O | Monoclinic P21 | 37.5 | 0.7 |
| OAp* | Ca10(PO4)6O | Hexagonal P63/m | 69 | 8.7 |
| CDHAp* | Ca10−x(HPO4)x(PO4)6−x(OH)2−x (0 < x < 1) | Hexagonal P63/m | 85 | 9.4 |
| OCP* | Ca8H2(PO4)6·5H2O | Triclinic P1̄ | 97.4 | 8.1 |
| HAp* | Ca10(PO4)6(OH)2 | Hexagonal P63/m | 117.3 | 0.3 |
| FAp* | Ca10(PO4)6F2 | Hexagonal P63/m | 120 | 0.2 |
*
MCPA = monocalcium phosphate anhydrous; MCPM = monocalcium phosphate monohydrate; DCPD = dicalcium phosphate dihydrate, a.k.a. brushite; DCPA = dicalcium phosphate anhydrous, a.k.a. monetite; CPP = calcium pyrophosphate; ACP = amorphous calcium phosphate (data pertain to the phase obtainable at pH 9 – 11); TCP = tricalcium phosphate; TTCP = tetracalcium phosphate; OAp = oxyapatite; CDHAp = calcium-deficient hydroxyapatite; OCP = octacalcium phosphate; HAp = hydroxyapatite; FAp = fluoroapatite.