X-ray diffraction and infrared spectroscopy data review analyses of the calcium phosphates

Abstract

The objective of this literature reviews is to report the various methods used in the synthesis of the calcium monophosphates and condensed phosphates compounds, such as the co-precipitation method, Boulle's process, solid-state reactions, hydrothermal synthesis, and thermal dehydration, and present the crystalline data of these salts as classified from the hexagonal to the triclinic system. For the monophosphates, the compounds with (PO4)3- groups crystallized in the hexagonal, rhombohedral, trigonal, orthorhombic, and monoclinic systems, against the compounds with (HPO4)2- and (H2PO4)-, which are crystallized in low symmetry systems (monoclinic, and triclinic). For the long polyphosphates chain (PO-3 )n, where the formula contains one (PO4)3- group, the compounds crystallized in the high possible symmetry (tetragonal systems); the compounds of a formula containing two, three, and four (PO4)3- groups are crystallized in the lower symmetry systems (monoclinic, and triclinic). In the anhydrous cyclotetraphosphates, the substitution of 2K+ by Ca2+ induced lowering symmetry from the tetragonal system in CaK2P4O12 to the triclinic system in Ca2P4O12. The calcium cyclohexaphosphates are all found to be hydrate compounds. With ammonium cations, the (NH4)6P6O18.1H2O crystallized in the orthorhombic system, as a highly symmetrical system found in this phosphate type. Besides, the study is extended to review the inferred characterization made particularly for anions, PO3- 3-4-in γ-Ca(PO3)2, PO4 in CaHPO4, P2O7 in 3-4-6-β-Ca2P2O7, P3O9 in MnCa2(P3O9)2, P4O12 in Ca2P4O12.1.5H2O2⋅3H2O and P6O18 in Ca2K2P6O18.6H2O.