Calcium orthophosphates

Abstract

The present overview is intended to point the readers’ attention to the important subject of calcium orthophosphates. This type of materials is of special significance for human beings, because they represent the inorganic part of major normal (bones, teeth and antlers) and pathological (i.e., those appearing due to various diseases) calcified tissues of mammals. For example, atherosclerosis results in blood vessel blockage caused by a solid composite of cholesterol with calcium orthophosphates, while dental caries and osteoporosis mean a partial decalcification of teeth and bones, respectively, that results in replacement of a less soluble and harder biological apatite by more soluble and softer calcium hydrogenphosphates. Therefore, the processes of both normal and pathological calcifications are just an in vivo crystallization of calcium orthophosphates. Similarly, dental caries and osteoporosis might be considered an in vivo dissolution of calcium orthophosphates. Thus, calcium orthophosphates hold a great significance for humankind, and in this paper, an overview on the current knowledge on this subject is provided.

Calcium phosphate coatings for marble conservation: Influence of ethanol and isopropanol addition to the precipitation medium on the coating microstructure and performance

“…Even with no ethanol addition, at pH 10 abundant formation of new phases occurred when marble was treated with a 0.1 M DAP and 0.1 mM CaCl2 solution, while no formation took place at pH 8 ( Figure 2). This is a consequence of the higher amount of PO4 3-ions originating from DAP dissociation at high pH [19]. However, because of excessive growth, the CaP coating is extensively cracked (Figure 6), which prevents effective acid protection.…”

“…An additional important effect of ethanol is the weakening effect it has on the hydration sphere of ions in the solution. In fact, DAP speciation in water leads to formation of PO4 3-, HPO4 2-, H2PO4 -ions, whose relative amount depends on the solution pH [3,19]. Each species in the solution is surrounded by water molecules, constituting the so-called hydration sphere.…”

“…Because a higher amount of PO4 3-ions (needed to form HAP) is expected to form from DAP dissociation in water at higher pH [19], the effect of increasing the pH of the DAP solution to 10 was investigated. In a previous study, we tried to increase the pH using NaOH [22], but the resulting coating exhibited limited acid resistance, likely because of the formation of soluble phases [22].…”

“…The idea is forming hydroxyapatite (HAP, Ca10(PO4)6(OH)2, the most stable CaP at pH > 4 [19]) by reacting marble with an aqueous solution of diammonium hydrogen phosphate (DAP, (NH4)2HPO4) [20,21], according to the reaction: 10CaCO3 + 5(NH4)2HPO4 → Ca10(PO4,CO3)6(OH,CO3)2 + 5(NH4)2CO3 + 3CO2 + 2H2O.…”

Magnesium incorporation into hydroxyapatite

“…Its composition differs from that of synthetic hydroxyapatite Ca 10 (PO 4 ) 6 (OH) 2 (HA), due to the presence of several ionic substitutions in the lattice, such as CO 3 2 , F , Mg 2+ and Na + . [1][2][3] These minor species not only alter the space group, morphology, stability, and mechanical properties of the HA structure, but also play an important role in the biological responses of bone cells. For instance, carbonates have a strong influence on the growth of apatite crystals, [1] sodium plays a role in bone remodeling, [4] whereas fluoride prevents the development of dental caries.…”