Ammonium carbonate Apatites

Figure 5.14. Relationship of the Fluorine Content of Hydroxyl-Fluor-Carbonate Apatites to Neutral Ammonium Citrate Solubility.

Other synthesis reactions include hydrothermal techniques, hydrolysis of other calcium phosphates (Monma and Kayima 1987) and sol-gel methods (Masuda et al. 1990). Hydrothermal synthesis is the second most common method and, in comparison to the wet chemical method, is able to produce well-crystallized, compositionally homogeneous apatite (Yoshimura and Suda 1994). In this process, a mixture of calcium carbonate and di-ammonium hydrogen phosphate is subjected to 12,000 psi and heated to 275°C (Roy and Linnehan 1974). A high crystallinity, carbonate substituted HAp is produced by this method. Calcium phosphates that have been hydrolysed to HAp include octacalcium phosphate (Graham and Brown 1996), tricalcium phosphate (Nakahira et al. 1999), and brushite (Monma and Kayima 1987, Fulmer and Brown 1998, Manjubala et al. 2001). The chemical formulas of these and other inorganic compounds are provided in Appendix 1. 

Slosarczyk et al. have used a wet method to obtain carbonated HAp powders [56, 57]. Calcium oxide (CaO), calcium nitrate, calcium tetrahydrate [Ca(N03)2-4H20] or calcium acetate [Ca(CH3COO)2-H20] were used as the calcium source. As the phosphorous source, phosphoric acid (H3PO4) or di-ammonium phosphate [(NH4)2HP04] were used. The molar ratio of Ca P was 1.67. Ammonium bicarbonate (NH4HCO3) or sodium bicarbonate (NaHCOs) were used as reactants to introduce groups. Biological apatites in natural bone, dentin, and enamel... 

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