Preparation and characterization of magnesium–calcium hydroxyapatites

Magnesium–calcium hydroxyapatite (MgCaHAP) solid solutions have been prepared by a wet method from aqueous solutions with different molar ratios, Mg/(Mg + Ca), ranging from 0 to 0.5. The MgCaHAP particles formed were characterized by XRD, FTIR, TEM, TCP, TG-DTA and gas adsorption techniques. The Mg/(Mg + Ca) ratios of the formed MgCaHAP particles were less than those of the starting solutions. With increasing Mg content, the particles became less crystalline and agglomerates of the fine crystals and finally the products were amorphous at Mg/(Mg + Ca)>0.31. The amount of irreversible adsorption of CO2 and CH3OH showed a minimum at a molar ratio (Mg + Ca)/P of ca. 1.56, less than the stoichiometric ratio of 1.67.