Sodium, magnesium and carbonate-containing calcium phosphates: synthesis and investigation

The results of calcium phosphates formation in an aqueous solution of Сa2+-Mg2+-Na+-PO43--CO32--NO3– systems at different molar ratios of Сa2+:Mg2+:Na+:PO43-:CO32– = (10-х-y/2–z/2) : х : y : (6-z) : z, (x = 0.25, 0.5, 0.75; у = 0.25, 0.5, 0.75, 1.0; z = 0.5, 1.0) at a temperature of 25°С with subsequent heating at 600°С for 2 hours are presented. In the case of a system with molar ratios Сa2+:Mg2+:Na+:PO43-:CO32– = (10-х-y/2–z/2) : х : y : 5.5 : 0.5 for x = 0.25 regardless of the amount of sodium cations (y = 0.25–1.0), modified apatite-type calcium phosphates (hexagonal system, space group Р63/m) were obtained. For system at a fixed sodium content (y = 0.25), with an increase of magnesium amount (x = 0.5, 0.75), the formation of biphasic calcium phosphates (a mixture of phases based on β-Са3(РО4)2 – trigonal system, space group R-3c and Са10(РО4)6(ОН)2) was founded. An increase in the amount of carbonate in the initial solution to a molar ratio of PO43-:CO32-= 5 : 1 also led to the formation of biphasic calcium phosphates with different contents of main components ((47-65wt%) (β-Са3(РО4)2 + (53–35wt%) Са10(РО4)6(ОН)2) with an increase in the amount of sodium from y = 0.5 to 1.0. FTIR spectroscopy data confirmed the partial substitution of phosphate-anion by carbonate groups in the structure of apatite-type calcium phosphate. It was found that biphasic calcium phosphates containing a complex of trace elements are characterized by higher activity in a model solution than monophasic apatite-related carbonate-containing calcium phosphates of similar composition, and can be used in the future to restore bone tissue.