Synthesis and Characterization of Mono- and Biphasic Ca1−xMnxHPO4·nH2O Compounds

Calcium phosphates and manganese phosphates play a significant role in biomedical and engineering applications, and these compounds are both synergistic. These compounds could have great potential for use in different applications, particularly as precursors of biomaterials. Therefore, the aim of this study was to explore the effect of the gradual replacement of Ca2+ with Mn2+ on the phase composition and crystal structure of brushite (CaHPO4·2H2O), which could be useful for the production of Mono- and Biphasic Ca1−xMnxHPO4·nH2O Compounds. In order to prepare the starting solutions required for this study, Ca(NO3)2·4H2O, (NH4)2·HPO4, and Mn(NO3)2·4H2O were used at various molar concentrations. Afterwards, the Ca1−xMnxHPO4·nH2O compounds were prepared using dissolution and precipitation methods. These compounds were characterized using XRD, SEM, FT-IR, XPS, and TGA techniques. The findings revealed that Mn substituted Ca partially at low Mn/Ca molar ratios, 0.25, and Mn doping increased the unit cell of CaHPO4·2H2O. The produced biphasic compound was composed of monoclinic CaHPO4·2H2O and nanostructured orthorhombic MnHPO4·(H2O)3 after a continuous increase in the Mn/Ca molar ratio to 1.5. When the Ca/Mn molar ratio was above 1.5, a monophasic compound of the MnHPO4·(H2O)3 phase was formed. The MnHPO4·(H2O)3 compound was successfully prepared for the first time using this dissolution-precipitation method. It was also established that the Mn/Ca ratio of the starting solution can be modified to produce CaHPO4·2H2O and MnHPO4·(H2O)3 phases with specific weight percent compositions.