The role of the counter-ions present in syntheses on the thermal stabilization of strontium and/or calcium apatites

Abstract The goal of this work was to study the thermal stabilization of calcium apatites in which the Ca 2+ ions were substituted for Sr 2+ in increasing concentrations via ionic co-substitutions. Two distinct standard syntheses were proposed for comparative purposes: one using counter-ions that were not easily incorporated into the apatite structure (NH 4 + /NO 3 − ) and one using counter-ions that can be easily incorporated into the structure (Na + /Cl − ). After calcination, only the apatites synthesized in the presence of NH 4 + /NO 3 − presented phase transformation. In contrast, the apatites synthesized in the presence of Na + /Cl − formed a solid solution after calcination, with Na + , Ca 2+ , Sr 2+ and Cl − sharing the same apatite lattice. Wavelength dispersive X-ray fluorescence spectroscopy (WDXRF), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and temperature-programmed desorption (TPD) techniques showed that the counter-ions present during the syntheses that are associated with CO 3 2− play an important role in the thermal stabilization of the apatites.