Mechanochemical Synthesis of Bioactive Material: Effect of Environmental Conditions on the Phase Transformation of Calcium Phosphates During Grinding

Abstract

The effect of environmental conditions on the crystalline transformation of metastable calcium phosphates during grinding was investigated using X-ray diffractometry and fourier transformed infrared spectroscopy. A mixture of CaO and dicalcium phosphate anhydrate (DCPA, CaHPO₄) did not transform after grinding in air. On the other hand, CaO and dicalcium phosphate dihydrate (DCPD, CaHPO₄ 2H₂O) were converted into a noncrystalline solid. Mixtures of DCPD and Ca(OH), transformed into low-crystallinity hydroxyapatite after grinding in air. When ground under N₂, a mixture of Ca(OH)₂ and DCPD did not transform into hydroxyapatite, whereas that of DCPD: Ca(OH)₂:CaCO₃ = 1:0.8:0.2 did. The results of X-ray diffraction of FT-IR spectra suggested that the presence of carbon dioxide in the grinding system was necessary for transformation from metastable calcium phosphates to hydroxyapatite.