Abstract:
In this study we report on a continual change of Ca:P ratio in monocalcium phosphate monohydrate (MCPM) by increasing the amount of NaOH added in to the MCPM. The phase identification, chemical compositions, thermal analysis and micro-morphology of the chemically formed powders were characterised with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The Ca:P ratio is observed to gradually change from 1.0, which corresponds to dicalcium phosphate dehydrate – DCPD, to stoichiometric 1.67 of apatite. Depending on the attained Ca:P ratio in the powder synthesized in the aqueous solutions, subsequent calcination of these chemically formed powders leads to the formation of various single phasic calcium phosphates or biphasic compounds. It is proposed that the high solubility of MCPM results in fast dissolution and reprecipitation. A multi-step chemical reaction is proposed to elucidate the reaction sequence in the aqueous MCPM – NaOH systems.
