Comparative analysis of solid state hydroxyapatite synthesis

ABSTRACT Hydroxyapatite is a calcium phosphate considered a biomaterial used in bone restorations, since it has characteristics similar to the mineral phase of bone tissue. Due to its many methods of production, the synthesis of hydroxyapatite powder has stimulated interest of academic research and industries, as the conditions of synthesis and reagents influence the structure, morphology and application of the desired final compound. This work aims to perform a comparative study on hydroxyapatite powder synthesis using equal reagents by two different methods: mechanochemical and calcination. The synthesis of hydroxyapatite was performed by solid state reaction using as precursors, calcium hydroxide and calcium monoacid phosphate in stoichiometric quantities. The characterizations were performed by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, dispersive energy spectroscopy, density, porosity and Vickers microhardness. X-ray diffractograms showed a single phase for the mechanochemical method and more than one phase for the calcination method, the phases were confirmed after refinement by the Rietveld method and the average crystallite size was calculated by the Scherrer equation. Raman spectroscopy showed bands of the vibrational modes of hydroxyapatite. The micrographs characterized the morphological differences in the samples due to different synthesis methods and the dispersive energy spectroscopy indicated the calcium/phosphorus ratios of the samples, classifying it as calcium phosphate-based ceramic. Measurements of sample densities and porosities were performed using the pycnometer method based on the Archimedes principle. The values found were satisfactory, since they are close to theoretical values found in the literature. Vickers microhardness measurements were obtained in the samples, in order to verify their mechanical properties. The methods employed proved to be effective in the production of hydroxyapatite powders.