Effect of the calcination temperature on the composition and microstructure of hydroxyapatite derived from human and animal bone

The present work focus the study of cortical bone samples of different origins (human and animal) subjected to different calcination temperatures (600, 900 and 1200 °C) with regard to their chemical and structural properties. For that, not only standard techniques such as thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy were used but also mercury intrusion porosimetry. The latter technique was applied to evaluate the effects of the temperature on the microstructure of the calcined samples regarding porosity and pore size distribution. Although marked alterations in structure and mineralogy of the bone samples on heating were detected, these alterations were similar for each specimen. At 600 °C the organic component was removed and a carbonate apatite was obtained. At 900 °C, carbonate was no longer detected and traces of CaO were found at 1200 °C. Crystallinity degree and crystallite size progressively increased with the calcination temperature, contrary to porosity that strongly decreased at elevated temperatures. In fact, relatively to the control samples, a significant increase in porosity was found in samples calcined at 600 °C (reaching values around 50%). At higher temperatures, a dramatic decrease was observed, reaching, at 1200 °C, values comparable to those of the non-calcined bon