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Effect of the Crystal Size of Biogenic Hydroxyapatites on IR and Raman Spectra

This work focuses on the analysis of the impact that raw and calcined biogenic hydroxyapatite crystal size has on the Raman and infrared spectra. To this end, bovine, porcine, and human bones samples were defatted and deproteinized as well as calcinated at 720°C and then analyzed through Raman and Infrared spectroscopies, Transmission Electron Microscopy (TEM), Inductively Coupled Plasma (ICP), and Scanning Electron Microscopy (SEM). Raman and IR spectra for raw samples showed broad bands while after calcination bands became narrow and well defined. TEM images showed that all raw crystallites are nano-plates with a high crystalline quality contrary to the so far well-established concept that biogenic hydroxyapatites have low crystalline quality. This fact confirmed that the broad Raman and infrared bands of raw clean bones come from nanocrystal-plates. SEM analysis confirmed the increase in the size of the crystals after calcination from nano to sub-micron dimensions due to a coalescence phenomenon.