Infrared spectral investigation of plasma spray coated hydroxyapatite

Plasma spray coated hydroxyapatite was studied using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Special attention was made to illustrate in terms of the infrared spectra the effect of spray distance on the coating, and the difference between the surface and the bulk of the coating. The difference in spray distance was not found to change the infrared band locations. However, band broadening was observed due to the lower crystallinity in the coating. One notable difference that was observed between the spectra of the surface and the bulk of the coating was the higher degree of splitting of the asymmetric P–O stretching vibration mode (ν3) from the coating surface. This difference was attributed to the perturbed environment around PO43− ions, and to the dehydroxylation and/or the misplacement of hydroxyl ions in the crystalline network that occurred for the apatite crystals during the plasma spray process.