Characterization of hydroxyapatite: Before and after plasma spraying

Hydroxyapatite (HA) powder was characterized before and after plasma spraying using infrared spectroscopy and thermoanalytical techniques. Structural changes were observed from the infrared spectra for the plasma-sprayed powder. These changes involved dehydroxylation and misoriented hydroxyl ions with different configurations. Dehydroxylation was accompanied by decreased intensities for the O-H stretching mode at 3571 cm-1 and the O-H librational mode at 633 cm-1. A broad infrared band near 3400 cm-1 that was observed after spraying was attributed to the misoriented hydroxyl ions. The combined results from thermoanalytical techniques indicated that adsorbed water evolved in three stages below 500 °C, and that the dehydroxylation of HA started as low as 700 °C. A weight gain of the plasma sprayed HA was observed above 500 °C in inert atmospheres. This result indicates a strong tendency of dehydroxylated HA to restore hydroxyls. The decrease in the decomposition temperature of HA after spraying was attributed to largely perturbed structures.