THERMAL-BEHAVIOR OF HYDROXYAPATITE INTENDED FOR MEDICAL APPLICATIONS

Four commercial hydroxyapatites (both natural and synthetic) were test ed to assess transformations of the chemical and crystalline structure following variation of temperature from 20 to 1600-degrees-C. The the rmal behaviour of hydroxyapatite is relevant for biomedical applicatio ns such as plasma spraying of metallic implants. Thermogravimetric ana lysis showed a weight loss from each hydroxyapatite specimen, due to a release of structural H2O molecules; all the specimens up to 1300-deg rees-C were made of crystalline hydroxyapatite, determined by X-ray di ffraction; at 1470-degrees-C they were made of both hydroxyapatite and calcium phosphate, but at 1570-degrees-C of calcium phosphate exclusi vely. The diffractograms of the hydroxyapatite coatings showed the sam e peaks as the original powders, so at the chosen plasma-spray procedu re level no new phases were formed. The peak height was nevertheless l ower in the plasma-sprayed hydroxyapatites for all interplanar spacing values, which indicated a lower degree of crystallinity, associated w ith a random structure derived from an alteration to the original crys talline network.