Surface changes of plasma sprayed hydroxyapatite coatings before and after heat treatment

Plasma sprayed and heat treated hydroxyapatite (HA) coatings, produced from fine HA powder (38-75 mu m) under a spraying power of 45 kW (in short FCs) and coarse HA powder (75-106 mu m) under a spraying power of 35 kW, (in short CCs) have been investigated, especially in terms of their surface characteristics. The X-ray diffraction results show that most of amorphous and decomposed phases transform into crystalline HA and the crystallinities of coatings are improved. The surface morphology of the coatings has been examined by electron probe microanalyser and field emission scanning electron microscope. At high magnifications the as sprayed FCs, with new nanosize particles and a netlike aggregated lamellar texture are observed on the surface. After heat treatment at 650 degrees C, the nanograde particles of FCs have a tendency to grow and increase in quantity. While the netlike aggregation disperses into a uniform petal-like texture similar to a porous structure with a high surface roughness. Energy dispersive spectra show that these particles and netlike structure are primarily composed of calcium and phosphorous with adequate amount of oxygen and the Ca/P ratio is 1.75, i.e. exceeding that of pure HA.