Microstructural characterizations of plasma sprayed hydroxyapatite coatings

The plasma sprayed hydroxyapatite (HA) coatings are used on metallic implants to improve their adhesion to bone. The coatings microstructure results from a rapid quenching of molten or partly molten particles that impact the surface at high velocity. The powder particles used to spray present coatings were prepared by spray drying technique and their sizes were determined using image analysis and laser sizers. The crystal sizes of initial powder and sprayed coatings were compared using Bragg peaks broadening method. The phase composition of coatings was analyzed by the use of room temperatures and high temperature (up to 900 °C) X-ray diffraction as well as by differential thermal analysis (DTA). The homogeneity of the deposits was evaluated using scanning electron microscope (SEM) and electron microprobe analysis (EMPA). The results suggest that the powder particles melt partially and the HA crystallites in coating are slightly greater than that of the powder. A small quantity of the decomposition phases was observed by EMPA and confirmed by DTA.