SOLUBILITY CONTROL OF THIN CALCIUM-PHOSPHATE COATING WITH RAPID HEATING

The thin calcium-phosphate (Ca-P) coatings produced by the ion-beam-mi xing method instead of the plasma-spraying method have been found to b e amorphous, resulting in films that easily dissolved in simulated bod y fluid. These coatings crystalized with conventional heat treatment i n an electric furnace but tended to crack easily. Therefore, the purpo se of this study was to find a suitable heat treatment that controls t he solubility of Ca-P coatings without weakening their adhesion to tit anium (Ti) substrate. Thin coatings (approximately 1 mu m) were coated onto Ti substrates, followed by heat treatment in a conventional furn ace and rapid heating by infrared radiation and laser radiation. X-ray diffraction analysis revealed untreated films to be amorphous but to become crystalline after being heated in a furnace at 500 degrees C, h eated rapidly with infrared radiation higher than 600 degrees C and wi th laser radiation at output power of 10W. We evaluated solubility by estimating the film thickness after immersion in simulated body fluid for 5 weeks: Untreated films dissolved within 1 day. Coatings treated with infrared radiation at 600 degrees C dissolved minimally. Cracks w ere observed in coatings subjected to infrared radiation at 800 degree s C and furnace-heated at 500 degrees C. Coatings treated with laser r adiation tended to dissolve easily, with non-uniform surface degradati on. Xray photoelectron spectroscopy analysis at the interface between the coating and the Ti substrate showed that cracks were the result of decreased Ca-implanted layers and too much growth of Ti-P compounds. No difference was recognized in the Ti-oxidation state among specimens . These data indicate that rapid, homogeneous, and comparatively low-t emperature heating, such as defocused infrared radiation, controls Ca- P solubility and ensures the adherence of the coatings to the substrat e.