Effect of heat treatment on pulsed laser deposited amorphous calcium phosphate coatings

Abstract

Amorphous calcium phosphate coatings were produced by pulsed laser deposition from targets of nonstoichiometric hydroxyapatite (Ca/P = 1.70) at a low substrate temperature of 300 °C. They were heated in air at different temperatures: 300, 450, 525 and 650 °C. Chemical and structural analyses of these coatings were performed using X-ray diffraction (XRD), FTIR, and SEM. XRD analysis of the as-deposited and heated coatings revealed that their crystallinity improved as heat treatment temperature increased. The main phase was apatitic, with some β-tricalcium phosphate in the coatings heated at 525 and 600 °C. In the apatitic phase there was some carbonate substitution for phosphate and hydroxyl ions at 450 °C and almost solely for phosphate at 525 and 600 °C as identified by FTIR. This was accompanied by a higher hydroxyl content at 525 and 600 °C. At 450 °C a texture on the coating surface was observable by SEM that was attributable to a calcium hydroxide and calcite formation by XRD. These phases almost disappeared at 600 °C, probably due to a transformation into calcium oxide.