INFLUENCE OF ANNEALING TEMPERATURE ON RF MAGNETRON-SPUTTERED CALCIUM-PHOSPHATE COATINGS

The effect of different annealing temperatures on the characteristics of thin calcium phosphate coatings fabricated by radiofrequency magnet ron sputtering was stud led. Annealing of the as-sputtered films was n ecessary to change the amorphous coating to a crystalline coating. The films were annealed for 2 and 4 h at 400, 600, 800, 1000 and 1200 deg rees C under dry argon or argon and water vapour flow. After annealing , the structure and the chemical composition of these films were chara cterized with incident light microscopy, Rutherford backscattering spe ctrometry (RBS), X-ray diffraction (XRD), and Fourier transform infrar ed absorption spectrometry (FTIR). Incident light microscopy showed cr acks in the coatings annealed at a higher temperature than 400 degrees C. RBS revealed that the as-sputtered coatings had a high Ca/P ratio which decreased with increasing annealing temperature. After annealing at a temperature of 600 degrees C or more the XRD showed crystalline hydroxyapatite (HA) coatings. However, the second phase, present in th e coatings, changed from tetra-calcium phosphate to calcium oxide to b eta-tricalcium phosphate with increasing annealing temperature. FTIR m easurements showed the existence of OH- and PO- bonds in all coatings, although the PO- bonds varied for different annealed coatings, from t he PO- bonds due to HA to PO- bonds due to other calcium phosphates. F rom the results of this study we suggest that 600 degrees C is probabl y the best annealing temperature to obtain a better characterization a nd understanding of the coating.