Integrity and thermal decomposition of apatite in coatings influenced by underlying titanium during plasma spraying and post-heat-treatment.
The integrity and thermal decomposition of calcium apatite are influenced by the underlying titanium during plasma-spraying deposition, especially at the apatite/titanium interface. The destruction of apatite at the interface is governed by substrate temperature, titanium catalysis, and its reaction with titanium dioxide produced from oxidation of titanium in the plasma gas. The apatite in the outer layer of coatings is affected mainly by the substrate temperature and can keep its integrity with a suitable plasma-spraying procedure to minimize the increase of substrate temperature. The heat treatment of the coatings in vacuum results in the decomposition of apatite to alpha-tricalcium phosphate (alpha-TCP) and tetracalcium phosphate monoxide (TCPM) with the increase of intensity approaching the interface, which roughens the surface of the coatings. In the air-heat treatment, oxidation of titanium produces a thickened, dense rutile layer at the interface which prevents titanium atoms from diffusing into the coatings and inhibits the titanium-catalyzed decomposition of apatite. The apatite adjacent to the rutile layer reacts moderately with rutile to produce calcium titanate (CaTiO3), alpha- and beta-TCP, while the apatite in the outer layer, separated from the rutile layer, maintains its integrity without decomposition even in a prolonged air-heat treatment. The retention of apatite integrity leads to a decreased surface roughness of the coating.
Weng
J
J
Institute of Materials Science & Technology, Sichuan Union University, Chengdu, P.R. China.
Liu
X
X
Zhang
X
X
de Groot
K
K
D001672:Biocompatible Materials; D002130:Calcium Phosphates / Q000737:chemistry; D018360:Crystallography, X-Ray; D006358:Hot Temperature; D006882:Hydroxyapatites / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D013055:Spectrophotometry, Infrared; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry
D001672:Biocompatible Materials; D002130:Calcium Phosphates; D006882:Hydroxyapatites; D014025:Titanium