AN XPS AND SEMS STUDY OF SILICA SOL-GEL METAL-SUBSTRATE INTERACTION

Some applications of ceramic materials are difficult because of the ma rkedly differing lattice bonding characteristics of ceramic and metals . This 'affinity barrier' can be overcome by the modifying of structur e and composition in the interphase region. In our work the silica sub layer was deposited by the sol-gel method on metal implants prior to e lectrophoretical deposition of hydroxyapatite coatings to improve the oxidation resistance of the metal surface and the adhesion of apatite to metal during the annealing. The aim of this study is to determine c hanges in chemical state and structure of the coatings caused by therm al treatment for the better understanding of a relation between their composition and properties. Plates of titanium, WT 1-0, Fe-Cr-Ni stain less steel and of low-carbon steel were covered with silica layer by t he sol-gel method. The coating on low-carbon steel was produced by the deposition of silica sol-gel directly on the metal or, the silica-tit ania opacified porcelain enamel was obtained by electrophoresis. In th e case of direct deposition, below 400-degrees-C, an amorphous layer w as formed while at 800-900-degrees-C for only 2-4 min the dense, fine crystalline structure was obtained including small amount of silicates and iron scales. The silica-titania enamel was electrophoretically ap plied on low-carbon steel pre-coated with nickel. During annealing nic kel is alloyed with iron and decreases oxygen transport towards iron d ecreasing the rate of FeO formation. The silica from the enamel reacts with FeO producing a small amount of silicates. Titania partially pre cipitates at the metal boundary in the form of the needle-like crystal s of FeTiO3, growing from the steel surface into the enamel. When stai nless steel was annealed at 700-degrees-C in air, the surface oxide wa s enriched in chromium and manganese while the silica surface was enri ched in iron and manganese.