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Some applications of ceramic materials are difficult because of the markedly differing lattice bonding characteristics of ceramic and metals. This 'affinity barrier' can be overcome by the modifying of structure and composition in the interphase region. In our work the silica sublayer was deposited by the sol-gel method on metal implants prior to electrophoretical 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 changes in chemical state and structure of the coatings caused by thermal treatment for the better understanding of a relation between their composition and properties. Plates of titanium, W T 1-0, Fe-Cr-Ni stainless steel and of low-carbon steel were covered with silica layer by the 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-titania opacified porcelain enamel was obtained by electrophoresis. In the case of direct deposition, below 400 "C, an amorphous layer was formed while at 800-900 "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 applied on low-carbon steel pre-coated with nickel. During annealing nickel is alloyed with iron and decreases oxygen transport towards iron decreasing the rate of FeO formation. The silica from the enamel reacts with FeO producing a small amount of silicates. Titania partially precipitates at the metal boundary in the form of the needle-like crystals of FeTiO,, growing from the steel surface into the enamel. When stainless steel was annealed at 700 "C in air, the surface oxide was enriched in chromium and manganese while the silica surface was enriched in iron and manganese. INTRODUCTIONCeramic materials are increasingly used in wear-resistant applications, owing to their excellent abrasion and corrosion properties. Several areas of advancing technology require high integrity for ceramic-metal interfaces but are difficult to produce because of the markedly differing lattice bonding characteristics of cermic and metals.'.' Thus the nature of the lattice bonding changes abruptly at ceramic-metal interfaces and it is important to understand how this is affected by the relative ionicity or covalency of the ceramics. This knowledge is important for the improving coating quality modifying both composition and manufacturing parameters.When a coating is deposited onto a substrate and fired to elevated temperature, interaction of the two systems is expected. This interaction may cause a change in physical or chemical properties of the ~o a t i n g .~ Reactions between a metal and oxide ceramics depend strongly on the activity of oxygen present in both the bonding atmosphere and the metal. It has been shown that the bond quality depends on the reactions and on the properties of the reaction products.Silica is known as an effective b...