Titanium-oxide interface structures formed by degassing and anodization processes

Abstract

High-resolution electron microscopy was used to investigate two types of titanium-oxide interface structures. The first type was generated by thermal oxidation during the degassing process, which is one step in the process of porcelain-fused-to-metal systems. The thermal oxidation was performed for 1 min at a temperature of 1073 K in a porcelain furnace under a reduced pressure at 27 hPa. Columnar and granular rutile oxide formed on the titanium, and the surface oxide layer was almost 1 μ m thick. On an atomic scale, the crystal size of the rutile adjacent to the interface decreased about 10 nm. In addition, a very thin transitional layer 2–3 nm thick formed at the titanium-oxide interface. The crystal structure of the thin layer seemed to be the T{i}O phase with a NaCl-type structure. The interface between the hcp titanium and T{i}O phases was coherent through the close-packed planes ((0 0 0 2)hcp and (1 1 1)TiO). Partial coherency was observed at the interface between the T{i}O and T{i}O2 phases. The second type of titanium-oxide interface was generated by anodization on a screw-type titanium implant. The morphology of the surface suggested that the titanium implant had been treated by spark anodization. The surface oxide, which was estimated to be about 10 μ m thick, was a mixture of the anatase-type T{i}O2 phase and the amorphous phase. The crystal size of the anatase varied from less than 10 nm to more than 100 nm. A phosphate anion was concentrated in the amorphous phase. Between the surface oxide and the titanium base, macroscopic defects like cracks and voids were observed. Microscopic observation could not confirm the formation of a clear interface and lattice coherency between the titanium and oxide as a result of the degassing process.