J. Schreckenbach

Preparation and Microstructure Characterization of Anodic Spark Deposited Barium Titanate Conversion Layers

Anodic spark deposition (ASD) is an advanced plasma-electrochemical coating process to prepare polycrystalline, ceramic-like conversion coatings on metal surfaces. As an example, polycrystalline barium titanate (BaTiO{sub 3}) phases have been prepared by the anodic conversion of metal substrate and the metal ions in the electrolyte. By a combination of various characterization techniques, the configuration of the coating was elucidated. On the metal substrate a thin ({approximately}50 nm) passivating amorphous film of titania (TiO{sub 2}) first forms, which subsequently changes to anatase and rutile structures. With increasing anodic potentials, a plasma-chemical conversion reaction starts, leading to the heterogeneous formation of BaTiO{sub 3} layers of 2{endash}10 {mu}m thickness. The results of this study lead to the formulation of a model describing a polycrystalline and inhomogeneous layer configuration. {copyright} {ital 1999 Materials Research Society.}

Conversion film formation on titanium anodes in acetonitrile at high voltages

Thin films are potentiodynamically generated on titanium in acetonitrile at high voltages. The influence of the cell voltage on composition and structure of the thin anodic conversion films is investigated. A heterogeneous composition of the anodic films is found. Electron diffraction patterns and XPS measurements show the presence of titanium nitride and titanium carbide. The film contains also amorphous and crystalline titanium oxides. The crystalline oxides are especially tetragonal anatase and rutile.

Microstructure study of amorphous vanadium oxide films

Abstract Conversion films of vanadium oxides are potentiodynamically generated on vanadium in acetate electrolyte systems at high voltages. The microstructure of the about 5 μm thin anodic films is investigated. X-ray diffraction and transmission electron microscopy indicate the films are complete amorphous. X-ray photoelectron spectroscopy (XPS) measurements show V 2p 3/2 binding energies of mixed valance vanadium sub oxides. Electron spin resonance (ESR) experiments on isolated films at 130 K point to paramagnetic V 4+ centers in a disordered octahedral oxygen surrounding.

Laser-damaging as a useful tool for materials characterization by Raman microscopy

The deliberate transformation of materials caused by laser radiation in Raman microscopy is used for a better deduction of structural information of a materials system. Investigation of transformed material allows the characterization of the molecular structure of the genuine material. A special advantage is the transformation of amorphous phases to crystalline structures by laser-induced oxidation. Also, the crystallization into different crystalline phases in order to obtain spectra that can be interpreted with more reliability will be possible. Titanium oxides formed tribochemically as reaction products in wear scars, tribologically stressed ADLC hard coatings or potentiodynamically produced Ti/Ca/P/O layers were modified by laser-induced crystallization or oxidation. Raman analysis of these materials provide results that cannot be deduced from the spectra of the untreated materials.

Characterization of modified glassy carbon films

The composition and structure of the thin conversion films at pre- and breakdown state are investigated. The breakdown leads to a modified structure and composition. Raman spectra of modified films show the formation of glassy carbon with a defined size of crystallites. A typical morphology characterized by a strong structured surface indicates this breakdown state. Electron diffraction patterns of the pre-breakdown state show the presence of titanium nitride, titanium carbide and titanium oxide.