C. Leygraf

Electrochemical impedance spectroscopy study of the passive oxide film on titanium for implant application

The surface oxide film on titanium and its long-term stability in biological environments play a decisive role for the biocompatibility of titanium implants. In this study, the passive oxide film formed on titanium and its natural growth in a phosphate buffered solution with and without an H2O2 addition have been investigated by electrochemical impedance spectroscopy (EIS) measurements over a period of several weeks. In the absence of H2O2, the impedance response indicated a stable thin oxide film on titanium. However, the introduction of H2O2 into the solution resulted in significant changes in the EIS-spectra, which varied with exposure time. The interpretation of results is based upon a two-layer model of the oxide film, consisting of a thin barrier-type inner layer and a porous outer layer. The H2O2 addition in the solution led to a significant decrease in corrosion resistance of titanium and also to a thickening of the porous outer layer. The observations may provide an explanation of the unexpected in vivo titanium oxide growth and ion incorporation into titanium implant oxide surfaces.

Variation of oxide films on titanium induced by osteoblast-like cell culture and the influence of an H2O2 pretreatment.

Variations of titanium oxide films induced by osteoblast-like cells in a rat calvaria culture system and the influence of an H2O2 pretreatment have been investigated by using X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy. For abraded titanium, the results revealed that phosphate and calcium ions may incorporate into the surface oxide film during the cell culture, forming a precipitate with a Ca/P ratio near that of hydroxyapatite. Oxidized carbon also was found in the surface layer, most likely precipitated hydroxylcarbonated apatite (HCA). The H2O2 pretreatment of titanium in a phosphate-buffered saline solution results in a 10-fold thickened porous oxide film and large amounts of surface hydroxyl groups as well as a certain amount of phosphate ions inside the oxide film. During the cell culture, the H2O2-treated titanium surface favors the ion incorporation and precipitation of the HCA-like compound, which probably is inlaid into the oxide film. Osteoblast-like cells on the H2O2-treated titanium showed a more active morphology during the initial stage compared with cells on abraded titanium. Moreover, bone-like nodule formation and mineralization appear to be related to the precipitation of the HCA-like compound on the surface. The results are discussed with respect to corrosion resistance, ion incorporation and precipitation of the HCA-like compound on the surface, osseointegration, and bioactivity of titanium implants.

Corrosion resistance for biomaterial applications of TiO2 films deposited on titanium and stainless steel by ion-beam-assisted sputtering

The high corrosion resistance and good biocompatibility of titanium and its alloys are due to a thin passive film that consists essentially of titanium dioxide. There is increasing evidence, however, that under certain conditions extensive titanium release may occur in vivo. An ion-beam-assisted sputtering deposition technique has been used to deposit thick and dense TiO2 films on titanium and stainless steel surfaces. In this study, using the following measurements these TiO2 films have been investigated in a phosphate-buffered saline solution: (1) open-circuit potential versus time of exposure, (2) electrochemical impedance spectroscopy, (3) potentiodynamic polarization, and (4) Mott-Schottky plot. A higher electrical film resistance, lower passive current density, and lower donor density (in the order of 10(15) cm-3) have been measured for the sputter-deposited oxide film on titanium in contrast to the naturally formed passive oxide film on titanium (donor density in the order of 10(20) cm-3). The improved corrosion protection of the sputter-deposited oxide film can be explained by a low defect concentration and, consequently, by a slow mass transport process across the film. As opposed to TiO2 on titanium, a deviation from normal n-type semiconducting Mott-Schottky behavior was observed for TiO2 on stainless steel.

Hydrogen peroxide toward enhanced oxide growth on titanium in PBS solution : blue coloration and clinical relevance

Oxide films formed on titanium exposed to a phosphate-buffered saline solution with and without hydrogen peroxide (H2O2) addition were investigated by means of electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). The oxide growth at the titanium/electrolyte interface was monitored in situ by daily EIS measurements during periods of several weeks. The results suggest that the oxide film can be described by a two-layer model with a barrier inner layer and a porous outer layer. H2O2 addition results in an increased dissolution/oxidation rate that leads to an enhanced oxide growth of the porous outer layer. As a result, the total oxide film can reach a thickness corresponding to an interference blue color. Based on XPS results, H2O2 addition furthermore seems to facilitate the incorporation of phosphate ions into the thicker porous layer. This observation may be related to the so-called osseointegration properties of titanium.

Eis and XPS study of surface modification of 316LVM stainless steel after passivation

Abstract The effects of surface finish, nitric acid passivation and ageing in air on corrosion resistance of 316LVM stainless steel in 0.5% H 2 SO 4 have been investigated by EIS, potentiodynamic polarization measurements and XPS. The results indicate that a smoother surface exhibits to a higher corrosion resistance. The effectiveness of the passivation treatment strongly depends on nitric acid concentration, passivation time and temperature. The passivation treatment significantly increases the corrosion resistance due to a high Cr content in the passive film and increased film thickness. Ageing after passivation increases the corrosion resistance whereas ageing before passivation has little effect.

Formation of NaZn4Cl(OH)6SO4.6H2O in a marine atmosphere

Abstract Recent investigations of zinc samples exposed in atmospheric field and laboratory exposure conditions have provided evidence of two newly discovered zinc chlorohydroxosulfates as corrosion products. In order to obtain a better understanding, detailed studies have been undertaken to characterize the formation and growth of both zinc chlorohydroxosulfates. One of them is observed mainly in marine environments, the other mainly in industrial environments, and the present study aims at describing the formation of sodium zinc chlorohydroxosulfate, NaZn 4 Cl(OH) 6 SO 4 · 6H 2 O, in a marine atmosphere. A field exposure program has been performed with emphasis on short exposure periods and detailed characterization of initially formed layers of corrosion products by means of a multianalytical approach. A reaction sequence is identified which is consistent with all methods used. It involves the consecutive formation of three structurally related phases, namely zinc hydroxycarbonate as the initial phase, zinc hydroxychloride as the intermediate phase and sodium zinc chlorohydroxosulfate as the final phase.

Investigation of interfacial capacitance of Pt, Ti and TiN coated electrodes by electrochemical impedance spectroscopy

Electrochemical processes at the electrode-electrolyte (body fluid) interface are of ultimate importance for stimulating/sensing electrode function. A high electrode surface area is desirable for safe stimulation through double-layer charging and discharging. Pt and Pt-Ir alloys have been the most common electrode materials. The use of TiN coating as the surface layer on the electrode has found increasing interest because of its metal-like conductivity, excellent mechanical and chemical properties, and the fact that it can be deposited with a high surface area. In this work, electrochemical impedance spectroscopy (EIS), which is a sensitive and non-destructive technique and widely used for characterization of electrical properties of electrode-electrolyte interfaces, was applied to investigate pure Pt and Ti, and TiN coated electrodes exposed to a phosphate-buffered-saline (PBS) solution. Platinized Pt and Ti were also studied for comparison. The capacitance value of the electrodes in PBS was obtained through quantitative analysis of the EIS spectra. The results reveal that the capacitance of the TiN coated electrodes with a rough surface is several hundreds times higher than that of a smooth Pt surface. Platinization of Ti can also increase the capacitance to the same extent as platina. EIS has been shown to be a powerful technique for characterization of stimulating/sensing electrodes.

Selective dissolution and surface enrichment of alloy components of passivated Fe18Cr and Fe18Cr3Mo single crystals

Abstract The possible surface enrichment of chromium and molybdenum during dissolution of Fe18Cr (110) and Fe18Cr3Mo (110) alloys at constant potentials in the passive region is elucidated by taking into account quantitative information on partial dissolution rates of alloy components as measured by γ-spectrometry and on chemical composition of passivating films as measured by ESCA and AES. Combining results from all methods it is found that chromium under all conditions is enriched in the passivating films. An accumulation of chromium in the alloy is also indicated. For molybdenum, an enrichment in the passive film is observed at − 0.2 V (SCE), whereas in the potential interval 0.1–0.9 V, the molybdenum enrichment as determined by ESCA and AES is hardly significant. On the other hand, γ-spectrometry gives a clear indication of molybdenum enrichment in both potential regions.

Seasonal variations in corrosion rate and runoff rate of copper roofs in an urban and a rural atmospheric environment

This paper summarizes the results from an extensive field exposure program implemented to study possible seasonal dependencies of copper corrosion rates and runoff rates. Two-year exposures in one ...

In‐Situ Raman Spectroscopy Combined with X‐Ray Photoelectron Spectroscopy and Nuclear Microanalysis for Studies of Anodic Corrosion Film Formation on Fe‐Cr Single Crystals

Detection et interpretation des spectres Raman des films passifs et transpassifs formes sur des monocristaux Fe-Cr en milieu 1M de KOH