Current Density-potential Curves Research Articles

Development of an In Situ Micro-Corrosion Cell for the Investigation of Pitting Corrosion on Austenitic and Ferritic Stainless Steels

In order to investigate the electrochemical pitting corrosion in more detail, a micro-corrosion cell was developed, allowing real-time in situ optical observations of steel surfaces in direct correlation with electrochemical measurement results. In this study, the austenitic 1.4301–X5CrNi18-10 and the ferritic 1.4016–X6Cr17 stainless steel grades were examined in electrolytes containing chloride ions. The micro-corrosion cell revealed a stable pitting corrosion of the ferritic 1.4016 and metastable pitting corrosion of the austenitic 1.4301. The pits were characterized by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM) in detail. A clear correlation between current peaks in the current density-potential curve and the growth of many small pits on the test surface was established and was identified as metastable pit growth. In general, the pitting corrosion potential increased as the diameter of the test surface decreased for both stainless steels. In contrast to the complex precipitates of 1.4301, chromium precipitates with a significantly higher amount was detected on the entire surface of the 1.4016. The corrosion initiation was identified at the interface between the precipitates and the base material for both stainless steels. By comparing both materials, the ferritic 1.4016 had a lower pitting corrosion potential than the austenitic 1.4301 under all test conditions.

Galvanic Deposition of Ir-Pt-Particle As Bifunctional Catalyst for Unitized Regenerative PEM Fuel Cell

On the road to climate neutrality, hydrogen is becoming increasingly important as an energy carrier. This increase in importance is clearly illustrated, for example, by the hydrogen strategy adopted by the European Union (EU) in summer 2020, which aims to transform the EU's energy system, which is predominantly based on fossil fuels, and its sectoral value chains into a climate-neutral, integrated energy system. Regeneratively produced hydrogen is the energy carrier of the future. It is suitable for energy supply and enables the desired sector integration between the industrial, transport, energy and building sectors. [1] In order to make hydrogen fuel efficiently usable as an energy carrier of the future, electrochemical technologies are needed for the production of regenerative hydrogen as well as the reconversion of hydrogen into electricity. One possibility is polymer electrolyte membrane (PEM) technology. With PEM electrolyser cells (PEMEL), hydrogen can be produced by splitting water with electricity. For the reconversion of the hydrogen into electricity, the PEM fuel cell (PEMFC) can be used. This recombines hydrogen with oxygen to form water (with the release of electricity and heat). For the conversion chain two separate systems are required. A combination of both technologies can be realized by means of the unitized regenerative PEM fuel cell UR-PEMFC with internal reaction reversal. [2] This approach places special demands on the design of the oxygen electrode and the catalysts used there, since the reactions at this electrode represent the limiting factor for the performance of the cell. While platinum is the most suitable catalyst at the hydrogen electrode in both electrolyzer and fuel cell operation, a distinction must be made between the operating modes at the oxygen electrode. In fuel cell mode, the oxygen reduction reaction ORR takes place at the oxygen electrode. Platinum is a suitable catalyst for this. When switching to electrolyzer mode, the oxygen formation reaction OER takes place, with iridium proving to be the best catalyst, especially with regard to long-term stability. Accordingly for the oxygen electrode of a UR-PEMFC a bifunctional catalytic layer must be used. The composite of appropriately structured electrode material (titanium) and bifunctional catalyst layer is called a bifunctional oxygen electrode BOE. [3]In this work, the electrodeposition of iridium-platinum alloy particles as a catalyst for a BOE was investigated. The deposition was first performed galvanostatically from electrolytes containing iridium and platinum ions in different concentration ratios. First, the influence of the electrolyte composition and the deposition parameters, such as current density and temperature, on the alloy composition was investigated. Electrolytes based on hexabromoiridate and diammineplatinum(II) nitrite were used to deposit alloys with iridium mass fractions between 40% and 60%, which corresponds to the typical composition from other publications, in which the catalyst particles are mixed in the slurry [3], [5], [6]. Current yields between 40% and 50% were determined for the production of closed layers. The alloy composition was characterized using X-ray fluorescence analysis and enegiedispersive X-ray spectroscopy. Examination of the surface morphology by scanning electron microscopy showed that no isolated particles could be produced on the titanium electrode by galvanostatic deposition. Rather, exposed areas are loaded with too much catalyst, while other surface sections could not be covered with catalyst material. However, a homogeneous distribution of the catalyst particles is crucial for increasing the cell conductivity. For this reason, the electrolyte composition found was used for pulse current experiments. The pulse times were varied between 10 and 50ms. The pulse pauses were chosen so that one pulse cycle lasts 100ms. The best results were obtained with a pulse time of 25ms and a puls current density of 40mA/cm². Particles with an iridium mass fraction of 45% were deposited homogeneously on the oxygen electrode. Assuming a Faraday efficiency of 40%, the theoretical catalyst loading is 0.5mg/cm². However, by reducing the number of pulse cycles, lower loadings are also possible. The catalytic properties of the electrode were first recorded in nitrogen-purged 0.5M H2SO4 by plotting current density-potential curves and cyclic voltammetry. Very good activity or low overvoltage with respect to the OER was observed. Measurements for the ORR in oxygen-purged H2SO4 are still pending. To gain insight into the performance of the prepared oxygen electrodes, the prepared MEAs with an electrode area of 25cm² will be investigated in a hydraulically pressed test system. Figure 1

Enhanced corrosion resistance of adhesive/galvanised steel interfaces by nanocrystalline ZnO thin film deposition and molecular adhesion promoting films

ABSTRACT In this study, nanocrystalline ZnO (NC ZnO) films are considered as interface layers for polymer/metal bonds consisting of hot-dip galvanised steel (HDG) and epoxy resin. NC ZnO films with a thickness of less than one micrometre were deposited on HDG through hydrothermal deposition from aqueous Zn nitrate/hexamethylenetetramine electrolytes. Furthermore, 3-aminopropylphosphonic acid (APPA) and 3-aminopropyltriethoxysilane (γ-APS) were considered for molecular adhesion-promoting layers. 90°-peel tests of water-saturated epoxy films confirm the improvement of bond strength under humid environments. Electrochemical properties of the thin film coatings analysed by current density potential curves indicate effective inhibition of oxygen reduction and metal alloy dissolution. Scanning Kelvin probe (SKP) measurements confirm that the corrosive delamination of the polymer from the metal substrate is significantly slowed down by the considered surface modifications. The combination of NC ZnO films with APPA as an adhesion promoting molecule showed the best performances.

Synthesis of biomass derived product from Ziziphus spina-christi and application for surface protection of metal under acidic environment- Performance evaluation and thermodynamic studies

The aqueous extract synthesized using the biomass, Ziziphus spina-christi, was applied to protect the surface of aluminium under acidic environment. The influence of extract concentration (0–0.14 mg/ml), contact time (2–8 h) and temperature (303.15–313.15 K) on the inhibition efficiency was studied. Langmuir isotherm fitted well to the experimental observations (R2 > 0.960) confirmed the monolayer attachment of inhibitors. The values of activation energy observed in this study suggests that the inhibition process to be surface interaction-based process. Thermodynamic parameters confirmed the process as feasible and exothermic. Potentiodynamic polarization and Electrochemical impedance spectroscopy studies are conducted to study the mechanism of corrosion. The electrochemical corrosion kinetics was studied using current density–potential curves and the Tafel constants (βa and βc) were calculated as 154.42 and 128.35 mV, at 0.14 mg/mL of inhibitor concentration. The biomass-based corrosion inhibitor was characterized using scanning electron microscope and attenuated total reflection techniques.

First-principles microkinetics simulations of electrochemical reduction of CO2 over Cu catalysts

Electrochemical reduction of CO2 can contribute to the storage of excess renewable electricity in chemical bonds. Here we incorporate reaction energetics for CO2 reduction on Cu(111) and Cu(211) determined by DFT calculations in microkinetics simulations to predict the influence of surface topology, the presence of water and possible diffusion limitations on current density-potential curves and Faradaic efficiencies. A reaction-diffusion model was used that takes into account the effect of electrochemical potential on the stability of intermediates and associated activation barriers in proton-coupled electron transfer steps as well as diffusion of protons and CO2 from the bulk electrolyte to the electrode surface. The basic model can well reproduce hydrogen evolution including the effect of proton diffusion limitations and a shift of proton reduction (low potential) to water reduction (high potential). Considering CO2 electro-reduction, the stepped Cu(211) surface is more active than the Cu(111) terrace towards HCOO(H), CO and CH4. The presence of a catalytic H2O molecule increases the overall rate and selectivity to products (CO and CH4) derived from dissociated CO2. A catalytic H2O molecule facilitates the difficult electrochemical CO2 activation step to COOH and suppresses the competing activation step towards HCOO, which mainly yields HCOO(H). In general, the current densities increase at higher negative potential and the products follow the sequence CO2 → CO → CH4. That is to say, CO2 is converted to CO via COOH dissociation, followed by CO hydrogenation. Trendwise, the simulated product distribution follows the potential-dependent distribution observed in experiment. The low selectivity to CH3OH can be understood from the fast electrochemical steps that lead to CHx-OH dissociation. At high overpotentials the hydrogenation step from CO2 to COOH controls both activity and selectivity towards CH4. At high potential CO2 reduction becomes increasingly diffusion-limited, thus limiting the selectivity of CO2 reduction vs. hydrogen evolution. This aspect supports the need for better design of mass transfer in electrochemical reactors, which operate at high current density.

Plasma Electrolytic Oxidation of High-Strength Aluminium Alloys—Substrate Effect on Wear and Corrosion Performance

With the progress in materials science and production technology and the establishment of light-weight design in many fields of the industry, the application of light metals no longer requires only mechanical strength, but also a significant protection of the material against wear and corrosion. Hard and wear-resistant oxide coatings on aluminium are produced by plasma electrolytic oxidation (PEO). During PEO, a conversion of the aluminium substrate to a ceramic oxide takes place. While the role of strength-giving alloying elements like Cu, Mg/Si, Zn, and Zn/Cu on the PEO process has selectively been subject of investigation in the past, the significance of the alloy composition for the service properties of the coatings is still unknown. Therefore, the performance of PEO coatings produced on the widely used commercial high-strength alloys AlCu4Mg1 (EN AW-2024), AlMgSi1 (EN AW-6082), and AlZn5.5MgCu (EN AW-7075) is examined with regard to their behaviour in the rubber-wheel test according to ASTM G65 and the current density-potential behaviour of the substrates with undamaged and worn coatings in dilute NaCl solution. To give a reference to the unalloyed material the testings were carried out also on Al 99.5 (EN AW-1050) which was treated in an adjusted PEO process. Although differences in the conversion of intermetallic phases during PEO and the phase composition of the coatings on the various substrates are determined, the service properties are hardly depending on the alloying elements of the investigated aluminium materials. The wear rates in the rubber-wheel test are low for all the alloyed samples. The current density-potential curves show a decrease of the corrosion current density by approximately one order of magnitude compared to the bare substrate. Eventually, previous wear of the coatings does not deteriorate the corrosion behaviour. PEO layers on technically pure aluminum can resist the testing regimes if they are prepared in an electrolyte with an elevated silicate content and without additional hydroxide ions, during a longer process time.

Differentiated interactions in phosphate solutions: Comparing Ag(111) and Ag(100) surfaces

The electrochemical behavior of phosphate species on Ag(111) and Ag(100) single crystal surfaces was studied by experimental techniques and theoretical calculations. Characteristic cathodic/anodic potential peaks (Vp) appear in the current density-potential curves (j–V) for H2PO4−, H3PO4, and in the case of PO43− for concentrations lower than 0.1M, where the interaction is stronger for the Ag(100) electrode. This demonstrate that the adsorption is sensitive to the surface structure. The adsorption energy (Eads) of the different species on both surfaces was studied by means of DFT-vdW calculations. All phosphate species have tri-dentate binding. The |Eads| increased for the H3PO4; H2PO4−; HPO42− and PO43− sequence, and the tetrahedral structures are compressed. Although the same trend was observed on both crystalline surfaces, the films have the symmetry of the substrate, C3v and C4v. The influence of hydroxide co-adsorption was studied for different [HPO42−]/[PO43−] ratios in solution. The strength of adsorption obtained from experimental and theoretical calculations show an excellent qualitative correlation.

Influence of Obtaining Method of Nb2O5 Particles Used in Dye Sensitized Solar Cells Consisting of TiO2/ Nb2O5

The niobium pentoxide (Nb 2 O 5 ) is a semiconductor capable of prevent the efficiency loss by recombination in dye sensitized solar cells (DSSC) given the high energy gap. The aim of this study is to investigate the performance of DSSC containing Nb 2 O 5 obtained by Pechini method and hydrothermal synthesis, mixed with TiO 2 nanoparticles. The characterization techniques used were X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering (DSL) and potentiodynamic polarization under power light incidence of 100 mWcm -2 . XRD confirmed obtaining orthorhombic structure niobium pentoxide tested for both methodologies, the SEM showed the best distribution of the oxide obtained by hydrothermal synthesis efficiency was calculated from the current density-potential curves (j-v) confirming the higher efficiency for this sample, about 20% higher. DOI: 10.5935/1984-6835.20160064

Nanostructured Silicon Photocathodes for Solar Water Splitting Patterned by the Self-Assembly of Lamellar Block Copolymers.

We studied a type of nanostructured silicon photocathode for solar water splitting, where one-dimensionally periodic lamellar nanopatterns derived from the self-assembly of symmetric poly(styrene-block-methyl methacrylate) block copolymers were incorporated on the surface of single-crystalline silicon in configurations with and without a buried metallurgical junction. The resulting nanostructured silicon photocathodes with the characteristic lamellar morphology provided suppressed front-surface reflection and increased surface area, which collectively contributed to the enhanced photocatalytic performance in the hydrogen evolution reaction. The augmented light absorption in the nanostructured silicon directly translated to the increase of the saturation current density, while the onset potential decreased with the etching depth because of the increased levels of surface recombination. The pp(+)-silicon photocathodes, compared to the n(+)pp(+)-silicon with a buried solid-state junction, exhibited a more pronounced shift of the current density-potential curves upon the introduction of the nanostructured surface owing to the corresponding increase in the liquid/silicon junction area. Systematic studies on the morphology, optical properties, and photoelectrochemical characteristics of nanostructured silicon photocathodes, in conjunction with optical modeling based on the finite-difference time-domain method, provide quantitative description and optimal design rules of lamellar-patterned silicon photocathodes for solar water splitting.

Thickness determination of electrochemical titanium oxide (Ti/TiO2) formed in HClO4 solutions

Anodic Titanium oxide films were potentiodinamically grown on Ti foil and glass/Ti in 0.010 M HClO4 at 50mVs−1. The current density-potential curves (j−E) showed that the oxide grows according to the physical model for high-field conduction. However, for final potential (Ef) higher than 1.5V vs. Ag/AgCl (sat. KCl) the oxygen evolution reaction becomes more significant, and the formation of bubbles prevented or made more difficult the application of in situ techniques for the simultaneous study of the thickness and optical properties of the anodic layer. We developed a method based on electron probe microanalysis (EPMA) to calculate oxide thickness using ex situ ellipsometry as a reference technique. The normalized intensity of the O Kα peaks was measured for anodic oxides corresponding to Ef values from spontaneous oxide up to 50V, where a linear relationship was observed for a narrower range of final potentials. This behaviour was studied with Monte Carlo simulations. After calibration with ellipsometric results, to take into account sample damage during the electron irradiation, EPMA was applied as a method for thickness determination at Ef ≥ 1.0V. Once the method was established, ex situ thickness determinations became independent of the preparation method of the oxide layer, which represents a comparative advantage against ex situ ellipsometry.

Electrochemical electrolyte spreading studies of the protective properties of ultra-thin films on zinc galvanized steel

Reactive electrolyte spreading along the surfaces of different conversion films on zinc galvanized steel in humid air was monitored visually and with a height-regulated scanning Kelvin Probe. Electrochemical impedance spectroscopy and current density-potential curves revealed that decelerated spreading kinetics are connected with increasing pore resistances of the pre-treatment layers and decreasing oxygen reduction current densities in the electron transfer controlled potential region. After a few days the progress ranking of electrolyte spreading along uncoated conversion films reflected the progress tendencies of cathodic delamination observed on epoxy coated conversion layers after long-time exposure to the same corrosive environment. Such correlation was not discovered for pre-treatment films that do not provide relevant electrochemical barrier properties. The results suggest that oxygen reduction driven electrolyte wetting is an option for accelerated performance testing of anticorrosive ultra-thin films on metal substrates that can be subject to cathodic delamination.

Methanol oxidation on aluminium-copper-silicon alloys coated with polyprrole

Methanol oxidation on the aluminum-copper-silicon alloys which are coated with polyprrole were investigated in 1 N H2SO4 by using electrochemical method. For this purpose, first the current densitypotential curve of alloys were obtained in 1 N H2SO4 + x M pyrrole solutions, determined passive zones are coated with polyprrole alloys in H2SO4 solutions. Then the current-potential curves were obtained in 1 N H2SO4 + x M methanol with aluminum alloys and these are expected at +1.5 V against to the standard calomel electrode (SCE) at the different times in 1 N H2SO4 + 10−3 M pyrrole that were obtained with different scan rates. The extreme methanol oxidation was seen on the E110 and E140 alloys which are coated with polyprrole. Embedded pH electrode solutions which were coated with polypyrrole in 1 N H2SO4 and 1 N H2SO4 + 0.5 M methanol solutions were measured after 30 minutes at +2.1 V.

Current oscillations during the anodic dissolution of copper in trifluoroacetic acid

A phenomenon of current oscillators was characterized crosswise active–passive potential region during the electrodissolution of copper electrode in trifluoroacetic acid (TFA). The current density-potential curves show two transition points. A potential region of current oscillations was found as a part of limiting current region. The Cu|TFA electrochemical oscillator was found to displaying rich dynamical response on varying the temperature and the applied potential. The Cu|TFA system display current oscillation behaviour from the mono-periodic to the mixed-mode (relaxation type). Changes of the electrode surface structure and morphology were investigated by X-ray diffraction spectroscopy, atomic forced microscopy and optical microscopy.

Effect of Substrate on Electroless Co-Base Deposited Films

The deposition behavior and structural and magnetic properties of electroless Co-B and Co-Fe-B deposits, as well as the amorphous ribbon substrates, were investigated. These Co-based alloy deposits exhibited characteristic polycrystalline structures and surface morphology and magnetic properties that were dependent on the type of amorphous substrates. The catalytic activity sequence of the amorphous ribbon electrodes for anodic oxidation of DMAB was estimated from the current density-potential curve in the anodic partial electrolytic bath that did not contain the metal ions. Both the deposition rate and potential in the initial region were obtained in order of the catalytic activity, depending on the alloy compositions of the substrates. The deposition rate linearly varied against the deposition time. The initial deposition potential may have also determined the structural and magnetic properties of the deposit based on the thickness of <TEX>${\mu}m$</TEX> order. Furthermore, a basic study of the electroless deposition processes on an amorphous ribbon substrate has been carried out in connection with the structural and magnetic properties of the deposits.

Electrochemical studies of the inhibition of the cathodic delamination of organically coated galvanised steel by thin conversion films

Scanning Kelvin Probe (SKP) measurements of thin amorphous conversion film coated galvanised steel in combination with current density–potential curves and electrochemical impedance spectroscopy (EIS) were performed with the aim to improve the understanding of electrode potentials at the coating/metal interface and their influence on corrosive de-adhesion. The thin hybrid conversion films contained Zn-phosphates, titanates and also complexing organic compounds and led to an inhibition of the cathodic oxygen reduction and anodic zinc dissolution. In the polymer coated area the conversion film leads to a cathodic shift of the potential as measured by means of the SKP. This cathodic potential shift is explained by the substitution of the n-semiconducting Zn-oxide with an insulating inorganic layer. When the SKP detects the potential of freely corroding iron at a defect, where no protective coating layer is, the interfacial potential for the conversion film coated zinc layer is more negative than the defect potential. This leads to a diminished driving force for an oxygen reduction induced delamination process which is of relevance for the understanding of cut-edge corrosion.

Oscillatory Phenomena during Anodic Copper Electrodissolution in Trifluoroacetic Acid Solution

This work presents the current oscillation phenomena observed in an electrochemical Cu/0.5 M CF3COOH system. The dynamical response of this new oscillator was followed by both current density-potential (j-E) and current density-time (j-t) curves. The current oscillation phenomena of the investigated system were monitored over various potential scan rates and constant applied potentials as control parameters. The increase of potential scan rate significantly decreases both the potential range of current oscillations and the frequency of oscillations. At the j-t curves both the simple and the complex (period adding) oscillations were found. Moreover, with the increase of applied potential, the increase of period of oscillations and current oscillation amplitudes were observed. It appears that the period of current oscillations exponentially grows with applied potential.

Investigation of the macroscopic and microscopic electrochemical corrosion behaviour of PVD-coated magnesium die cast alloy AZ91

The PVD plasma anodisation method developed by the authors allows the anodisation and subsequent PVD deposition of magnesium alloys in a process step using a conventional PVD sputtering unit. In the standard salt spray test, these surfaces show corrosion behaviour superior to conventional hard coatings, and they also show good wear characteristics [H. Hoche, H. Scheerer, E. Broszeit, C. Berger, Mater. Wiss. Werkst. Tech. 30 (2002) 395 [1]; H. Hoche, H. Scheerer, D. Probst, E. Broszeit, C. Berger, Surf. Coat. Technol. 173 (2003) 1018 [2]]. To determine the corrosion behaviour, different test methods were applied to plasma-anodised and Al 2O 3-coated specimens of the magnesium die cast alloy AZ91D and CrN hard coatings with optimised deposition parameters for magnesium alloys. The investigation of the macroscopic electrochemical corrosion behaviour with current density–potential curves (10 mm testing diameters) does not allow any satisfactory description of the quality of the different surface treatments. Measurements with a microprobe (0.1 mm testing diameter) supply a suitable description of the electrochemical corrosion behaviour of PVD-coated magnesium alloys by comparing intact coating areas with specific coating defects produced by Vickers indentations. The results of the three testing methods are compared and brought into agreement with each other. It is shown that conventional macroscopic current density–potential measurements are not suitable to describe the corrosion behaviour of PVD-coated magnesium alloys.

Characterization of thermal and anodic oxide layers on β- and on near-β-titanium alloys for biomedical application

β- and near-β-Ti alloys for biomedical applications show a favourable mix of mechanical, biological and biocompatible properties. In this study, oxide layers on Ti13Nb13Zr, Ti15Mo5Zr3Al, Ti30Nb and Ti30Ta were prepared by thermal and anodic oxidation, in order to adjust constant, reproducible and well-defined surface properties. The thickness, the phase composition and the element composition of the oxide layers were determined. The corrosion properties were investigated by current density-potential curves under physiological conditions. Depending on the oxidation parameters, film thicknesses in the range 10-250 nm can be prepared. The thermal oxide layers consist predominantly of TiO 2 in rutile structure while the anodized samples show a mixture of anatase and amorphous TiO 2 . In addition, certain amounts of mixed oxides of titanium and alloying elements such as TiZrO 4 or TiNb 2 O 7 are found in the oxide films. The corrosion resistance of the oxidized samples is increased as compared with the polished samples whose current densities in the range of passivity are comparable to that of Ti6A14V.

Electrolysis of supercritical aqueous solutions at temperatures up to 800 K and pressures up to 400 MPa

A study on the electrolysis of sub- and supercritical aqueous solutions of sodium hydroxide is presented here. Current density–potential curves are recorded at temperatures up to about 800 K and pressures up to 400 MPa. The molar concentration of the solutions, as referred to T=298 K, is varied from c=(0.01 to 1 ) mol· dm −3 . The autoclave is described in detail. Several electrode materials are examined. The highest reproducibility is obtained with gold electrodes. Some results are also given for platinum, silver and nickel electrodes. Below T=473 K the current–potential curves show the familiar transition from a range of very low currents to an ohmic behaviour with steeply increasing currents above the decomposition potential. The decomposition potential decreases with increasing temperature. Above T=473 K the current–potential curves no longer reflect distinct transitions from low-current to high-current behaviour, and at T=773 K, almost linear current–potential curves are observed over the entire voltage range. Up to current densities of 50 mA· cm −2 , the pressure dependence of the current density at a given potential is marginal. At higher current densities, up to 35 A· cm −2 , a substantial pressure effect is observed.

Preparation of TiO(2) layers on cp-Ti and Ti6Al4V by thermal and anodic oxidation and by sol-gel coating techniques and their characterization.

The excellent biocompatibility of titanium and its alloys used, for example, for medical devices, is associated with the properties of their surface oxide. For a better understanding of the tissue reaction in contact with the oxide layer, knowledge of the chemical and physical properties of this layer is of increasing interest. In this study, titania films were produced on cp-Ti and Ti6Al4V substrates by thermal oxidation, anodic oxidation, and by the sol-gel process. The thickness and structure of the films produced under different conditions were determined by ellipsometry, infrared spectroscopy, and X-ray diffraction measurements. The corrosion properties of these layers were investigated by current density-potential curves under physiological conditions. The oxide layers produced on cp-Ti and Ti6Al4V by thermal oxidation consist of TiO(2) in the rutile structure. For the anodized samples the structure of TiO(2) is a mixture of amorphous phase and anatase. The structure of the coatings produced by the sol-gel process for a constant annealing time depends on the annealing temperature, and with increasing temperature successively amorphous, anatase, and rutile structure is observed. Compared to the uncoated, polished substrate with a natural oxide layer, the corrosion resistance of cp-Ti and Ti6Al4V is increased for the samples with an oxide layer thickness of about 100 nm, independent of the oxidation procedure.