Semiconductor electrochemistry approach to passivity and passivity breakdown of metals and metallic alloys

A critical appraisal of the use of the theory of semiconductors in characterising passive films on metals and alloys is provided, with special emphasis on the use of Mott – Schottky theory for the location of characteristic energy levels of the passive film – electrolyte junction. Some inconsistencies between theory and experimental results in the case of thin passive films are discussed together with possible alternative ways for overcoming such problems. The role of semiconducting properties in determining the pitting behaviour of passive films on W in solutions containing halide is presented and discussed. The validity of a recently proposed correlation between the solid state properties of passive films and the pitting potential is critically reviewed

From ceria nanotubes to nanowires through electrogeneration of base

The preparation of Ce(OH)3/CeO2 nanostructures (NSs) through electrogeneration of base into anodic alumina membranes was studied. The effects of solvent (alcohol and/or water), Ce3? partner anion nature (chloride or nitrate) and concentration, applied potential or current density in driving the morphology toward nanowires (NWs) and/or nanotubes (NTs) was described. The structural analysis performed by X-Ray Diffraction and Raman Spectroscopy allowed to evidence that the presence of Ce(IV) into the nanostructures strongly depends on the oxygen content in the growing environment

Influences of Structure and Composition on the Photoelectrochemical Behaviour of Anodic Films on Zr and Zr-20at.%Ti

photoelectrochemical investigation on anodic films of different thickness grown on sputter-deposited Zr and Zr–20 at.%Ti was carried out. The estimated optical band gap and flat band potential of thick (UF ≥50 V) anodic films were related to their crystalline structure and compared with those obtained for thinner (UF ≤8 V/SCE) anodic oxides having undetermined crystalline structure. The Eg values obtained by photocurrent spectroscopy were also compared with the experimental band gap estimated by other optical ex situ techniques and with the available theoretical estimates of the zirconia electronic structures in an attempt to reconcile the wide range of band gap data reported in the literature. Finally, the optical band gap and flat band potential values obtained for tetragonal Zr0.8Ti0.2O2 mixed oxide were compared with that expected on the basis of a correlation between Eg and the film composition

Overview on performance predictive models – Application to bridge management systems

Bridge management systems (BMSs) have been developed to assist the bridge asset engineers to determine the optimal cost-effective maintenance, rehabilitation, and replacement (MR&R) decisions for bridge networks. The accuracy of these decisions depends significantly on the performance predictive models used to forecast the future condition of infrastructures. The most common performance predictive models used in the BMSs are deterministic and stochastic models. Several limitations in these models have been mentioned by many authors, which leads to a concern about the reliability of these models to effectively define the maintenance strategies. This paper presents an overview of the main performance predictive models that have been applied for infrastructures and recommends the implementation of some of these models in the BMSs.The authors would like to thank ISISE – Institute for Sustainability and Innovation in Structural Engineering (PEst-C/ECI/UI4029/2011 FCOM-01-0124-FEDER-022681) and FCT – Portuguese Scientific Foundation for the research grant PD/BD/128015/2016 under the PhD program “Innovation in Railway System and Technologies- iRail

Recent advances on physico-chemical characterization of passive films by EIS and differential admittance techniques

Thin Nb2O5 anodic films (20 nm thick) grown in phosphoric acid solution have been characterised by EIS and differential admittance study in a large range of potential and frequency. The overall electrical behaviour has been interpreted by means of the theory of amorphous semiconductor Schottky barrier in presence of a non-constant density of states (DOS). A comparison of DOS for films grown in different electrolytes is reported

Effect of Composition on the Photoelectrochemical Behavior of Anodic Oxides on Binary Aluminum Alloys

The photoelectrochemical behavior of anodic films on Al alloys, containing titanium, tantalum, and tungsten (valve metals), has been studied as a function of alloy composition and anodizing conditions. Photocurrent spectroscopy has been used to get information on bandgap and the flatband potential values of different mixed oxides. Both insulator-like and semiconducting behavior has been observed for anodic oxides grown on Al-W and Al-Ti alloys dependent on alloy initial composition. Optical bandgap values, Eg,opt, of different oxides are in accordance with predictions based on the correlation between Eg,opt and the difference of electronegativities of the oxide constituents, indicating potential for tailoring solid state properties of ternary oxides

Methanol and proton transport through chitosan‐phosphotungstic acid membranes for direct methanol fuel cell

Composite chitosan-phosphotungstic acid membranes were synthesized by ionotropic gelation. Their liquid uptake is higher for thin membranes (23 ± 2 μm), while it is lower (~70%) for thicker membranes (50-70 μm). Polarization curves recorded using single module fuel cell at 70°C allowed to estimate a peak power density of 60 mW cm−2 by using 1 M as methanol and low Pt and Pt/Ru loadings (0.5 and 3 mg cm−2) at the cathode and at the anode, respectively. Electrochemical impedance spectroscopy was used to estimate the membrane conductivity and to model the electrochemical behavior of methanol electrooxidation inside the fuel cell revealing a two-step mechanism mainly responsible of overall kinetic losses. Transport of methanol inside the membrane was studied by potentiostatic measurements, allowing to estimate a methanol diffusivity of 3.6 × 10−6 cm2 s−1