Table of contents

Hydrogen absorption into steel membrane was studied using an electrochemical hydrogen permeation technique. The investigations were conducted in the H2SO4 + Na2SO4 solutions with the constant ionic strength equal to 1 and pH equal to 1.80 and 1.13. The influence of CNS- anions has been studied. The Iyer, Pickering, Zamanzadeh (IPZ) analysis of the measured steady-state hydrogen permeation rates gives the rate constants of the steps of the HER, hydrogen surface coverage OH, exchange current density, io, and kinetic-diffusion constant. The kinetic parameters of the HER have been estimated at a constant potential and a constant hydrogen overpotential. These data testify about the Volmer rate determining step (rds) in the HER.

The influence of the water concentration (0.15-50 wt.%) and pyridine one (0.5-10 mM) on the hydrogen overvoltage (η) on iron has been studied in the ethylene glycol - water solutions of HCl (0.05-0.99 M). The measurements were conducted in the solutions with the constant ionic strength equal to 1 (LiCl was used) and in the hydrogen atmosphere at the room temperature. The rate-determining step of the HER and η depend on the concentration of water and pyridine in the solutions.

Electrochemical synthesis of pyrrole on mild steel substrate was carried out by potentiodynamic and galvanostatic techniques from neutral aqueous sodium tartrate medium. Homogenous and adherent PPy layer was achieved by galvanostatic technique at current density 5 mA cm-2. Basic physical vapor deposition (PVD) coatings (TiN, CrN and DLC) deposited on mild steel were used for comparison of corrosion properties with PPy film. The main problem of PVD coatings in the corrosive media is their porosity. Electrochemical deposition of PPy was applied as a solution for the porosity. PPy film was successfully deposited on PVD coatings by the galvanostatic technique. The protection against corrosion was studied in 3% NaCl solution by several electrochemical methods - measurement of potentiodynamic polarization curves, Tafel plot analysis and EIS method.

From antiquity bronzes have been widely used to produce sculptures and others objects of art. Bronze artefacts are generally covered with a patina. The patina formed in a long term exposition acquired often a certain protective effect of the substrate metal, but a recent increase of air pollution and/or acid rain damage the bronze exposed in urban environment. A method that reinforces a protective effectiveness of patina becomes therefore necessary. In order to preserve metal works from the aggressive atmosphere, organic inhibitors are often required. The inhibiting effects of two non-toxic organic inhibitors: 1- phenyl-4-methylimidazole and 1-(p-tolyl)-4-methylimidazole on the patina were examined by potentiodynamic methods and electrochemical impedance spectroscopy as well as spectroscopic methods. The morphology and crystallographic structure of artificially obtained patina without and with inhibitor layer were examined with SEM and EDS analyses. The results of these investigations have shown that both studied inhibitors protect patina in aggressive media.

Co-Cr-Mo alloys have been widely used as biomaterials to assist in the repair or replacement of bone tissue in the human body. In this study the influence of alloying elements on the properties of passive films, which are vital to the alloy's biocompatibility, was studied. In-vitro investigations were performed in a physiological Hank's solution with a pH of 6.8. Electrochemical techniques were used to study the oxido-reduction processes, while the structural properties of the electrified interfaces and the solid-state processes and changes inside the oxide films were studied using electrochemical impedance spectroscopy. The film's composition as a function of the applied potential was examined using X-ray photoelectron spectroscopy. A quantitative analysis of the metallic ions produced during a prolonged immersion of the investigated materials in the Hank's solution was carried out by high-resolution inductively coupled plasma mass spectrometry (HR ICP-MS). A good correlation between the results obtained from the different experimental techniques was obtained.

Abstract: High-speed electrogalvazing have attracted increasing interest from the automobile industry and steelmakers because of it's high efficiency and excellent mechanical properties. Flow velocity of electrolyte is closely related to the coating properties especially roughness and texture. Effect of flow velocity of sulfate electrolyte electrogalvazing on morphology, roughness and crystal orientation of zinc deposit, was studied with self-made simulative gravity high-speed plating bath. The results showed that effect of flow velocity on micromorphology of zinc deposit was evident: High velocity got dense and smooth deposit, while slow velocity resulted in rough and convexoconcave one. Foremost in this study, it was found that there was linear decline of deposit roughness with the increase of flow velocity, the formula of this relationship established in this paper was: Ra=a+bv, further study on which confirmed the discipline of effect of deposit thickness and current density on deposit roughness.

Barrier type anodic oxides on aluminum-magnesium (Al-Mg) alloy in nonaqueous electrolyte solution are found to feature some excellent characteristics. Surface micro roughness is found by far less than that grown in aqueous electrolyte solution. Moisture outgassing from the barrier anodic oxides is very much limited. Even at elevated temperature, the barrier anodic oxides develop no heat cracks. They feature outstanding resistance to corrosive process gases. Anodization of Al-Mg alloys in nonaqueous electrolyte solution will be promising surface passivation of the semiconductor vacuum chambers.

Some of the physico-electrochemical properties of passive oxide films that form on reactive metal and alloy surfaces, and which protect the underlying metals from reaction with corrosive environments, are reviewed within the context of the Point Defect Model (PDM). This model yields analytical expressions for the steady state current and film thickness and for the transients in these properties that can be used to predict deterministically the accumulation of general corrosion damage to metal surfaces, provided that the evolutionary path to the future state is continuous and can be specified. The conditions under which passivity may exist are defined in terms of Phase Space Analysis (PSA) of the PDM and it is found that passivity is invariably a meta-stable phenomenon. PSA leads to the development of Kinetic Stability Diagrams (KSDs) as alternatives to the equilibrium thermodynamic Pourbaix diagrams that are now used to describe the conditions under which passivity is observed.

The analysis of the Electrochemical Quartz Crystal Microbalance (EQCM) and Electrochemical Impedance Spectroscopy (EIS) results are consistent with a nickel electrodissolution process limited by the passage of Ni(I) to Ni(II), when chloride ions are present in the acid sulphate medium, or by the passage of Ni(II) to Ni2+ in solution, in absence of chloride. This interpretation allows explaining the potential evolution of Fdm/dQ values in both experimental conditions by assuming the formation of a new phase on the electrode surface with a gel-like structure placed between the metal and the solution. Ni(I) surface concentration is calculated from the instantaneous mass/charge Fdm/dQ values.

Localized corrosion formed on an Al-based metal-matrix composite (MMC) reinforced with 40 wt% Si particles in an air-exposed 0.5 M Na2SO4 solution. Scanning vibrating electrode technique revealed that the net currents over the localized corrosion region were cathodic. Scanning ion-selective electrode technique revealed that the solution near the localized corrosion region was alkalized. Scanning electron microscopy indicated that corrosion initiated around Fe-containing intermetallic particles, which serve as cathodic sites. It is hypothesized that during the processing of the Al/Si MMC, inter-diffusion causes Al atoms to diffuse into Si particles forming a layer of highly p-doped Si at the Al/Si interface. Thus, following the immersion of the MMC into the Na2SO4 solution, at the sites adjacent to the Fe-containing intermetallic particles where the Al matrix dissolved, highly p-doped Si surfaces were exposed to the solution. The highly p-doped surfaces can therefore serve as cathodic sites and exacerbate corrosion.

Discoloration and corrosion of components can lead to a wide variety of problems, ranging from poor cosmetic appearance to complete deterioration. Whether a component undergoes superficial surface discoloration or severe corrosion, a systematic approach is needed in order to properly identify the cause of the problem so that proper corrective measures can be taken. Many different analysis techniques are available for characterizing surface discoloration and corrosion deposits, and the proper use of the appropriate techniques will greatly increase the likelihood of correctly identifying the physical cause of the problem. This article details an effective failure analysis process for evaluating discolored and corroded parts.

The present study explores the formation of corrosion products on the steel surface in reinforced concrete in conditions of corrosion and subsequent transformation of these layers in conditions of cathodic protection (CP). Of particular interest was to investigate if the introduced pulse CP (as cost- effective alternative of CP) will lead to similar (or even better) transformation of the product layers on the steel surface, compared to conventional techniques. Qualification and quantification of the studied layers was performed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray analysis (EDAX), visualization of morphology and products distribution was achieved using environmental SEM (ESEM).

The DC polarization and AC EIS techniques were used to analyze the electrochemical reaction behavior of Alloy AZ91 in H3PO4/KOH buffered K2SO4 solution at pH 7. The corrosion resistance of Alloy AZ91 was directly related with the stability of Al2O3.xH2O rich part of the composite oxide/hydroxide layer on the alloy surface. The mf capacitive loop arose from the relaxation of mass transport in the solid oxide phase. The lf inductive loop had tendency of disappear when the dissolution rate of the alloy decreased as a result of the formation of the protective oxide layer.

Oxide growth and thermal degradation of three ferritic SOFC interconnector alloys have been investigated. The materials included a standard grade (alloy 430) and two alloys (Crofer 22 APU, ZMG 232) specifically designed for interconnector service. All alloys appear to follow parabolic oxidation up to 500 h at 740{degree sign}C in air. During oxidation, a consistent decrease of iron and increase of chromium and manganese were observed in the surface oxide. Some chromium transport was detected on the cathode side surface of the cell after 500 h at 740{degree sign}C. The results emphasise the importance of appropriate coating of the interconnectors, to prevent chromium poisoning on the cathode. A natural coating material would be similar or compatible with the ceramic cathode. Such a coating also has the additional advantage that simpler and cheaper steel grades could be used as the interconnector material.

Corrosion of 70/30 Cu-Ni alloy by marine aerobic bacteria Pseudomonas sp. NCIMB 2021 in an artificial seawater medium was investigated by electrochemical and microscopic methods. Polarization curve measurements demonstrated that the corrosion rate of the alloy increased notably in the presence of the Pseudomonas sp. by the acceleration of both the anodic and cathodic reactions. The impedance spectra and the corresponding equivalent circuits confirmed that the alloy surface in the sterile medium comprised of an outer organic compound conditioning layer and an inner compact and protective oxide film layer; while in the Pseudomonas inoculated medium, a duplex layer of an outer porous, heterogeneous and non-protective biofilm layer and an inner porous oxide film layer was present. Both the charge transfer resistance, Rct, and the resistance of the porous oxide film, Rpo, decreased with exposure time, indicating an acceleration of corrosion due to the marine bacteria. Bacteria attached to the alloy surface formed blotchy biofilms, as observed by fluorescent microscopy. The dynamic development of the biofilm and surface roughness were monitored by atomic force microscopy. Scanning electron microscopy images showed micro- pitting corrosion on the alloy surface after the biofilm remova

It was investigated α-alanine and asparagine acid influence on copper anodic process kinetics in alkaline electrolytes. The experiments were carried out at two systems: I - 0.01 M NaOH +X M α-Ala (X=10-4/10-1 M) and II - 0.01 M NaOH +X M Asp (X=10- 5/10-3 M). It was found out that α-alanine (from СAla= 5*10-3 М to 2*10-2 М) and asparagine acid (from СAsp=1*10-5 to 1*10-3 М) stimulate anodic processes at passive region and cause of metal local activation. However except this general regularity, the individual singularity at both systems were found out: at the I system local activation develops under ЕLA=0.10-0.20 V, at the II system two local activation potentials were identified Е1LA=0,23-0,34 V and Е2LA =0.70-0.85 V, which were divided by repassivation region.