Multifunctional epoxy coatings combining a mixture of traps and inhibitor loaded nanocontainers for corrosion protection of AA2024-T3

This work aims at investigating the corrosion protection effectiveness of multifunctional epoxy coatings modified with pigments such as ceramic nanocontainers loaded with corrosion inhibitor, chloride and water traps, applied on AA2024-T3. Characterizations on the morphology, composition and structure of the coatings were conducted. The corrosion resistance was studied by electrochemical impedance spectroscopy, localized electrochemical impedance spectroscopy and scanning vibrating electrode technique. The mechanical behaviour of the coatings was examined through nanoindentation and nanoscratching tests. Electrochemical and nanomechanical testing results, evidenced the improvement of the corrosion protective properties and mechanical behaviour of the coatings in the presence of the various pigments.     

Corrosion behaviour of Al/Al3Ti and Al/Al3Zr functionally graded materials produced by centrifugal solid-particle method: Influence of the intermetallics volume fraction

Intermetallic particles, Al₃Ti and Al₃Zr were formed in Al–5mass%Ti and Al–5mass%Zr alloys, respectively, by centrifugal casting, in order to create functionally graded materials (FGMs). At present, no information is available on the influence of the amount of intermetallics on the electrochemical properties of these alloys.In this paper, the corrosion resistance of Al/Al₃Ti and Al/Al₃Zr FGMs was investigated by open-circuit measurements, potentiodynamic polarization and electrochemical impedance spectroscopy. Results suggests that the corrosion resistance of the FGMs is affected by galvanic effects between the intermetallic particles and the metallic matrix. Lower centrifugal forces resulted in an improvement of the electrochemical properties.     

Influence of the surface activation and local pitting susceptibility on the AC-electrograining of aluminium alloys

AC electrograining of aluminium is strongly influenced by the surface microstructure. The mechanical and electrochemical properties of the sub-surface present in aluminium alloys affect the electrochemical reactions that prevail during electrograining. Etching pre-treatment of aluminium removes intermetallics and rolled-in oxides; as a result, the attack on the aluminium substrate starts with the initial cycles of the electrograining process. Local electrochemical investigations show differences in corrosion and passivation properties between rolled-in oxides and clean surfaces. The interface between rolled oxides and aluminium matrix acts as a weak point for pit initiation.     

Corrosion of metals in wood: Comparing the results of a rapid test method with long-term exposure tests across six wood treatments

This paper compares two methods of measuring the corrosion of steel and galvanized steel in wood: a long-term exposure test in solid wood and a rapid test method where fasteners are electrochemically polarized in extracts of wood treated with six different treatments. For traditional wood preservatives, the electrochemical extract method correlates with solid wood exposure which suggests that the reduction of cupric ions is the cathodic reaction in both the solid wood and the extract. For treatments without copper, the extract method predicted a higher corrosion rate than the solid wood exposure. For these treatments, the cathodic reaction appears to be the reduction of acid and dissolved oxygen. The practical implication of this work is that in some cases, the rapid test method could be used to screen new fasteners and wood preservatives. Scientifically, this work increases the understanding of the mechanism of corrosion of fasteners in treated and untreated wood.     

Improving the corrosion behaviour of powder metallurgical 316L alloy by prepassivation in 20% nitric acid

The electrochemical improvement of PM 316L stainless steels by pre-alloyed powder prepassivation in 20% nitric acid in comparison with as-received specimens has been studied in this work. For comparison purposes a simultaneous study was carried out on similar composition wrought AISI 316L steels. Corrosion resistance was studied using evolution of the corrosion potential vs. time, anodic polarisations curves and Zero Resistance Ammeter technique. Reductions of the corrosion rate (i_corr) were observed in prepassivated specimens in neutral chloride media. Crevice resistance was higher for prepassivated specimens and for higher densities and annealing as post-heat treatments.     

Effect of silica nano-particles on the performance of manganese-based conversion treatments

Permanganate-based conversion treatments incorporating silica nano-particles + nitrate ions or other inhibitive additives have been examined by corrosion and adhesion tests on samples coated with paint and by polarisation measurements on treated, but uncoated AA 3003 panels. Although electrochemical behaviour is not improved by addition of the silica nano-particles, in many cases they substantially improve the performance of PVDF-coated samples in adhesion and accelerated corrosion tests.     

Effect of rapid solidification on the microstructure and corrosion behaviour of Al-Zn-Mg based material

The corrosion behaviour of Al-5Zn-3Mg-0.6Cu-0.8Zr-0.25Cr-0.15Ni-0.15Ti alloys, produced by traditional and powder technologies, with similar thermo-mechanical treatments, in 3% sodium chloride solution, has been examined by electrochemical methods, scanning electron microscopy, transmission electron microscopy and X-ray microanalysis. The alloys reveal similar precipitation but of different shape, size and distribution; further, both alloys experience localized corrosion. Copper-rich precipitates initiate the dissolution of surrounding particles, enriched in Zn and Mg. As a result, the surface is enriched with other alloying elements after a full polarisation run. Cast material has lower corrosion properties because of the higher heterogeneity of the structure. The structure heterogeneity of the cast material involves a more non-uniform distribution of the precipitates, larger Zn- and Mg-rich particles, and depletion of the matrix and areas around the precipitates by alloying elements compared with the powder material.     

A study of the corrosion behavior of gamma titanium aluminide in 3.5 wt% NaCl solution and seawater

Gamma titanium aluminide (γ-TiAl) was evaluated for corrosion resistance in 3.5% NaCl and seawater using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Polarization plots indicate very low corrosion rates although in both electrolytes the control samples lost passivity at low polarization potentials. Surface modification treatments were employed by oxidizing the samples in air at 500 °C and 800 °C with the purpose of improving corrosion resistance. While the surface treatments rendered γ-TiAl passive in the polarization experiments in both electrolytes, EIS tests showed that the oxide formed at 800 °C was not protective. EEC models are proposed to explain the EIS results for the three surface conditions tested.     

Electrochemical corrosion behavior of a novel antibacterial stainless steel

A novel antibacterial stainless steel (ASS) with martenstic microstructure has been recently developed, by controlled copper ion implantation, as a new functional material having broad-spectrum antibacterial properties. The electrochemical corrosion behavior of the ASS in 0.05 mol/L NaCl was assessed using linear polarization and electrochemical impedance spectroscopy (EIS) and compared with that of a conventional stainless steel (SS) without copper ion implantation. The ASS exhibited higher corrosion susceptibility in the chloride medium; with a more negative (active) corrosion potential, higher anodic current density and lower charge transfer and polarization resistance. This has been attributed to the occurrence of copper-catalyzed interfacial reactions. A functional tool, 3-D presentation of EIS data, has been employed in analyzing the electrochemical corrosion processes as well as probing complex interfacial phenomena.     

Effect of antimony, bismuth and calcium addition on corrosion and electrochemical behaviour of AZ91 magnesium alloy

This study investigated the effect of antimony, bismuth and calcium addition on the corrosion and electrochemical behaviour of AZ91 magnesium alloy in 3.5% NaCl solution. Techniques including constant immersion, electrochemical potentiodynamic polarisation, scanning electron microscopy (SEM), energy dispersed spectroscopy (EDS) and X-ray diffraction (XRD) were used to characterise electrochemical and corrosion properties and surface topography. It was found that corrosion attack occurred preferentially on Mg₃Bi₂ and Mg₃Sb₂ particles while Mg₁₇Al₈Ca_0.5 and Mg₂Ca phases showed no detrimental effect on corrosion. Combined addition of small amounts of bismuth and antimony to the AZ91 alloy resulted in significant increase in corrosion rate.     

On the corrosion of binary magnesium-rare earth alloys

The corrosion properties of high-pressure die cast (HPDC) magnesium-rare earth (RE) based alloys have been studied. Binary additions of La, Ce and Nd to commercially pure Mg were made up to a nominal 6 wt.%. It was found that the intermetallic phases formed in the eutectic were Mg₁₂La, Mg₁₂Ce and Mg₃Nd, respectively. Results indicated that increasing RE alloying additions systematically increased corrosion rates. This was also described in the context of the electrochemical response of Mg-RE intermetallics - which were independently assessed by the electrochemical microcapillary technique.This study is a discrete effort towards revealing the electrochemical effect of carefully controlled binary alloying additions to magnesium in order to elucidate the microstructure-corrosion relationship more generally for HPDC Mg alloys. Such fundamental information is seen to not only be useful in understanding the corrosion of alloys which presently contain RE additions, but may be exploited in the design of magnesium alloys with more predictable corrosion behaviour. There is a special need to understand this relationship - particularly for magnesium that commonly displays poor corrosion resistance.     

Microstructure effects on the electrochemical corrosion properties of Mg – 4.1% Ga – 2.2% Hg alloy as the anode for seawater-activated batteries

Mg–Ga–Hg alloy is a new material with special electrochemical corrosion properties that make it ideal for use in seawater-activated battery anodes. The effects of microstructure and phase transformation on the electrochemical properties of the Mg – 4.1% Ga – 2.2% Hg alloy were studied and compared with Mg–Al system alloys. The results show that the Mg – 4.1% Ga – 2.2% Hg alloy, when used as an anode, has an appropriate corrosion potential in a half-cell test and superior electrochemical properties in a single cell assembled with CuCl. The Mg₃Hg and Mg₂₁Hg₅Ga₃ phases of the alloy influence its corrosion behaviour and provide a steady corrosion potential during the discharge process.     

Electrochemical study of modified cerium-silane bi-layer on Al alloy 2024-T3

In this paper, the performance of bis-1, 2-(triethoxysilyl) ethane (BTSE) as a pre-treatment to protect the AA 2024-T3 against corrosion has been investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves, and the scanning vibrating electrode technique (SVET). The microstructural and morphological characterizations were carried out via scanning electron microscopy and atomic force microscopy and the chemical composition evaluated using contact angle measurements and X-ray photoelectron spectroscopy (XPS). The electrochemical results showed that the additives improved the anticorrosion properties of the coating. The chemical characterization indicated that additives contribute to an increased degree of surface coverage, as well as to a more complete reticulation. The SVET results evidenced the self-healing abilities of Ce ions.     

Use of vapour phase corrosion inhibitors in packages for protecting mild steel against corrosion

Some aspects of the passivation of mild steel in the presence of selected vapour phase corrosion inhibitors (VCIs) were considered. In particular their ability to vapourize was evaluated by sublimation tests and their role in the inhibition mechanism of mild steel was investigated by electrochemical methods such as open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) measurements. In the presence of some carboxylates, amines and azoles alone and as mixtures a protective layer can be formed on mild steel in neutral and alkaline solution. It was shown that the passivation mechanism strongly depends on the pH of the solution. In addition the influence of contaminants from industrial alkaline cleaning baths on the protective properties was analyzed.     

Effect of alternating voltage treatment on the corrosion resistance of pure magnesium

Pure magnesium was treated by alternating voltage (AV) treatment technique. The optimal AV-treatment parameters for greatly improving corrosion resistance were determined by the orthogonal experiments. Polarization curves, electrochemical impedance spectroscopy (EIS), and scanning electrochemical microscopy (SECM) were performed to understand the effect of AV-treatment on the corrosion resistance of pure magnesium. AFM, contact angle measurement and XPS were employed to further investigate the influence of AV-treatment on the properties of the surface film formed on pure magnesium after AV-treatment. The results showed that a uniform and stable film was formed and the corrosion resistance of pure magnesium was greatly improved after AV-treatment. This was caused by the noticeable change of chemical structure and semi conducting properties of surface film after AV-treatment.     

Intergranular corrosion of welded joints of austenitic stainless steels studied by using an electrochemical minicell

An intergranular corrosion study of welded joints of austenitic stainless steels (AISI 304 and 316L) has been addressed. A specific small-scale electrochemical cell (minicell) has been used. Four different weldment zones have been studied. The electrochemical methods applied were the electrochemical potentiokinetic reactivation test and electrochemical potentiokinetic reactivation double loop test. These techniques showed that the HAZ was the most critical zone to intergranular corrosion for both materials. The weld metal was susceptible to interdendritic corrosion and the fusion line showed a mixture of intergranular and interdendritic corrosion. The effect of pre- and post-welding heat treatments for AISI 316L was analyzed. The HAZ was again the most critical zone in every heat treatment condition. The results were correlated to the microstructural features of the materials.     

Using EIS to analyse samples of Al–Mg alloy AA5083 treated by thermal activation in cerium salt baths

This paper describes a study undertaken of the morphological and anticorrosive characteristics of surface layers formed on the Al–Mg alloy AA5083 from solutions of Ce(III), by means of various heat treatments while immersed in baths of cerium salts. SEM/EDS studies have demonstrated the existence of a heterogeneous layer formed by a film of aluminium oxide/hydroxide on the matrix and a series of dispersed islands of cerium deposited on the cathodic intermetallics. With the object of evaluating the degree of protection provided by the layers formed and of characterising the particular contribution of the electrochemical response of the system in NaCl, the results obtained by means of EIS are presented and discussed.     

Influence of pH on the electrochemical behaviour of a duplex stainless steel in highly concentrated LiBr solutions

The objective is to study the influence of pH on the corrosion and passive behaviour of duplex stainless steels (DSS) using potentiodynamic measurements, potentiostatic tests and electrochemical impedance spectroscopy (EIS).DSS are spontaneously passive in heavy brine LiBr solutions. Under potentiostatic conditions at applied anodic potentials within the passive domain an equivalent circuit with two time constants is the most suitable model to describe the corrosion mechanism in the interface electrolyte/passive film/metal. pH modifies the electrochemical properties of the passivity of the alloy in a 992 g/L LiBr solution reducing its resistance with the applied potential.     

In situ monitoring of a Mg-rich primer beneath a topcoat exposed to Prohesion conditions

Mg-rich primers have been proven to be an adequate alternative for chromate-based coatings for the protection of aluminum alloys from corrosion. The performance of a Mg-rich primer on aluminum 2024-T3 under Prohesion® exposure (ASTM G85) has been monitored using an embedded sensor placed at the surface of the primer and below the topcoat.Electrochemical impedance spectroscopy and noise measurements were conducted to monitor the electrochemical properties of the system beneath the topcoat. The data analysis demonstrates that the sensor is able to detect change in the barrier properties of the topcoat in response to the exposure conditions.     

Characterisation of the oxide layer on carbon steel during hot conditioning of primary heat transport systems in heavy-water reactors

The corrosion layer formation on carbon steel during hot conditioning of primary heat transport systems of pressurised heavy-water reactors has been characterised using ex-situ methods (gravimetry, electron microscopy, X-ray diffractometry). In addition, the electric and electrochemical properties of the corrosion layers have been followed in-situ by voltammetry and electrochemical impedance spectroscopy during exposure to simulated hot conditioning water chemistry. The corrosion layer formed has been found to be a bilayer oxide of the inverse spinel type. The impedance data have been quantitatively interpreted using the Mixed-Conduction Model for oxide films allowing for the estimation of certain kinetic parameters at the compact layer/electrolyte interface. The obtained results point out to the fact that the electric and electrochemical properties of the carbon steel are determined by the processes in a thin n-type semiconductor layer and at its interface with the electrolyte.