Publications

Atmospheric corrosion of iron under a single droplet: A new systematic multi-electrochemical approach

Utilizing a dedicated micro-sized three-electrode cell, this study systematically investigates early-stage electrochemical properties and corrosion behavior of pure iron under single droplets. Various volumes and NaCl concentrations were considered during the evaporation-driven shape and concentration evolution of single droplets. The measurements disclosed that reducing the droplet size from 5 µL to 1.5 µL at 0.01 M NaCl concentration, increased noise resistance (Rn) and polarization resistance (Rp) values. However, at 0.1 M and 0.2 M NaCl concentrations, reducing droplet size led to the domination of relatively high chloride ion concentration over oxygen diffusion, resulting in a very low Rn and Rp, and hence enhanced localized corrosion.

An empirically based finite element method approach for modelling the leaching of lithium carbonate from an active primer system

An integrated modeling approach for atmospheric corrosion in presence of a varying electrolyte film

A Dynamic Electrolyte Film Corrosion (DEFC) model is presented that integrates a model for uniform film condensation/evaporation in presence of salts with a simple model of iron corrosion. The focus is on the role of the film thickness. A limited number of measurements confirms that it is unavoidable to consider the hygroscopic effects. The model is used to simulate the role of sample thickness, heat transfer and changing rates of temperature and relative humidity in well defined climate chamber conditions. Obtained film thicknesses and corrosion rates are simulated using identical input data in absence of salt and for two salts (NaCl and a seawater-like mixture of 90%NaCl-10%MgCl2). The large indirect influence of salts on the corrosion is discussed. Also one-week simulations are performed based on recorded and averaged meteorological data. They show that averaged meteorologic data will lead to incorrect results.

Optical spectroscopy applied to the analysis of medieval and post-medieval plain flat glass fragments excavated in Belgium

Window glass fragments from four Belgian sites were studied and for a set of eighty-five samples the UV-VIS-NIR transmission spectra were analyzed. This collection contains historical and archaeological finds originating from religious buildings namely the Basilica of Our Lady of Hanswijk in Mechelen (17th-20thc) and the Church of Our Lady in Bruges (16th-20thc) as well as from secular buildings as a private house/Antwerp (18th-1948) and the castle of Middelburg-in-Flanders (1448-17thc). All sites contain material on the hinge point between the medieval and the industrial tradition. The variation in composition of the analyzed samples can be explained by the use of different glassmaking recipes, more specifically the use of different raw materials. The composition of window glass differs essentially in the type of flux, using a potash rich fluxing agent until the post-medieval times and industrial soda from the 19th century onwards. A second difference concerns the iron impurities in the glass. For all fragments a clear compositional classification could be made based on the iron concentration. These conclusions were based on archaeological research and drawn after submitting samples to expensive, complex, time-consuming and destructive chemical analyzing methods. Our study indicates that similar conclusions could be made applying the proposed optical based methodology for plain window glass. As a whole, the obtained results make it possible to cluster the fragments for a particular site based on three different sensing parameters: the UV absorption edge, the color and the presence of characteristic absorption bands. This information helps in identifying trends to date window glass collections and indicating the use of different raw materials, production technologies and/or provenance.

<i>In situ</i> ellipsometric and electrochemical characterisation of oxide formed on aluminium in acetate buffer

The paper presents methodology for characterisation of oxide properties on pure aluminium in aqueous solution by use of visual light ellipsometry (VISSE) and electrochemical impedance spectroscopy (EIS) under controlled environmental conditions. Control of the electrode potential and solution pH, chemistry and temperature gives well-defined and reproducible oxide properties. Monitoring the current density during transition between different applied potentials gives direct information about Faradaic changes in the oxide properties, while the ellipsometer monitors the changes in the actual thickness and refractive index of the film. EIS reveals in turn information about the charge transfer processes and adsorption at steady-state conditions. Physical significance of the parameters calculated from the experimental data depends on the accuracy of the mathematical models used. Preliminary results are presented for acetate adsorption and oxide film growth and dissolution kinetics in an aqueous environment. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Intergranular corrosion of AA2024-T3 : initiation and propagation

Influence of microstructure on the corrosion performance of dual phase steels

No abstract is provided for this article.

Unraveling the mechanism of the conversion treatment on Advanced High Strength Stainless Steels (AHSSS)

In this research, a novel governing mechanism has been proposed for the formation of conversion coating on the thermal oxide film of Advanced High Strength Stainless Steels (AHSSS). These new lightweight and engineered materials are being designed to impart emission reduction and solid performance. This coating has been characterized using advanced surface analysis such as HAADF-STEM, GDOES, and ToF-SIMS. The results showed that the conversion components can be found not only on the surface but also at the oxide/metal interface. This deposition in the depth happens preferentially in the Si-poor regions and with the penetration of the conversion components into depth. It was indicated that fluoride ions play an important role to facilitate this penetration by dissolving the less stable components in the oxide film. Dissolution of the Fe in the Fe-Cr solid solution structure results in the formation of a mixed chemical structure containing Cr and P. This novel mechanism brings a new insight into the field of conversion coating when a thick oxide film is present on the top surface.

Development of grained surfaces during EC graining in hydrochloric and nitric acid

No abstract is provided for this article.

Nanoscopic and in-situ cross-sectional observations of Li-based conversion coating formation using liquid-phase TEM

Lithium salts have been proposed as promising environmentally friendly alternatives to carcinogenic hexavalent chromium-based inhibitors for the corrosion protection of aerospace aluminium alloys (AAs). Incorporated into organic coatings, lithium salts are released at damaged locations to establish a conversion layer in which distinct sublayers have different barrier characteristics. Thus, detailed knowledge on the sequence of formation events from the early stages of nucleation towards the final multi-layered arrangement is essential for developing and optimising lithium-leaching technology for protective coatings. Here, liquid-phase-transmission electron microscopy (LP-TEM) is employed to observe nanoscopic morphological evolutions in situ during the lithium-based conversion process of AA2024-T3. Thanks to dedicated preparation of delicate sandwiched TEM specimens allowing us to explore the events cross-sectionally, we provide real-time direct mechanistic information on the conversion process from the initiation to an advanced growth stage. In parallel, we perform supplementary ex situ SEM and TEM investigations to support and validate the LP-TEM findings. The unprecedented experimental approach developed and executed in this study provides an inspiring base for studying also other complicated surface conversion processes in situ and at the nanoscopic scale.

Development of novel surface treatments for corrosion protection of aluminum: self-repairing coatings

Two types of self-repairing coatings for the protection of Al and its alloys are reviewed: (1) organic coatings with capsules containing repairing agent and (2) porous anodic oxide films with inhibitor solution stored in the pores of the oxide film. First, polyurethane microcapsules containing liquid surface-repairing agents were synthesized and polyurethane coating with the capsules was painted on Al alloy specimens. After mechanical damage to the coating, self-repairing occurred by the reaction of water vapor in the air with the repairing agents released from the capsules. Second, porous-type anodic oxide films were formed on Al alloys, and the pores of the anodic oxide films were filled with inhibitor solutions, followed by application of a covering polyurethane layer. Inhibitors released from the pores efficiently protected the Al alloy substrate from corrosion arising from induced mechanical damage.

Monitoring initial contact of UV-cured organic coatings with aqueous solutions using odd random phase multisine electrochemical impedance spectroscopy

In this work, a new methodology is developed to study the initial behaviour of model organic coatings shortly after coming into contact with an aqueous solution, using odd random phase electrochemical impedance spectroscopy (ORP-EIS). The impedance results are resolved over time via the calculation of the instantaneous impedance and fitted with a physically meaningful equivalent circuit. Many physical parameters could be obtained, such as the rapid water uptake, the resistivity of the coatings and the penetration depth of ions in the coatings. The fitting results were verified using differential scanning calorimetry (DSC) and gravimetry.

Triple-Action Self-Healing Protective Coatings Based on Shape Memory Polymers Containing Dual-Function Microspheres

In this study, a new self-healing shape memory polymer (SMP) coating was prepared to protect the aluminum alloy 2024-T3 from corrosion by the incorporation of dual-function microspheres containing polycaprolactone and the corrosion inhibitor 8-hydroxyquinoline (8HQ). The self-healing properties of the coatings were investigated via scanning electron microscopy, electrochemical impedance spectroscopy, and scanning electrochemical microscopy following the application of different healing conditions. The results demonstrated that the coating possessed a triple-action self-healing ability enabled by the cooperation of the 8HQ inhibitor, the SMP coating matrix, and the melted microspheres. The coating released 8HQ in a pH-dependent fashion and immediately suppressed corrosion within the coating scratch. After heat treatment, the scratched coating exhibited excellent recovery of its anticorrosion performance, which was attributed to the simultaneous initiation of scratch closure by the shape memory effect of the coating matrix, sealing of the scratch by the melted microspheres, and the synergistic effect of corrosion inhibition by 8HQ.

Assessment of Carbon-Titanium Multilayer Coatings on Aluminum as Bipolar Plates in PEM Fuel Cells

Aluminum is an appropriate candidate for bipolar plates in proton exchange membrane (PEM) fuel cells because it reduces the final cost and weight of the fuel cell stack in comparison to stainless steel, titanium and graphite. However, a conductive coating layer is essential to protect it against corrosion. In this study, the electrochemical behavior of aluminum coated with titanium and amorphous carbon layers by physical vapor deposition is evaluated. The main goal is to investigate the corrosion protection performance and the possible failure reasons of the coating in sulfuric acid solutions (with different pH values) in the presence of 3 ppm sodium fluoride and elevated temperature (80 °C) to mimic the working conditions of PEM fuel cells. To reach our aim, electrochemical tests are combined with surface analysis techniques. It is revealed that at low pH values (pH = 2 and 3), the coating fails due to the acidity of the electrolyte solutions. However, in the electrolyte with pH = 4, present fluoride ions interfere and consequently lead to localized failures. It is noticed that the presence of defects in the coating is a key parameter in the application of coated aluminum as bipolar plates in PEM fuel cells.

A transmission electron microscopy study of hard anodic oxide layers on AlSi(Cu) alloys

Transmission electron microscopy (TEM) has been employed to examine anodic oxide film formation on 99.8wt.% aluminium, Al–10wt.%Si and Al–10wt.%Si–3wt.%Cu alloys under conditions relevant to hard anodizing. In particular, anodic oxidation of silicon particles proceeded at a significantly reduced rate compared with that of the adjacent aluminium matrix. This gave rise to alumina film encroachment beneath the particles with development of tortuous porosity and, eventually, occlusion of partially anodized particle in the anodic film. Additional effects included the presence of gas-filled cavities above the silicon particles, associated with oxygen generation above the anodizing particle. The presence of such particles and the corresponding gas-filled voids across the anodic film thickness and at the alloy/film interface is considered responsible for the continuous voltage rise during anodizing of the Al–10wt.%Si alloy, effectively blocking electrolyte access to the pore base and providing local region of high resistance at the alloy/film interface. A direct consequence of the voltage rise was a thickening of the barrier layer at the base of the porous anodic film. For the ternary alloy, with the additional presence of copper and the CuAl2 particles, the latter appear to have undergone complete oxidation, with copper detected in local film regions.

An investigation of the corrosion inhibitive layers generated from lithium oxalate‐containing organic coating on AA2024‐T3 aluminium alloy

The protective film formed in a defect by leaching of lithium oxalate from model organic coatings during neutral salt spray exposure has been investigated. A scribed area of about 1 mm width was introduced on the coated AA2024‐T3 aluminium alloy. The scribed area was examined before and after exposure in neutral salt spray environment for 4, 8, 24 and 168 h by scanning and transmission electron microscopies. It was found that the lithium oxalate was able to leach from the organic coating during neutral salt spray exposure and it promoted the formation of a film that provided effective corrosion protection to the alloy. The typical film morphology consists of three different layers, including a relatively compact layer near the alloy substrate, a porous middle layer and a columnar outer layer. Variation of the film morphology was also observed at different locations of the scribed alloy surface, which may be related to the difference of local concentration of lithium species. Electron energy loss spectroscopy detected lithium, aluminium and oxygen in the film. Although the film showed the varied morphologies in different regions of the scribed area, the alloy substrate was protected from corrosion when the film was formed. Copyright © 2016 John Wiley &amp; Sons, Ltd.

New Insights in Nanoelectrodeposition: An Electrochemical Aggregative Growth Mechanism

Supported nanostructures represent the cornerstone for numerous applications in different fields such as electrocatalysis (fuel cells) or electroanalysis (sensors). In contrast to other methods, electrochemical deposition allows the growth of the nanostructures...

Controlling the roughness of aluminium substrates by electrochemical processing

Electrochemical processesing can be used to obtain aluminium surfaces with a well defined roughness. This is based on the use of DC or AC of polarisation of aluminium in an acid eletrolyte containing either chloride or nitrate anions. The roughness is obtained by a controlled pitting process. This DC or AC electrograining process is used for the preparation of aluminium litho material or for the production of Al capacitor foil. In the case of aluminium litho the water retentive properties and the adhesion of the polymer film are important. In the case of capacitor foil it is important to create a very high specific surface area. In the paper the electrochemical process is introduced and the link between the basic electrochemical parameters, such as aluminium alloy composition, current density, electrolyte composition, type of the anion in relation to the obtained morphology is discussed.