Publications

The most common accelerated corrosion test used for aluminum brazing sheet is the Sea Water Acidified Accelerated Test (SWAAT). However, still some ambiguity exists, indicating that the test suffers from significant scattering of the results. Keeping the climatic parameters constant, this study elucidates how the variations of the test results are material dependent. Applying a new statistical reliability evaluation and interpretation method, it was shown that the SWAAT test is valid for product performance comparison purposes. Comparing the corrosion mechanism and morphology of attack it was proved that the SWAAT performance of the material can be reflected in potentiodynamic responses.

In the present study, the effect of different types of iron oxides, which naturally exist on steel substrate, on the interfacial interaction between an epoxy coating and a carbon steel substrate was studied at the molecular/atomic level by employing molecular dynamics (MD) simulations and quantum mechanics (QM) calculations. Three types of iron oxide, that is, ferrous oxide (FeO), ferric oxide (Fe2O3, hematite), and ferrous ferric oxide (Fe3O4, magnetite), were considered for modeling, and their binding energies were calculated and compared by altering the concentration of hydroxide groups on the surface. To probe the effect of curing agent on interfacial interactions, computations were performed for either uncured or aminoamide-cured epoxy resins. The effect of the acid–base properties of the iron oxide on the molecular bonding was theoretically investigated by imposing diverse iron hydroxide/oxide termination groups. Noticeably, MD and QM calculations confirmed rather well earlier experimental evaluations on iron oxide acid–base properties obtained through X-ray photoelectron spectroscopy measurements in the view of chemisorption of different epoxy compounds. However, the interaction behavior of cured epoxy with hydroxylated iron oxide surfaces was quantified mechanistically in the current work from a closer view. For instance, it was found that aminoamide-cured epoxy was adsorbed on all oxide substrates through a mechanism of electrostatic and donor–acceptor interactions, with binding energies of −113.6, −1035.9, and −304.4 kcal/mol respectively assigned to FeO, Fe2O3, and Fe3O4 iron oxides. In the case of a hydroxylated surface, aminoamide-conjugated epoxy adhesive was found in the hydrogen bond interface as well, which was evidence of strengthened binding at a surface populated by hydroxide groups. Moreover, theoretical explorations showed that the type of covalent linkage between the curing molecule and epoxy resin governs the extent of cured epoxy adhesion to the surface of iron oxide.

(Attention for corrosion science, the abstract must not exceed more than 100 words) In this research, first a multi-analytical approach was carried out to propose a mechanistic model for the formation of the thermal oxide film on low Cr stainless steel. It describes the effects of kinetically and thermodynamically driven phenomena on the growth of a Fe-Cr complex oxide film at 950℃. Second, the behavior of the thermal oxide film in the presence of fluoride ions, as a relevant pickling agent in conversion treatment, was investigated. It was shown that fluoride ions enter the oxide film and form a complex with Fe and preferentially dissolve hematite islands through a complexation mechanism.

Type III deep eutectic solvents (DES) have attracted significant interest as both environmentally friendly and functional solvents that are, in some ways, advantageous to traditional aqueous systems. While these solvents continue to produce remarkable thin films and nanoparticle assemblies, their interactions with metallic surfaces are complex and difficult to manipulate. In this study, the near-surface region (2–600 nm) of a carbon surface is investigated immediately following silver nanoparticle nucleation and growth. This is accomplished, in situ, using a novel grazing transmission small-angle X-ray scattering approach with simultaneous voltammetry and electrochemical impedance spectroscopy. With this physical and electrochemical approach, the time evolution of three distinct surface interaction phenomena is observed: aggregation and coalescence of Ag nanoparticles, multilayer perturbations induced by nonaggregated Ag nanoparticles, and a stepwise transport of dissolved Ag species from the carbon surface. The multilayer perturbations contain charge-separated regions of positively charged choline-ethylene and negatively charged Ag and Cl species. Both aggregation-coalescence and the stepwise decrease in Ag precursor near the surface are observed to be very slow (∼2 h) processes, as both ion and particle transport are significantly impeded in a DES as compared to aqueous electrolytes. Altogether, this study shows how the unique chemistry of the DES changes near the surface and in the presence of nanoparticles that adsorb the constituent species.

No abstract is provided for this article.

The atmospheric corrosion of carbon steel was monitored by a Fe/Cu type galvanic corrosion sensor for 34 days. Using a random forest (RF)-based machine learning approach, the impacts of relative humidity, temperature and rainfall were identified to be higher than those of airborne particles, sulfur dioxide, nitrogen dioxide, carbon monoxide and ozone on the initial atmospheric corrosion. The RF model demonstrated higher accuracy than artificial neural network (ANN) and support vector regression (SVR) models in predicting instantaneous atmospheric corrosion. The model accuracy can be further improved after taking into consideration of the significant effect of rust formation on the sensor.

No abstract is provided for this article.

The overall performance of any organic coating system on a metal is largely dependent on the primer coating which has the crucial function to ensure adhesion to the metal substrate. Although performance in terms of adhesion can be empirically measured, the underlying chemical adhesion mechanism is difficult to unravel. A detailed molecular characterization of interfacial chemistry is required for this purpose, but brings up the challenge to reach the buried interface without inducing excessive damage to its molecular structure. In this work, argon gas cluster ions are being applied to sputter through an aminosilane coating on steel, in order to access the steel oxide–silane interface with time-of-flight secondary ion mass spectrometry (ToF-SIMS). In situ atomic force microscopy measurements during the sputter process demonstrate the importance of optimizing the Ar gas cluster ion beam in order to minimize sputter-induced roughness and molecular damage. ToF-SIMS spectra obtained at the buried steel oxide–aminosilane interface accessed by sputtering were compared to spectra from a steel oxide–aminosilane interface that was directly accessible without the need for sputtering. This comparison allowed us to identify contributions from sputter-induced damage in the buried interface spectra. Fragments characteristic for interfacial bonding interactions could be extracted, although there is a significant loss of molecular information because of sputtering. Nevertheless, insights into the role of steel surface hydroxyl groups in the adsorption mechanism of aminosilanes could be obtained through deuteration of the steel substrate.

This work focuses on the effect of surface roughness and surface chemistry on the initial adhesion strength and corrosive de-adhesion properties of adhesive bonds. The adherend used in this study is a S690 low-alloy steel whereas the adhesive is a 2-component epoxy-amine adhesive (Araldite 2015). The steel surface is subjected to different surface pre-treatment methods such as mechanical abrasion, grit blasting, zirconium conversion treatment and silane treatment. The effect of these different pre-treatments on the surface morphology, roughness and chemistry is addressed. Single-lap joint tests were performed at ambient conditions to assess the initial bond strength of the joint. Static wedge tests were performed in saltwater immersions to study the environmental ageing of the adhesive joints. Unloaded delamination of adhesive films from the steel surface was studied by means of scanning Kelvin probe (SKP) at high relative humidity. This unique combination of different techniques allows thorough evaluations of the bond performance under different environmental and loading conditions. Experimental results indicate that surface roughening plays an important role in the initial adhesion in the single-lap joint test but a minor role in the durability of the bonded steel surfaces. The improved initial adhesion is mainly attributed to the increased interfacial bond area at higher surface roughness. The presence of complex texture or morphology shows a more profound effect than the average roughness on both the initial adhesion and the durability of the interfacial adhesion. The results from the static wedge test show the large contribution of mechanical interlocking, caused by texturing of the surface, on the durability of the interfacial adhesion. In the absence of complex texture, surfaces with altered chemistry by zirconium- or silane treatment exhibit a significant increase of the initial bonding strength due to enhanced physicochemical interactions across the interface. Assessment of the interfacial delamination kinetics by SKP show that despite the absence of any surface topography, chemically altered surfaces prove to have higher resistance to delamination.

Ni coatings were electrodeposited from 1:2 choline chloride (ChCl) - urea (U) deep eutectic solvents (DESs) on low carbon steel. We report on the inter-related influence of water content in the electrolyte and applied potential on the formation of Ni films and their chemical composition and morphology. This was investigated by cyclic voltammetry (CV) and chronoamperometry (CA) in combination with ex-situ characterization techniques (FE-SEM, EDS, XPS and Raman spectroscopy). Ni electrodeposition from DES is shown to be highly complex: Ni+2 reduction is followed by water reduction, which triggers electrolyte decomposition. A water content higher than 4.5 % w t and/or performing electrodeposition at potentials more negative than E =  − 0.90 V vs Ag quasi-reference electrode enhances the decomposition of the solvent. This breakdown appears via either an electrochemical reaction or triggered by water splitting. In both cases, it leads to the incorporation of DESs decomposition products, such as trimethylamine and acetaldehyde within the Ni film. Under these conditions, the films are composed of metallic Ni and NiO x (OH)2(1−x).

The presented work aims at determining the influence of surface composition and microstructure of hot dip aluminium–silicon coated steel on the formation characteristics and mechanism of a titanium-based conversion layer. Varying the amount of silicon in the molten aluminium bath changes the surface nature which in turn affects the subsequent pre-treatment process. Different phases in the layer formation process were identified in the open circuit potential evolution as a function of immersion time in the conversion solution. The homogeneity and the thickness of the conversion layer in each of these regions were evaluated using secondary electron images, Auger elemental surface maps and depth profiles. While intermetallic precipitates (FeAl3) act as nucleation centres in pure Al coatings, eutectic Si is responsible for the deposition process in a Si-rich coating. A continuous surface conversion layer is formed after 45s of immersion in the conversion bath. Also, the presence of silicon in the coating leads to the deposition of a thicker conversion layer. A model for build-up of the conversion layer is proposed based on these observations.

No abstract is provided for this article.