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Thin films of titanium oxide (TiO2) are synthesized at room temperature by the post-discharge of an RF atmospheric plasma torch supplied with argon and oxygen. Vapours of titanium tetraisopropoxide (TTIP) precursor are injected in the post-discharge by an argon flow rate bubbling in the liquid precursor. Without any external substrate heating, the coatings are amorphous and characterized by a thin film upon which agglomerates can be observed. The annealing of the coatings at 450°C is efficient to (partially) crystallize the TiO2 since bands characteristic of the TiO2 anatase structure are observed in Raman spectra. The films are super-hydrophilic and present excellent photocatalytic activity; two properties of particular interest for self-cleaning applications. Nevertheless, annealed coating presents a higher photocatalytic activity.

The present study investigates the effect of different conversion bath agitation and stirring conditions on the generation of Zr‐based thin film conversion coatings for steel, zinc galvanized steel, and aluminum substrates. Therefore, samples were immersed in a copper containing fluoric acid of zirconium. Film formation was monitored in situ via open circuit potential (OCP) measurements recorded during the pre‐treatment of the samples in solution. The resulting thickness and elemental distribution of the obtained Zr‐based coatings formed with and without stirring were analyzed ex situ by means of high‐resolution Auger electron spectroscopy (AES) depth profiles. Under the studied conditions, the conversion film thickness on AA6014 and cold rolled steel increased three and two times as a result of stirring. For hot dip galvanized steel, a thickness increase of 400% was achieved. The data point at mass transfer as the dominant factor for film formation. In this context, specific relations for each metal substrate type were detected.

This study investigated the deterioration of a lubricant-infused anodic aluminium oxide surface in a 1 M NaCl solution for ∼200 days. Direct observation by cryo-SEM and quantitative analyses by UV spectroscopy and EIS revealed that the long-term deterioration of the lubricant-infused surface was divided into two stages: the surface-adhered lubricant layer gradually dissolved at a constant rate until the substrate was exposed; afterwards the lubricant infused in the nanochannels began to diffuse and was depleted after ∼200 days. The EIS results also revealed that the defects reduced the corrosion resistance of the lubricant-infused surface considerably.

No abstract is provided for this article.

No abstract is provided for this article.

This paper describes a self-healing coating for corrosion protection of metals which combines two different types of self-healing mechanisms in one coating with multiple-healing functionality. 2-Mercaptobenzothiazole (MBT) was loaded into layered double hydroxide (LDH) carriers which were mixed into an acrylated polycaprolactone polyurethane based shape recovery coating and applied on Hot Dip Galvanized steel (HDG). The effect of triggered release of MBT on the protection of HDG became visible when samples with manually applied defects in the coating were immersed in 0.05 M NaCl solution (first, autonomous healing mechanism). The shape recovery (second, non-autonomous healing mechanism) was triggered by heating the samples for 2 minutes to 60°C. SEM-EDX and Raman Spectroscopy proved the presence of MBT in the LDH, in the MBT-loaded LDH in the coating and the released MBT on the HDG surface in the damaged area after being in contact with a solution containing corrosive ions. Electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET) demonstrate the corrosion protection effect of MBT in the coating with a defect and the restoration of the barrier properties of the coating after defect closure. This way, the independent mechanisms of this multi-action self-healing coating could be demonstrated.

Mg is commonly added to increase the strength of lightweight non-heat-treatable Al-Mg alloys. However these alloys become highly susceptible to grain boundary precipitation of β-Al 3 Mg 2 phase and enrichment of magnesium oxide on the metal surface induced by the alloy fabrication process and/or by the service conditions (i.e. thermal cycles). Transmission electron micrographs (TEM) of specimens sensitized at 200oC revealed elongated Mg-rich precipitates along the grain boundary line, which are preferred sites for anodic oxidation, giving rise to intergranular corrosion (IGC). Auger electron spectroscopy (AES) revealed increased yield of Mg and O, suggesting enrichment of Mg oxide on the alloy surface. Thus, the electrochemical behavior of the surface becomes affected strongly by the presence of Mg. In addition the presence of precipitates at grain boundaries also contributes to increase the number of defective areas on the protective film, giving rise to different open circuit potential (OCP) behaviors and surface morphologies for varied sensitizing conditions. Intergranular corrosion and Mg surface enrichment are discussed in the light of three main aspects: oxidation behavior and properties of the resultant oxide layer, characteristics of the grain boundaries, and grain boundary precipitation.

The goal of this article was to understand how differences in the composition and the microstructure of aluminum and aluminum-silicon coatings on steel affect the macroscopic electrochemical behavior. In particular, the focus is on the influence of the amount of silicon present in the molten aluminum bath. The electrochemical behavior is studied using electrochemical polarization experiments and is linked to the microstructure, analyzed using scanning electron microscopy-energy-dispersive x-ray (SEM-EDX) analysis. Local Volta potential differences at the metal surface are studied using scanning Kelvin probe force microscopy (SKPFM). Microstructural variations result in differences in the electrochemical behavior of the surfaces when performing full potentiodynamic scans, starting in the cathodic region. These influences, however, are not revealed as such when performing anodic and cathodic half scans, starting at open-circuit potential (OCP). Especially when first polarizing at cathodic potentials in the region of hydrogen gas evolution, significant influence of the nature of the silicon present in the aluminum coating is observed: preferential dissolution of the aluminum matrix is occurring. On this turn, this preferential dissolution leads to a shift in OCP and affects the subsequent anodic behavior. Besides, the presence of silicon also has an influence on the corrosion current density. Local potential differences are observed between the matrix and the more cathodic precipitates in the coating.

We present a combined chemical (auger electron spectroscopy) and microscopic (optical microscopy, scanning electron microscopy and scanning probe microscopy) study of the work of adhesion and delamination mechanisms at interfaces between a glassy polymer (glycol-modified polyethylene terephthalate) and Al covered with different types of surface hydroxides. A clear correlation between the measured work of adhesion and the chemical nature of the Al surface, specifically the hydroxyl coverage and the iso-electric point is found. The magnitude of the work of adhesion points to important contributions from plastic deformation in the glassy polymer for some cases. Delamination is shown to be accompanied by the formation of microscopic shear bands at such interfaces. The non-monotonous stress–strain behaviour of the glassy polymer that gives rise to the shear bands is also shown to lead to peculiar pinning events at the crack front. Evidence indicates that the occurrence of protrusions in the crack front deriving for example from the presence of stress concentrators and crack initiation sites ahead of the front, combined with mode and rate dependence of the local energy release rate along the front may pin the front at positions adjacent to a protrusion. It is believed such microscopic mode-dependent pinning phenomena may be relevant for the adhesion on patterned interfaces.

The direct ZnAl layered double hydroxide growth on AA2024 is a fast-occurring reaction, yet is characterized by an inhomogeneous film thickness. It has been shown that at the periphery of Cu-rich intermetallic, the flakes tend to be larger and denser. A combination of in situ and ex situ measurements were used to monitor the changes in the layered double hydroxide film grown on the regions of intermetallics. Immediately after immersion, an activation of the intermetallic phases is observed due to the dealloying process with an almost immediate film growth. Dealloying is followed by trenching of the adjacent Al matrix leading to an excessive production of large and dense layered double hydroxide flakes at the periphery of the intermetallic. However, the scanning electron microscopy cross-section images revealed that the trenching process leads to defects in the area surrounding the intermetallic. This could weaken the corrosion resistance performance of the layered double hydroxide conversion coating and lead to adhesion failure of consecutive polymer coatings. Nevertheless, this work highlights a few advantages and drawbacks of the layered double hydroxide conversion coatings and pathways to its potential optimization and improvement.