Publications

Sodium silicate solutions, commonly known as “water-glass”, are water-based solutions containing dissolved glass. These aqueous silicates are used for a wide variety of applications. In particular, they are commonly used in pretreatments of aluminium alloys as cleaners and corrosion inhibitors. Silicate films are known to be a promising alternative for corrosion protection and to confer high hydrophilicity to the metal surface. One of the main issues in the study of the formation of silicate films on metal oxides is the complexity of the anionic speciation in aqueous solution. The mechanism of silicate deposition on alumina is not clear yet. One of the main reasons is that it is not known how the silicate anions adsorb on the alumina surface and what type of deposition is formed on the surface. In this work, different aluminium oxides were silicate-treated by dipping in a water-based sodium silicate solution; the effect of the oxide morphology on the deposition was studied. The anionic speciation in the silicate solution was studied by means of 29 Si NMR and DLS. The morphological changes occurring on the oxide surface upon adsorption were observed by FE-SEM. WDXRF measurements allowed quantifying the deposited silicate on the porous oxide layer. The presence of silicate in the pores of the anodic layer was studied by means of GDOES. A mechanism of the deposition was proposed.

No abstract is provided for this article.

In previous work, the importance of taking the time-domain into account when studying corrosion inhibitor-containing electrochemical systems was highlighted. In this work, odd random phase electrochemical impedance spectroscopy (ORP-EIS) is applied as the electrochemical tool to study the time-effect by the evaluation of the non-stationarities per frequency decade over time for the screening of different silica- and phosphate- based corrosion inhibitors for hot-dip galvanized steel and possible corrosion inhibitor synergism. This serves as the basis for the interpretation of the results obtained from different macroscopic electrochemical techniques such as potentiodynamic polarization (PP), open circuit potential (OCP) with superimposed linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) measurements. The analysis of the time-domain shows that all systems have a system-specific 'stabilization' time which affects the interpretation of the results obtained from the macroscopic electrochemical techniques. Furthermore, these results indicate that all corrosion inhibitors tested exhibit corrosion protective action and that the combination of both silica-based corrosion inhibitors show synergistic action on hot-dip galvanized steel.

No abstract is provided for this article.

Coolant corrosion inhibitors are paramount for the durability of automotive heat exchangers. The novel generation of “hybrid coolants” consists of inorganic inhibitors added to an OAT (Organic Additive Technology) backbone. This investigation appraises the corrosion inhibition provided by OAT, phosphate and silicate (separately and combined) on AA6060 exposed to antifreeze coolant at 75 °C. The effects of hard water cations and temperature are also discussed. Linear Polarization Resistance provided a time-resolved assessment of inhibition, and potentiodynamic polarisation extrapolated the corrosion behaviour to more severe scenarios. Supported by SEM-EDX analysis, schematic diagrams of the inhibition mechanisms were elaborated for the coolant systems.

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.

This work introduces a new self-healing superhydrophobic coating based on dual actions by the corrosion inhibitor benzotriazole (BTA) and an epoxy-based shape memory polymer (SMP).

This research aims to investigate the formation mechanism of a hybrid Zr-aminosilane conversion coating as a replacement for the conventional pretreatment systems on a zinc substrate that simulates galvanization layers. This hybrid pretreatment contains both Cu and aminosilane as inorganic and organic additives. This coating has been analyzed using advanced surface analytical techniques such as XPS, EDX, FEG-AES, GDOES, and ToF-SIMS. The results showed that N is incorporated into the deposited Zr layer throughout the depth while a thin layer of aminosilane is present on the top surface. Additionally, the results obtained in this study are compared to a previous study about the same conversion system on Advanced high Strength Stainless Steel (AHSSS). This was done in order to compare the behavior of active and passive substrates in the same conversion treatment.

Electrochemical impedance spectroscopy was used as a novel technique to study gas diffusion through a surface gel. The system under study underwent an alternating current electrograining process that is used in lithography and in capacitor foils. During this process H 2 bubbles are trapped inside a gel like structure consisting of 90% water. It is presented that through in situ impedance, the gas diffusion mechanism through the gel can be explained and correlated to the pitting morphology. It is demonstrated that fast gas diffusion leads to a desired uniform aluminum pitting after alternating current processing and that the structure of the gel plays an important role in this process. Copyright © 2016 John Wiley & Sons, Ltd.

Efficient thermal management is critical to the performance and acceptance of battery electric vehicles (BEVs). In the event of coolant leakage, contact between conventional water–glycol coolants and polarized battery components may induce hydrogen evolution via electrolysis, posing a serious safety hazard. This study investigates the impact of copper corrosion inhibitors and coolant electrical conductivity on hydrogen gas formation through linear sweep voltammetry (LSV) using copper electrodes. Results indicate that commonly used corrosion inhibitors—Tolyltriazole (TTZ), Benzotriazole (BTZ), and Sodium Mercaptobenzothiazole (MBT-Na)—do not significantly reduce hydrogen evolution, even in synergistic combinations. On the other hand, lowering the coolant electrical conductivity markedly decreased hydrogen evolution, with a linear reduction in cathodic current observed in low-conductivity coolants due to the reduced ionic mobility of the electrolyte. Low-conductivity BEV coolant (86 µS/cm) presented a cathodic current density 96% lower than a high-conductivity ICE coolant (2577 µS/cm) at the same overpotential. These findings suggest that optimizing coolant conductivity is a more effective mitigation strategy than relying on corrosion inhibitor formulations.

In this work, the influence of the substrate temperature (Ts) on the chemical composition of propanethiol plasma polymers was investigated for a given set of plasma conditions. In a first study, a decrease in the atomic sulfur content (at. %S) with the deposition time (td) was observed. This behavior is explained by the heating of the growing film during deposition process, limiting the incorporation of stable sulfur-based molecules produced in the plasma. Experiments carried out by controlling the substrate temperature support this hypothesis. On the other hand, an empirical law relating the Ts and the at. %S was established. This allows for the formation of gradient layer presenting a heterogeneous chemical composition along the thickness, as determined by depth profile analysis combining X-ray photoelectron spectroscopy and C60 ion gun sputtering. The experimental data fit with the one predicted from our empiric description. The whole set of our results provide new insights in the relationship between the substrate temperature and the sulfur content in sulfur-based plasma polymers, essential for future developments.

Self-healing materials have the ability to repair themselves and recover functionality after degradation, damage and failure. This chapter reviews recent developments in self-healing protective coatings which contain rare earth-based inhibiting compounds for active corrosion protection of metals. These new ‘green’ inhibitors are being developed as substitutes for chromate-based inhibitors. Different types of organic, hybrid and metallic systems are considered, with particular emphasis on thin sol-gel based layers. The main strategies for encapsulation of RE inhibitors are also reviewed. Significant future effort is required to improve the properties of organic coatings and to explore new self-healing coating alternatives that allow controlled release of the inhibitor.