The increasing deployment of offshore infrastructure has raised concerns about the environmental impact of corrosion protection systems, particularly galvanic anodes, which release trace metals such as zinc and aluminium into the marine environment. Traditional monitoring methods often fail to capture the bioavailable fraction of these contaminants or provide adequate temporal resolution. Here, we investigate the brown macroalga Saccharina latissima as a bioindicator of metal emissions from galvanic anodes. Laboratory and mesocosm experiments demonstrated linear relationships between environmental concentrations and metal accumulation, particularly for zinc. Compared to grab and passive sampling, S. latissima provided more consistent and representative exposure estimates. These findings highlight the potential of S. latissima as a cost-effective and reliable bioindicator for offshore trace metal contamination monitoring and its integration into environmental assessment frameworks.
Understanding the long-term degradation of Ti-6Al-4V under oxidative conditions is essential for studying microstructurally selective corrosion in biomedical alloys, yet quantitative, time-resolved methods to track selective phase dissolution remain limited. This study investigates the corrosion behavior of Ti-6Al-4V exposed to phosphate-buffered saline (PBS) containing 1 M H2O2 for up to 10 days, with a particular focus on quantifying the progression of /3-phase dissolution and on developing an in situ electrochemical impedance spectroscopy (EIS)-based methodology to monitor dissolution depth over time. EIS, open-circuit potential (OCP) monitoring, and time-lapse microscopy were combined with equivalent circuit modeling (ECM) and finite element modeling (FEM). Immediately after H2O2 addition, the polarization resistance dropped sharply. Microscopy revealed selective dissolution of the /3-phase, progressing uniformly to depths of several tens of micrometers, while the a-phase remained largely unaffected. Dissolution continued steadily at an average rate of 0.23 mu m/h. EIS spectra exhibited a de Levie-type impedance feature directly linked to dissolution depth, in agreement with FEM and ECM analyses. In addition, one-dimensional finite element modeling elucidated the time evolution of the resistive contributions to the EIS response. A phenomenological model was established to predict the propagation of /3-phase dissolution based on EIS data, exploiting a quantitative relationship between EIS-derived relative capacitance and the exposed a-phase surface area observed by time-lapse microscopy. While the applied peroxide concentration exceeds physiological levels, the methodology presented here enables non-destructive, time-resolved monitoring of corrosion progression and is directly transferable to longer-term studies employing more realistic simulated inflammatory conditions.
The role of interfacial water in adhesion performance was investigated for coil-coated hot-dip galavanised steel pretreated with TiZr-based conversion layers, with and without an adhesion promoter. The polymer coating was a polyester/melamine system. Laboratory-prepared Zn model surfaces were used to perform in situ spectroscopic investigation of the metal/polymer interface. A multi-scale approach combining electrochemical impedance spectroscopy (EIS), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), electron probe microanalysis (EPMA), X-ray fluorescence (XRF), and in situ ATR-FTIR spectroscopy in the Kretschmann geometry was employed to correlate macroscopic electrochemical behavior with nanoscale interfacial processes. Water uptake was estimated between 0.5 to 0.8 vol.% independently of the surface pretreatment and regardless of the presence of the topcoat. The topcoat provided effective barrier properties independent of the surface pretreatment. When only the primer was applied, differences appeared. EIS analysis revealed earlier adhesion loss and/or corrosion initiation in absence of the adhesion promotor. In situ ATR-FTIR analysis and optical simulations of the IR spectra showed greater interfacial liquid-like water accumulation for TiZr, accompanied by early formation of Zn(OH)2 species. Surface analyses showed that the presence of the adhesion promoter led to a more uniform Ti distribution, reducing Ti-deficient regions. These results demonstrated that the adhesion promoter improved coating performance by stabilizing the metal/polymer interface and by limiting interfacial water accumulation. This work established a robust multi-scale methodology for probing interfacial processes in coil-coated systems.
The Erichsen cupping test is widely used to evaluate formability and adhesion of coil-coated materials, as it produces strains comparable to industrial forming. In the present work, a hot-dip galvanized steel with a polyester/melamine primer and topcoat was selected. Mechanical deformations were applied using a spherical indenter at penetration depths of 1-6 mm. Coating thickness along the deformation profile was measured on cross-sections by optical microscope. The effective contact area of the coating with the electrolyte in the electrochemical cell was determined by 3D scanning. Electrochemical impedance spectroscopy in a 0.5 M NaCl solution over 72 h was used to assess water uptake and anticorrosion performance, following methodologies developed in previous studies. The influence of coating thickness and effective contact area on the EIS-calculated water uptake was examined. A deformation threshold (>= 5 mm) was identified, above which blister initiation was strongly accelerated. Failure mechanisms such as cracks in the Zn layer and loss of coating adhesion leading to blistering were characterized using electrochemical measurements and post-mortem SEM-EDS observations. The approach provides relevant dielectric and electrochemical markers for understanding how mechanical deformation influences water uptake and failure in coil-coatings.
Advanced high-strength steels exhibit sensitivity to diffusible hydrogen content, mainly observed during tensile testing. Although the initial yield stress and ultimate tensile strength are not significantly affected, ductility decreases with increasing hydrogen content. This sensitivity to diffusible hydrogen depends on strain rate and stress concentrations. This study examines the influence of diffusible hydrogen content on the ductile fracture of DP780GI steel, in the form of 1 mm thick sheets. Samples were prepared with specific geometries, with notches and holes, to study different mechanical states, and fracture tests were performed to evaluate ductility as a function of hydrogen content and stress triaxiality. The local strain rate was around 1 × 10−4 s−1, which is lower than the value used in industrial applications, to enhance the hydrogen sensitivity. A hydrogen charging process was used, including zinc coating removal, electrochemical loading, and electrolytic deposition of a zinc layer to prevent hydrogen desorption. The hydrogen content was measured by thermal desorption analysis after the mechanical testing. It is observed that the maximum local elongation decreases with increasing hydrogen content, with a noticeable effect above 0.25 ppm. Cracks form in areas of maximum effective deformation, and their location varies depending on the geometry of the sample and the hydrogen content. The evolution of the maximum effective strain before fracture shows a significant decrease in ductility with increasing hydrogen content, regardless of the mechanical state.
