npj Materials Degradation最新文献

Understanding the dissolution and passivation of iron in aqueous environments is essential for enhancing its corrosion resistance and expanding its applications. We present Thermo-Kinetic (TK) diagrams for iron in deaerated solutions with no added sodium sulfate (Na₂SO₄) and with 0.1 M Na₂SO₄ over the pH range 1-14, constructed by integrating current density contours from potentiodynamic polarization with thermodynamic E-pH diagrams. TK diagrams indicate that in solutions with no added Na₂SO₄, iron passivates above pH 7, with a minimum passive current density (i_p) of 5 ×10^-6 mA·cm^-2 at pH 8. The addition of 0.1 M Na₂SO₄ delayed passivation until pH 12 and increased i_p nearly tenfold. Galvanostatic (GS) polarization and EIS validated the TK diagram results. XPS after GS polarization revealed an FeOOH/Fe₂O₃ film at pH 10, while Fe₃O₄/Fe₂O₃ dominated at pH 12 and 14. These results clarify how sulfate compromises iron passivity and highlight TK diagrams as a powerful tool for mapping corrosion behavior.

This work aims to develop multilayer coating systems to enhance the long-term corrosion performance of aluminium-based components. The systems consists of a high-performance ceramic matrix that provides physical barrier protection, and a topcoat layer containing encapsulated Ce-based inhibitors, offering active corrosion protection through controlled released mechanisms. Two types of nanoparticles were used for the encapsulation, zeolite and halloysite nanotubes, each with different release triggers and kinetics. Multifunctional coatings demonstrated a superior corrosion performance compared to the passive unmodified coatings. Inhibitor release from the nanoparticles was triggered by ionic exchange processes and changes in pH associated with corrosion activity.

In radioactive waste repositories, cement is used for construction, backfill, and waste encapsulation. Over time, cracks may form, creating potential pathways for contaminant migration. A self-sealing mechanism is through calcium carbonate (CaCO₃) precipitation, which can be driven by microbial oxidation of organic compounds. We explored microbially induced calcite precipitation facilitated by metabolism of citrate, a complexant in low- and intermediate- level radioactive waste (L/ILW). Nitrate-reducing microcosms containing cement pellets, citrate, nitrate, alkaline sediment inoculum, and synthetic groundwater (pH 11.2) were incubated in the dark (20 °C, 40 days). Aqueous geochemical data revealed complete citrate removal, denitrification, pH decrease to pH 9, and removal of Ca²⁺ _(aq). Furthermore, 16S rRNA gene sequencing showed enrichment of citrate-oxidising/nitrate-reducing bacteria. Solid phase analysis (XRD, SEM-EDS, µXCT) confirmed new calcite precipitates reduced cement porosity and sealed cracks at the surface. Overall, microbial oxidation of organic ligands under alkaline conditions may reduce contaminant mobility in L/ILW repositories through calcite precipitation and crack sealing.

Polydimethylsiloxane (PDMS) is a synthetic elastomer widely used in biomedical and industrial applications. Despite its widespread use, the natural evolution of its mechanical and surface properties over time remains poorly understood. In this study, we fabricated PDMS samples with base-to-curing agent mixing ratios from 5:1 to 30:1 and aged them for up to 8 weeks under six non-harsh conditions at room temperature. Contact angle measurements revealed increasing hydrophobicity with aging, with maximum increases up to 16.5°. Mechanical testing showed up to 130% increases in Young's modulus and 60% changes in flexibility after 5 weeks. Storage in mineral oil best preserved surface hydrophilicity, while storage in water best maintained mechanical integrity. These results provide a framework for optimizing PDMS storage conditions in microfluidic and biomedical device applications.

The mechanisms of 2-mercaptobenzothiazole (2-MBT) adsorption and corrosion inhibition on the aerospace AA2024 T3 aluminium alloy have been investigated using electrochemistry and advanced surface analyses. Electrochemical methods were used to measure the degree of corrosion protection in neutral chloride media, while advanced surface analysis techniques were employed to determine the interfacial interaction and inhibitor action mechanisms. It is shown that 2-MBT effectively inhibits corrosion of the alloy, reducing its susceptibility to corrosion attack and its corrosion rate. Surface analysis, including the use of ToF-SIMS 3-D chemical mapping, confirms 2-MBT adsorption on partially dealloyed intermetallic particles (IMPs) along with the presence of a thin 2-MBT layer on the top-most alloy surface. Chloride ions breakdown the native oxide film, allowing 2-MBT to adsorb on IMPs, thereby inhibiting further localized corrosion on these particles, while the 2-MBT layer on the surface protects the alloy matrix from surface oxidation.

Bolted flanged joints are essential for connecting piping and process equipment but are vulnerable to localized corrosion that leads to sudden, unpredictable leaks. Electrochemical noise (EN) measurements can detect such corrosion, yet processing EN data is time-consuming and requires expertise. This study applies recurrent neural networks (RNNs) to automate corrosion type identification on flange surfaces using raw EN signals from spontaneous electrochemical reactions. In this work, supervised, hybrid, and unsupervised ML approaches are evaluated using experimentally obtained EN data. Among supervised models, the long short-term memory (LSTM) model achieves 93.62% accuracy. A hybrid method combining LSTM autoencoder features with a random forest classifier improves accuracy to 97.85%. An unsupervised method using LSTM autoencoder, principal component analysis, and k-means clustering also shows strong potential for real-time corrosion monitoring. Automated identification of corrosion types on flanged joints supports more effective material protection strategies, reducing the risk of failure in critical infrastructure.

The effect of hydrogen charging during plastic deformation was investigated on a ferritic steel containing TiC nano-precipitates. Specimens were subjected to a slow strain rate tensile test (SSRT) up to 0, 1, or 3% plastic engineering strain, held until a total duration of 2 h to saturate with hydrogen, then fast fractured. The specimens pre-strained elastically absorbed 2.36 wppm of hydrogen, which increased to 3.69 wppm for 3% plastic strain. Only 0.72 wppm is stored in non-dislocation traps such as precipitates, grain boundaries, and lattice sites, which makes dislocations the main contributor to hydrogen trapping. The increased hydrogen uptake did not lead to a decrease in fracture strain, which remained between 6 and 10% for all pre-strains, compared to 60% for full SSRT tests that were charged for a shorter time. This research highlights the necessity of high plastic strains and the presence of hydrogen in the environment during crack growth to cause HE in ductile steels.

The collapse of reinforced autoclaved aerated concrete (RAAC) panels has attracted considerable public and academic interest. As detailed experimental data are not yet available and replicating the natural corrosion process requires years or decades, computational modelling is essential to understand under which conditions corrosion remains concealed. The very high porosity of RAAC is widely suspected to be a major contributing factor. However, current corrosion-induced cracking models are known to struggle with capturing the role of concrete porosity. To remedy this critical deficiency, we propose to enrich corrosion-induced cracking modelling with the analytical solution of reactive transport equations governing the precipitation of rust and a porosity-dependent description of diffusivity. With this, the corrosion concealment in RAAC panels is studied computationally for the first time, revealing that RAAC panels can suddenly collapse before any warning of corrosion-induced surface cracking and allowing to map the conditions most likely to result in sudden collapse.

Microbial interactions with mineral surfaces play a critical role in biogeochemical cycles, yet their dynamic coupling with mineral reactivity remains poorly constrained. Here, in-situ time-resolved monitoring of topographic evolution of the calcite-bacteria interface was performed using a fluid cell coupled to vertical scanning interferometry (VSI). The cyanobacterial strain Chroococcidiopsis thermalis PCC 7203 was inoculated onto polished and pre-etched calcite surfaces under conditions strongly undersaturated or closer to calcite saturation. The formation of localized topographic highs, produced by dissolution of surrounding material, was found to correlate with the residence time of attached cells at Ω = 0.0, but not at Ω = 0.3. Physiological tests suggested that the composition of the bulk fluid modulates microbial activity, thereby influencing interfacial pH, and in turn, calcite reactivity. Moreover, calcite reactivity was found to exert a stronger control on bacterial detachment dynamics than initial surface roughness or surface charge under the tested conditions. These findings emphasize the importance of microscale feedbacks between microbial colonization and mineral weathering, and demonstrate the potential of in-situ interferometric imaging for probing the dynamics of processes at microbe-mineral interfaces.

The effect of water chemistry, surface condition, alkalizing agent (LiOH vs. KOH), and Zn addition was investigated at 300 °C on the oxidation behaviour of reduced activation ferritic martensitic (RAF/M) EUROFER-97. EUROFER-97 is the proposed material for the water-cooled lithium lead breeder blanket (WCLL-BB) section of DEMO, but its behaviour under elevated temperature hydrogenated water has never been investigated. Advanced material characterization showed that, despite its relatively low chromium content, EUROFER-97 exhibits high corrosion resistance. This is because EUROFER-97 is protected by an inner polycrystalline FeCr₂O₄ layer, formed regardless of the water chemistry and surface preparation investigated. The outer non-protective oxide consists of Fe₃O₄ crystallites, which were refined when KOH was used. When injected, Zn was observed only on top of the outer crystallites without diffusing into the inner oxide layer. These findings demonstrate the excellent oxidation behaviour of EUROFER-97 in the proposed water chemistry, highlighting its suitability for the WCLL-BB section.