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The erosion-corrosion mechanism in rotary flowing seawater is hugely complicated due to the multiscale coupling processes of particle-surface impact, ion mass transfer, and interface electrochemistry. Therefore, developing erosion-corrosion resistant material and exploring the synergistic mechanism between sand erosion and electrochemical corrosion is vital. This study conducted the erosion-corrosion test on Ni2FeCrMo0.2 high-entropy alloy under the particle-seawater flow. Based on a coupled analysis of multi-component weight loss, electrochemical behavior, and microscopic damage morphology, the multiscale coupling processes of sand transportation, particle-surface impact, ion mass transfer, and interface electrochemistry were revealed. The present study found that with the increase of sand size, the energy carried by the particles promoted impact erosion. Additionally, particle movement enhanced ion mass transfer through turbulent effects, and the impact behavior disrupted the passivation film to promote electrochemical processes by reducing the thickness of the passivation film, leading to an increase in the erosion-corrosion rate. However, when the particle size continued to increase to a certain extent, the impact frequency decreased, reducing the erosion-corrosion rate. As the sand size grew, the dominant damage mechanism transitioned from pure corrosion (100 μm) to synergistic effects (200 μm, 400 μm) and then to pure erosion (800 μm). This study provides an in-depth understanding of the erosion-corrosion mechanism in seawater from the perspective of particle-ion-fluid-surface interaction by multi-element characterization.

Nowadays, a good corrosion resistance of lightweight steel is demanded for its application. However, due to the high contents of Mn and C, which are always corrosion-susceptible elements in steels, the conventional lightweight steel is not desirable for this mission. Although Cr is widely believed to be a common alloying element to improve the corrosion resistance of most steels, it is considered to be ineligible using in the lightweight steel due to the relatively high content of C. This is because the trade-off between corrosion resistance and mechanical properties by alloying Cr. In recent years, the rapid developments of additive and coating manufacturing have provided new possibilities for both the Cr alloying and microstructural modulation to improve corrosion resistance of lightweight steel. In this case, to design a certain chemical composition using in additive and coating manufacturing, it is interesting to clarify the effects of Cr alloying on the corrosion resistance of lightweight steel. To reveal it, in the present work, the Fe–Mn–Al–Cr–Si–Mo–C lightweight steel alloyed with Cr contents of 4 wt%, 8 wt% and 12 wt% are prepared. The corrosion resistances and mechanisms of Cr-alloyed lightweight steels in 3.5 wt% NaCl solution are investigated by electrochemical and immersion tests. The present work may provide new insights for the composition design of lightweight steel, especially for the directions of additive and coating manufacturing.

Chemical conversion coating (CCC) is a cost-effective and industrially scalable technique to tackle the issue of corrosion of Magnesium and its alloys, crucial for reducing global greenhouse gas emissions by the road transportation sector. Amongst all the possible CCCs, the phosphate conversion coating (PCC) has one of the highest industrial application potential. This article demonstrates limitations in the traditional understanding of Mg-PCC mechanism, primarily dictated by increased local pH near the Mg-substrate leading to double deprotonation of phosphoric acid (H3PO4 → H2PO4− + H+; H2PO4− → HPO42− + H+). The HPO42− further reacts to Mg2+ and subsequent supersaturation of precipitate, MgHPO4.3H2O results in the coating formation. The new hypothesis proposed for Mg-PCC is based on the argument that the second deprotonation reaction is energetically unfavorable, instead, the reaction is mostly limited to the first deprotonation of the phosphoric acid resulting in H2PO4−. This H2PO4− reacts to the Mg2+ and forms an intermediate complex ion, (Mg2+-H2PO4−)+. The Mg substrate, when exposed to an aqueous environment, releases Mg2+, resulting in a negatively charged substrate. The complex (Mg2+-H2PO4−)+ ions are electrostatically attracted to the negatively charged substrate resulting in the reaction responsible for MHPT (MgHPO4.3H2O) coating. This new hypothesis is supported by thermodynamic calculations through density functional theory (DFT) and experiments.

To assess the corrosion resistance of Cu-Fe deformation in situ alloys in a chloride ion environment, Cu-Fe alloys with varying Fe contents (5 wt%, 10 wt%, and 14 wt%) were prepared using vacuum induction melting, and the impact of Fe content on the corrosion resistance was examined. The corrosion morphology and corrosion products were analyzed, and the corrosion rate, corrosion period, dynamic potential polarization curves, electrochemical parameters, and electrochemical impedance spectra with different Fe contents were determined. However, the corrosion resistance of Cu-Fe alloys initially increased with an increase in Fe content before decreasing, with Cu-10 wt% Fe alloys (95% reduction rate) exhibiting the best corrosion resistance. As the Fe content increased, the amount of primary Fe phase gradually increased and became more densely distributed. This led to an increase in the dense oxide film on the surface, thereby enhancing the corrosion resistance of the material. Moreover, with a further increase in Fe, the primary Fe phase exhibited coarsening and non-uniform distribution. This resulted in the oxide film becoming looser, leading to a decreased corrosion resistance of the alloy.

In this research, corrosion behavior and discharge capabilities of the AZ61-In alloy experiencing hot rolling process have been discussed in detail. The results reveal that the introduction of indium to magnesium facilitates the dissolution of magnesium by augmenting a quantity of secondary phases, generating less-protective products. The corrosion resistance of AZI plus 50 % rolling reduction is improved attributed to the preferred basal orientation and further recrystallization. Moreover, the average discharge potentials of AZI-50 % can respectively reach −1.551 V and −1.234 V at 10 mA cm−2 and 50 mA cm−2, showing potential for application in seawater activated batteries.

In this study, a novel type of green and highly efficient Na-CDs corrosion inhibitor was successfully prepared using a hydrothermal method, and its properties were thoroughly characterized. The results revealed that the Na-CDs possessed a uniform nanoscale size distribution and a well-defined graphene lattice structure. The corrosion inhibition performance of Na-CDs at varying concentrations was assessed, and it was found that the corrosion inhibition efficiency initially increased with the increase of concentration, peaking at over 96 % when the concentration reached 150 mg/L, before subsequently declining. Analysis of the adsorption behavior of Na-CDs on the metal surface confirmed that the adsorption process followed the R-P adsorption isotherm, indicative of an almost ideal homogeneous monolayer adsorption. The corrosion inhibition mechanism is the result of forming a protective film on the metal surface by physical adsorption and chemical adsorption, with the bridging role of Cl- further reinforcing the structure of this film. However, at excessively high concentrations of Na-CDs, desorption occurred, compromising the integrity of the protective film. This study enriches the field of metal-doped carbon dots as corrosion inhibitors and provides insights into the synthesis of carbon dots and the development of carbon dot-based corrosion inhibitors.

Corrosion inhibitors play a vital role in impeding the corrosion process of steel bars within concrete structures exposed to corrosive environments. Nevertheless, conventional corrosion inhibitors pose environmental risks. In contrast, contemporary studies have explored corrosion inhibitors that are eco-friendly. However, these inhibitors are burdened by high costs and complex production processes, impeding the widespread application in concrete structures. Consequently, this study presents an innovative solution by incorporating uniconazole, an agricultural fungicide, as a corrosion inhibitor for steel bars in concrete structures. The steel bars were exposed to corrosion within a simulated concrete pore solution containing 0.6 mol/L NaCl, both with and without the presence of uniconazole. The morphology and hydrophilicity of the steel bar surface were investigated via optical microscope and contact angle experiments. Electrochemical tests (open circuit potential, potentiodynamic polarization, electrochemical impedance spectroscopy, and Mott-Schottky analysis) and X-ray photoelectron spectroscopy were employed to investigate the corrosion inhibition performance and mechanism of uniconazole. The results demonstrate that uniconazole elevates the hydrophobicity and contributes to the corrosion inhibition of steel bars. Electrochemical test results indicate that as the concentration of uniconazole increases from 1 × 10−4 mol/L to 1 × 10−3 mol/L, the inhibition efficiency likewise demonstrates a corresponding increase, escalating from around 50 %–90 %. Uniconazole molecules function as mixed-type inhibitors, exhibiting characteristics of both anode-type and cathode-type inhibitors. The adsorption of uniconazole enhances the stability and thickness of the passive-adsorbed layer on the steel surface, effectively impeding the charge transfer process and obstructing the interaction of corrosive substances with the base metal. In summary, the application of uniconazole exhibits the highlights of efficient, cost-effective, environmentally friendly, and the potential for scalable production. This positions uniconazole as a promising candidate for use as a corrosion inhibitor in the domain of concrete structures.

Microcrack damage repair and microbial contamination prevention are two major challenges for anti-corrosion coatings on the surfaces of underwater installations. In this study, water-triggered self-healing microcapsules were combined with low-surface-energy fluoropolymers to prepare a bifunctional anti-corrosion coating with underwater self-healing and bio-fouling properties. The results showed that the prepared microcapsules had good mechanical, thermal, and environmental stability, with an average diameter of 153 μm and an encapsulation rate of 66.7%. When the microcapsule content in the coating was 8 wt%, the microcapsule dispersion performance and healing barrier effect of the composite coating were optimal, and the repair efficiency reached 81.6%. Furthermore, compared with the coating without microcapsules or graft fluoropolymers (PFG), the sample denoted as PFG18/4/IPDI-MC/ER showed the largest surface water contact angle and had the best protein inhibition rate of 87% when using bovine hemoglobin to detect the protein adsorption concentration on the coating surface.

An effective and biodegradable Ficus tikoua leaves extract was studied as a corrosion inhibitor for carbon steel in hydrochloric acid. Systematic electrochemical experiments and morphological characterization were carried out to investigate the properties of the corrosion inhibitor. Meanwhile, quantum chemical calculations were performed to aid further understanding of the electrochemical mechanism. The electrochemical results reveal that the extract inhibitors act as a mixed-type with an inhibition efficiency up to 95.8% at 298 K. Moreover, this extract shows good inhibory activity at a wide range of temperatures and the corresponding results were further confirmed by morphological analysis. The chemical formulae of these major components are fully optimized in the DFT with B3LYP in the gas phase and the base set is 6-311++G (d, p)., (Copyright © 2019 Elsevier B.V. All rights reserved.)