| 1. |
- Chen, Dihao, et al.
(author)
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Correlation between pitting susceptibility and surface acidity, point of zero charge of passive film on aluminum: Influence of alloying elements
- 2024
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In: Corrosion Science. - : Elsevier BV. - 0010-938X .- 1879-0496. ; 227
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Journal article (peer-reviewed)abstract
- The pitting potential, intrinsic surface acidity, point of zero charge of passive film on Al are studied using first-principles calculations to establish their relationships. Influences of alloying elements Zn, Cr, Nb, Si, Mo and Sc on adsorption of NH3 and NaCl, pHpzc of Al2O3 and pitting susceptibility of Al are investigated. The efficiency for enhancing pitting resistance of Al is evaluated, yielding the ratios Si: Zn: Cr: Mo: Nb: Sc = 1.8: − 0.3: 1: 1.9: 1.4: 0.2. A model for the dependence of pitting potential on the concentration of alloying elements in Al alloy matrix is developed, based on effects of alloying elements on the surface charge of passive film. The effects of Sc on pitting potential and pHpzc of Al oxide are predicted based on the calculated results, which are supported by electrochemical measurement, XPS analysis and contact angle titration.
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| 2. |
- Larsson, Alfred, et al.
(author)
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Dynamics of early-stage oxide formation on a Ni-Cr-Mo alloy
- 2024
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In: NPJ MATERIALS DEGRADATION. - : Springer Nature. - 2397-2106. ; 8:1
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Journal article (peer-reviewed)abstract
- Corrosion results in large costs and environmental impact but can be controlled by thin oxide films that passivate the metal surfaces and hinder further oxidation or dissolution in an aqueous environment. The structure, chemistry, and thickness of these oxide films play a significant role in determining their anti-corrosion properties and the early-stage oxidation dynamics affect the properties of the developed oxide. Here, we use in situ X-ray Photoelectron Spectroscopy (XPS) to study the early-stage oxidation of a Ni-Cr-Mo alloy at room temperature and up to 400 degrees C. Cr and Mo begin to oxidize immediately after exposure to O2, and Cr3+, Mo4+, and Mo6+ oxides are formed. In contrast, Ni does not contribute significantly to the oxide film. A self-limiting oxide thickness, which did not depend on temperature below 400 degrees C, is observed. This is attributed to the consumption of available Cr and Mo near the surface, which results in an enrichment of metallic Ni under the oxide. The self-limited oxide thickness is 6-8 angstrom, which corresponds to 3-4 atomic layers of cations in the oxide. At 400 degrees C, sublimation of Mo6+ oxide is observed, resulting in the formation of an almost pure layer of Cr2O3 on the alloy surface. Lastly, a mechanism is presented that explains the formation of the bi-layer oxide structure observed for Ni-Cr-Mo alloys, which involves the enhanced migration of hexavalent Mo ions in the electric field, which drives mass transport during oxidation according to both the Cabrera Mott model and the Point Defect Model.
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| 3. |
- Larsson, Alfred, et al.
(author)
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In situ quantitative analysis of electrochemical oxide film development on metal surfaces using ambient pressure X-ray photoelectron spectroscopy : Industrial alloys
- 2023
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In: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 611
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Journal article (peer-reviewed)abstract
- Ambient Pressure X-ray Photoelectron Spectroscopy combined with an electrochemical setup is used to study, in situ, the electrochemical oxide growth on an in-dustrial Ni-Cr-Mo alloy. The native oxide film was characterized in vacuum and in water vapor at 17 mbar, and was found to be 11.4 & ANGS; thick and rich in Cr3+. In 0.1 M NaCl electrolyte, anodic growth of the oxide film at potentials up to 700 mV vs Ag/AgCl nearly doubled the thickness of the oxide film. Moreover, a transformation of the oxide composition occurred, as the oxide became enriched in Mo6+ with a chemical fingerprint more like that of pure MoO3. Both thermodynamics and kinetics of the oxidation of the alloying elements dictate the oxide film growth and composition. Furthermore, we develop the quantitative analysis of oxide composition and thickness to take into account the attenuation through the liquid water and the water vapor atmosphere. Finally, we discuss the differences between ex situ, UHV, in situ, and operando measurements. Our approach is robust, fast, simple, and suitable for systematically probing metal surfaces after aqueous exposure and electro-chemical polarization, which promises wide applications for studies of solid-liquid interfaces in corrosion, batteries, fuel cells, and electrocatalysis.
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| 4. |
- Larsson, Alfred, et al.
(author)
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The Oxygen Evolution Reaction Drives Passivity Breakdown for Ni–Cr–Mo Alloys
- 2023
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In: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 35:39
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Journal article (peer-reviewed)abstract
- Corrosion is the main factor limiting the lifetime of metallic materials, and a fundamental understanding of the governing mechanism and surface processes is difficult to achieve since the thin oxide films at the metal–liquid interface governing passivity are notoriously challenging to study. In this work, a combination of synchrotron-based techniques and electrochemical methods is used to investigate the passive film breakdown of a Ni–Cr–Mo alloy, which is used in many industrial applications. This alloy is found to be active toward oxygen evolution reaction (OER), and the OER onset coincides with the loss of passivity and severe metal dissolution. The OER mechanism involves the oxidation of Mo4+ sites in the oxide film to Mo6+ that can be dissolved, which results in passivity breakdown. This is fundamentally different from typical transpassive breakdown of Cr-containing alloys where Cr6+ is postulated to be dissolved at high anodic potentials, which is not observed here. At high current densities, OER also leads to acidification of the solution near the surface, further triggering metal dissolution. The OER plays an important role in the mechanism of passivity breakdown of Ni–Cr–Mo alloys due to their catalytic activity, and this effect needs to be considered when studying the corrosion of catalytically active alloys.
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| 5. |
- Li, Cheng, et al.
(author)
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Introducing water factors improves simulations of maize stomatal conductance models under plastic film mulching in arid and semi-arid irrigation areas
- 2023
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In: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 617
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Journal article (peer-reviewed)abstract
- Plastic film mulching (PFM) in the cropland may alter biophysical conditions for crop growth, which may not be accounted for in existing stomatal conductance models. This can affect the accuracy of carbon–nitrogen-water cycle simulations for the soil-crop systems and hamper our understanding of internal mechanisms that control plant leaf stomatal conductance (gsw). To evaluate the simulations of PFM effects on gsw, the three models (i.e., Ball-Woodrow-Berry (BWB), Ball-Berry-Leuning (BBL), and unified stomatal optimization (USO) models) were used. The two model modification factors were leaf-air temperature difference (ΔT) and a water response function (f(θ)). A two-year maize (Zea mays L.) field experiment was conducted under different PFM (black, transparent, and no-mulch). The performance of the BWB model was poor under varying water status in the arid irrigation area. As for the BBL and USO models, the coefficient of determination and modified efficiency coefficient of the modified models increased 5.8%–90.6% and 6.5%–145.4%, respectively, compared with the initial models. The root mean square error and relative error of the modified models decreased 3.5%–67.9% and 4.8%–65.6%, respectively. The ΔT and f(θ) factors effectively improved the BBL and USO models, but the f(θ)-modified models performed better than ΔT-modified models under PFM. Overall, our results suggest that the maize land implemented with plastic film mulching has altered biophysical conditions, leading to significant changes in crop photosynthesis, leaf-air temperature difference and top-soil water conditions. Accurate estimates of stomatal conductance require the model to consider water response functions and leaf-air temperature difference, particularly in environmental conditions associated with different extents of water deficit or drought.
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| 6. |
- Li, Cheng, et al.
(author)
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Ridge planting with transparent plastic mulching improves maize productivity by regulating the distribution and utilization of soil water, heat, and canopy radiation in arid irrigation area
- 2023
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In: Agricultural Water Management. - : Elsevier BV. - 0378-3774. ; 280
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Journal article (peer-reviewed)abstract
- Ridge-furrow mulching system is widely used for improving soil hydrothermal conditions and crop productivity in semiarid and arid rainfed areas. The response of crop productivity to resource capture and utilization is crucial for agricultural field management and sustainable development. However, few have simultaneously investigated the coupling effect of plastic film mulching (PM) types and planting patterns on root and shoot growth, photosynthesis, yield, resource capture and utilization as well as their potential links in the same experiment, especially in arid irrigation areas, limiting our understanding of PM and ridge planting application. This study conducted a two-year field experiment with four treatments: 1) flat planting with transparent plastic film mulch (FT); 2) flat planting with black plastic film mulch (FB); 3) ridge–furrow planting with transparent plastic film mulch (RT); 4) ridge–furrow planting with black plastic film mulch (RB). The results showed that RT significantly increased soil water storage and root growth at the silking and grain-filling stages in both years by enhancing soil thermal time with 151.9–176.2 °C d and the intercepted photosynthetic active radiation with 22.2–57.4 MJ m–2. In addition, RT had a significantly higher net photosynthetic rate than FT and FB at the 12-leaf and silking stages, enhancing the transportation of stem and leaf to grain. The logistic equation using growing degree days as the independent variable characterized the dynamic features of maize growth under different PM types (transparent or black) coupled with ridge–furrow planting. RT accelerated dry matter accumulation by enhancing the maximum growth rate and extending the rapid growth period, resulting in 12.9–15.2 % more dry matter accumulation and 10.0–16.7 % higher grain yields than FB. Furthermore, RT significantly increased resource use efficiencies by 10.1–17.3 % for water, 3.0–5.5 % for thermal, and 4.0–9.1 % for radiation compared with FB. Ridge planting had the highest contributor rates, with >40 % for yield and resource capture. This study suggests that RT maintains high maize productivity and resource use efficiencies in arid irrigation areas with limited water resources by regulating soil water, heat, and canopy radiation distribution and utilization.
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| 7. |
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| 8. |
- Ratia-Hanby, V., et al.
(author)
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Characterization of surface films that develop on pre-oxidized copper in anoxic simulated groundwater with sulphide
- 2023
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In: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 676
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Journal article (peer-reviewed)abstract
- Surface films formed on pre-oxidized copper in anoxic simulated groundwater with sulphide were characterized by field emission gun scanning electron microscopy (FEG-SEM), Fourier transform infrared spectroscopy (FT-IR), open circuit potential (OCP) measurements, and via analysing the water chemistry and weight changes in the specimens. Additionally, films developed under identical conditions on pre-oxidized and ground copper specimens were characterized by glow discharge optical emission spectroscopy (GDOES). The results revealed that the sulphide content in the groundwater significantly influences the morphology, composition and thickness of the surface film. The build-up of Cu2S was evidenced at the sulphide contents of 32 mg/L and 320 mg/L. GDOES depth profiling revealed that sulphur and oxygen coexisted in the film all through its thickness, yet the surface was essentially rich in sulphur. The results from characterization are presented in detail in this paper and discussed from the perspective of capabilities of the used methods.
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| 9. |
- Wang, Di, et al.
(author)
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Enhancing adhesion and durability: A biomimetic approach with dopamine-modified lignin-polydimethylsiloxane coatings
- 2024
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In: Corrosion Science. - : Elsevier Ltd. - 0010-938X .- 1879-0496. ; 236
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Journal article (peer-reviewed)abstract
- Corrosion causes significant challenges in industrial settings, leading to economic losses and safety concerns. Previously, we developed a lignin-polydimethylsiloxane (lignin-PDMS) coating that exhibited high corrosion resistance. However, the adhesion of the developed lignin-PDMS coating to carbon steel was limited, affecting its overall performance. To address this, we incorporated dopamine (DOPA), known for its strong adhesive properties, as a pre-treatment before applying the coating. It was found that the adhesion and corrosion resistance of lignin-PDMS coated steel could be improved by adjusting the pH value of the DOPA solution. The steel treated with pH 4.5 DOPA solution showed two times higher adhesion strength to the coating than non-treated steel. After the DOPA treatment, the coating can maintain high barrier property for at least 3 months in 1 M NaCl solution, which is even better than commercial gelcoat, demonstrating super corrosion protection. Quartz Crystal Microbalance with Dissipation (QCM-D) and X-ray Photoelectron Spectroscopy (XPS) analyses confirmed the DOPA deposition on the steel surface. Our findings show that the DOPA-lignin-PDMS system is an environmentally friendly and efficient solution for enhancing the durability of steels in corrosive environments.
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| 10. |
- Yue, Xiaoqi, et al.
(author)
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Effect of hydrogen on the passivation for ultra-thin 316 L SS foil
- 2023
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In: NPJ MATERIALS DEGRADATION. - : Springer Nature. - 2397-2106. ; 7:1
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Journal article (peer-reviewed)abstract
- The reformation and characterisation of the passive film formed on ultra-thin 316 L after hydrogen charging is investigated by combining EBSD, TMDS, XRD, Synchrotron-based XPS, and electrochemical experiments. The results show that ultra-thin foil reforms a passive film after 12 h of hydrogen release in NaCl solution. The reformed passive film is half the thickness of the as-received passive film and is dominated by Cr oxides/hydroxides. The lattice extension caused by residual hydrogen accelerates Cr migration to form Cr2O3; while the diffusible hydrogen occupies the cation vacancies and results in high defect density for the reformed passive film within 12 h.
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