E. Rahimi
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26 records found
1
From electrostatics to electrochemistry
Rethinking volta potential in nowadays and future in-situ kelvin probe studies
We present a mechanically robust, cost-effective, and scalable ultra-superhydrophobic ceramic-polymer composite coating featuring a hierarchical micro/nano-structured surface. This advanced coating, fabricated via a single-step process, integrates alumina (Al2O3) and zirconia (ZrO2) to harness their individual and synergistic effects, achieving an extreme water contact angle of 180° and a sliding angle of 1°. The coating demonstrates strong adhesion and compatibility with a wide range of substrates, including aluminum and concrete. The Al2O3–ZrO2-based composite exhibits outstanding physicochemical properties, including ultra-superhydrophobicity, anti-icing, anti-corrosion, and anti-vapor condensation capabilities. It also maintains excellent non-wetting behavior across a variety of liquids. Comprehensive surface analyses, encompassing microstructural, morphological, and chemical characterization, underscore the critical role of hierarchical structuring and tailored surface chemistry in enhancing functionality. Mechanical durability assessments reveal that the coating retains its superhydrophobic performance even after extensive scratching test. Moreover, it exhibits self-cleaning, anti-adhesion, and anti-fouling characteristics, attributed to its engineered surface texture and the synergistic contributions of Al2O3–ZrO2 heterojunctions and oxide-silane bonding (Si–O–Si and Si–OH). This multifunctional ceramic-polymer coating addresses key challenges in large-scale deployment by offering a streamlined, scalable fabrication method and versatile performance, positioning it as a promising solution for diverse industrial applications.
Nickel coatings are widely used for corrosion and wear resistance, often undergoing post-treatment to enhance performance. Depending on their final application, Ni-coated steel may be subjected to mechanical forming processes to produce cylindrical can shapes, commonly used as battery cases or food storage containers where corrosion resistance is critical. Before mechanical forming, a key thermomechanical process called temper rolling is applied to improve coating adhesion, reduce residual stress, and minimize surface defects. This study systematically investigates the corrosion mechanisms of Ni-electroplated steel after annealing and temper rolling, demonstrating that both processes enhance localized corrosion resistance by modifying microstructure, surface morphology, and surface oxide evolution. These treatments promote passivity by increasing NiO content relative to Ni(OH)2, significantly improving charge transfer resistance. Additionally, iron diffusion from the steel substrate generates an electrical surface potential gradient within the coating, affecting nobility variations across different regions. Post-corrosion analysis of temper-rolled samples reveals that corrosion initiation occurs at submicron grains, where structural gaps facilitate substrate exposure, underscoring the role of processing routes in enhancing coating durability.
Advanced Nodular Thin Dense Chromium Coating
Superior Corrosion Resistance
Chromium-based functional coatings (CFCs) are widely recognized for their outstanding wear and corrosion resistance across diverse industrial sectors. However, despite advancements in deposition techniques and microstructural enhancements, many contemporary CFCs remain vulnerable to degradation in highly corrosive environments. For the first time, this research delivers a thorough characterization of the corrosion resistance of advanced CFCs, focusing on the performance of a 5 μm thin dense chromium (TDC) coating. These TDCs exhibit a distinctive, uniform nodular microstructure, characterized by approximately 3.6 μm nodules composed of defect-free near-nanocrystalline grains (227 ± 75 nm) plus enhanced electrochemical nobility. This structure promotes the rapid formation of a stable, dense bilayer oxide, resulting in a remarkably low corrosion susceptibility, effectively impeding both charge transfer and mass transport, particularly the diffusion of Cl- ions. Furthermore, the coating sustains an exceptionally high polarization resistance over extended exposure times in aqueous NaCl electrolyte. These findings offer critical insights into the design of CFCs optimized for extreme environmental durability.
The dream corrosion inhibitor would work for every substrate–environment combination, and the protection would be sustained indefinitely with an irreversible barrier layer when exposed to aggressive and changing environmental conditions. However our prior electrochemical experiments on AA2024-T3 have shown that despite the initial inhibition, all of the tested molecules had reversible bonds that limit their inhibition performance and applicability in dynamic environments, with the exception of 3-amino-1,2,4-triazole-5-thiol, which still showed 42% inhibition efficiency after being exposed to 0.1M NaCl only for three days. To our knowledge, this is the first mechanistic study that explains the origin of such quasi-sustained inhibition by an organic molecule under dynamic and aggressive conditions relevant to aerospace alloys. Potentiodynamic polarization, atomic force microscopy and scanning Kelvin probe force microscopy (AFM/SKPFM), X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS) complemented by density functional theory (DFT) calculations were used to identify the molecular mechanism responsible for the quasi-stable adsorption provided by 3-amino-1,2,4-triazole-5-thiol. Our findings suggest that a sulphatization of the Al-(hydr)oxide is the key contributor to the quasi-sustained corrosion inhibition. Sustained molecule adsorption over intermetallics in trace amounts was also observed, but their presence was insufficient to inhibit corrosion.
This research provides detailed insights into the correlation of microstructural and morphological characteristics of a Cr/CrN multilayer coating deposited onto steel and its corrosion behavior, by examining its local surface electronic properties, nanomechanical behavior, and electrochemical activity in a 3.5 % NaCl solution. A key focus of the study is the influence of physicochemical surface evolution on nano-mechanical properties of Cr/CrN coating. This is investigated by correlating electrochemical data from electrochemical impedance spectroscopy (EIS) with findings from X-ray photoelectron spectroscopy (XPS) and nanoindentation analysis. The integrated approach shed light on physicochemical evolution of the coating, and its resistance to corrosion in demanding environments.
Nanoscale corrosion analysis via in-situ surface potential mapping
Enhancing electrochemical insight with OL-EPM and AC-KPFM
Local nanoscale mapping of electrostatic surface potential (ESP) is advancing rapidly to meet the needs of electrochemistry and corrosion science. Conventional Kelvin probe force microscopy (KPFM), while valuable, is limited in liquid and dynamic redox environments due to restricted electrochemical control and spatial resolution. Recent advances in alternating current KPFM (AC-KPFM) and open-loop electric potential microscopy (OL-EPM) provide high-resolution, in-situ ESP imaging while suppressing parasitic Faradaic reactions. AC-KPFM is powerful for probing ionization and counterion interactions at solid–liquid interfaces, whereas OL-EPM enables visualization of corrosion initiation, nanoscale defects in coatings, and gradients across grain boundaries. Together, these methods bridge the gap between surface electrostatics and electrochemistry. Key challenges remain in temporal resolution, minimizing probe perturbations, and linking nanoscale data to macroscopic corrosion behavior. Nonetheless, these techniques reveal hidden electrochemical heterogeneities, clarify pathways of localized corrosion, and offer insights for designing durable, corrosion-resistant materials.
Recycling Al alloys promotes greater sustainability, as the energy required to produce recycled alloys is only about 5 % of that needed to produce the same amount of primary alloys. However, the build-up of impurities, such as Zn, during the recycling process can negatively affect the corrosion resistance of recycled alloys. The results show that the susceptibility to intergranular corrosion increased with minor additions of zinc (≤ 0.06 wt%). Zn was found to segregate along the grain boundaries, and the STEM-EDS results indicate that the Zn incorporates into the structure of Mg-Si containing grain boundary precipitates.
Chromium coatings, famed for their superior wear and corrosion resistance, are a critical component in countless industrial processes. However, the longevity of these coatings in aggressive corrosive environments continues to be a significant hurdle, even with recent advances in deposition technology and microstructural improvements. An advanced thin dense chromium (TDC) coating, with a near-nanocrystalline structure and unique morphology, naturally forms a non-conductive nano-bilayer oxide. This passive and protective layer effectively moderates electrical charge transfer, offering superior corrosion resistance. X-ray photoelectron spectroscopy (XPS) shows significant Cr3+ oxide layer formation, distinguished by multiplet splitting, after 7 days in a 0.6 M NaCl solution. The unique characteristics of this non-conductive bilayer oxide structure promote its growth and densification, leading to vertical differential charging in the O1s electron energy region. This effect arises from the enhanced resistivity of the oxide layer. Electrochemical impedance spectroscopy (EIS) confirmed these findings, showing a substantial increase in charge transfer resistance at the chromium metal/bilayer oxide interface, reaching 1.01 MΩ. Scanning Kelvin probe force microscopy (SKPFM) analysis shows that both TDC nodules and their boundaries exhibit high surface potential and work function. However, after exposure to NaCl media, these values are moderately reduced, likely due to diminished electrical surface charge distribution.
The present article investigates the influence of chemical composition and phase fractions on the corrosion behaviour of industrially produced quenching and partitioning (Q&P) martensitic stainless steels. Localised corrosion was analysed by scanning Kelvin probe force microscopy (SKPFM) and scanning electrochemical microscopy (SECM) in 3.5 wt.% NaCl solution. SKPFM revealed a Volta-potential difference of around 40 mV between inclusions and the matrix, which is larger than the Volta potential variations within the matrix. This difference in surface potential is a driving force for selective dissolution (corrosion initiation) at inclusions and inclusion/matrix interfaces. SECM detected early pitting initiation, particularly in alloys containing MnS and TiN inclusions. Results suggest that pitting initiation and propagation occur at those specific regions. This study emphasised that irrespective of chemical composition and phase fraction, localised corrosion initiation in Q&P-processed martensitic stainless steels is predominantly governed by the presence of inclusions.
The authors regret that an error occurred in the description of equation 3 in the published version of the above-mentioned article, which should be as follows: [Formula presented] The correct equation was implemented for calculating all the results presented in the article, so all results, discussions and conclusions presented in the manuscript remain fully valid > The authors would like to apologise for any inconvenience caused.
Carbon materials possess active sites and functionalities on the surface that can attract prominent interest as solid adsorbents for diverse gas adsorption. This study aimed to predict the optimized methane uptake, adsorption energy (Ead), and adsorbent rediscovery through multitechniques of neural, regression, classifier ML-DFT, and Uniform Manifold Approximation and Projection (UMAP). Nitrogen and oxygen (N/O) functionalities and graphene, graphene oxide (GO), and N-doped GO were applied to the methane storage medium. Multi-ML algorithms were employed for the adsorption energy of CH4 uptake on (i) N/O functionalities such as pyridinic (N-py), carboxyl (O-II), oxidized (N-x), hydroxyl (O-h), Nitroso (N-ni), and Amine (primary, secondary, and tertiary). (ii) The graphene surfaces are decorated with N/O heteroatoms to construct graphene oxide (GO) and N-doped GO. The DFT calculations were applied by PW91 and the Dmol3 package. N/O-functionalities in the distance of ∼2.0 to 3.1 Å groups obtained Ead of approximately −2.0 to −4 eV. Further, ML models accomplished the forthcoming rediscovery of CH4 physisorption by using the multiadsorptive features of optimized adsorbents with an R2 of 0.99. ML-derived sensitivity analysis approach was applied to specifications such as deformation adsorption energy, N/O functionality type, and optimized structure. CH4 adsorption specifications indicate sensitivity levels of −0.03 to 0.02 eV. The synergetic DFT/ML approaches distinguished the modeled and rediscovered phases of CH4 adsorption on N/O functional groups and graphene structures. UMAP is employed as a new adsorbent screening approach to play a complementary role in the ML modeling process.
This paper presents a novel approach to investigate atmospheric corrosion kinetics of carbon steel under multi-droplet conditions. A homemade climate chamber has been developed to accurately control and monitor environmental conditions, including temperature (T) and relative humidity (RH), during exposure. Carbon steel corrosion kinetics are monitored with a custom-designed Electrical Resistance (ER) sensor pair. Savitzky-Golay (S-G) based filtering technique has been used for the corrosion signal processing. In parallel, top-view droplet temporal evolution has been recorded by microscopic imaging and analyzed for both droplet size distribution and the solid-liquid contact angle. The droplet size distribution can typically be described with a power-law form curve. The curve shows a decrease in height and a concurrent expansion in width with progressive drying. The introduction of NaCl into the electrolyte and surface roughness variations have also been identified to substantially influence the carbon steel corrosion rate. A strong correlation between the corrosion rate derived from the ER monitoring method and the RH can be observed. This correlation is further analyzed to incorporate the impact of droplet-based electrolyte conditions. This study offers valuable insights into the development of mechanistic and kinetic prediction models for atmospheric corrosion.
The biodegradation of therapeutic magnetic-oxide nanoparticles (MONPs) in the human body raises concerns about their lifespan, functionality, and health risks. Interactions between apoferritin proteins and MONPs in the spleen, liver, and inflammatory macrophages significantly accelerate nanoparticle degradation, releasing metal ions taken up by apoferritin. This can alter the protein’s biological structure and properties, potentially causing health hazards. This study examines changes in apoferritin’s shape, electrical surface potential (ESP), and protein-core composition after incubation with cobalt-ferrite (CoFe2O4) oxide nanoparticles. Using atomic force microscopy (AFM) and scanning Kelvin probe force microscopy (SKPFM), we observed changes in the topography and ESP distribution in apoferritin nanofilms over time. After 48 h, the characteristic apoferritin hole (∼1.35 nm) vanished, and the protein’s height increased from ∼3.5 to ∼7.5 nm due to hole filling. This resulted in a significant ESP increase on the filled-apoferritin surface, attributed to the formation of a heterogeneous chemical composition and crystal structure (γ-Fe2O3, Fe3O4, CoO, CoOOH, FeOOH, and Co3O4). These changes enhance electrostatic interactions and surface charge between the protein and the AFM tip. This approach aids in predicting and improving the MONP lifespan while reducing their toxicity and preventing apoferritin deformation and dysfunction.
Atmospheric corrosion of iron under a single droplet
A new systematic multi-electrochemical approach
Utilizing a dedicated micro-sized three-electrode cell, this study systematically investigates early-stage electrochemical properties and corrosion behavior of pure iron under single droplets. Various volumes and NaCl concentrations were considered during the evaporation-driven shape and concentration evolution of single droplets. The measurements disclosed that reducing the droplet size from 5 µL to 1.5 µL at 0.01 M NaCl concentration, increased noise resistance (Rn) and polarization resistance (Rp) values. However, at 0.1 M and 0.2 M NaCl concentrations, reducing droplet size led to the domination of relatively high chloride ion concentration over oxygen diffusion, resulting in a very low Rn and Rp and hence enhanced localized corrosion.