Corrosion Conditions Research Articles

Anticorrosion and rheological properties of Calyptocarpus vialis extract as a green coating for mild steel in 2MH2SO4

This study assesses the rheological properties and corrosion inhibition efficacy of Calyptocarpus vialis (CV) extract, a wild plant in Asteraceae family. Shear and dynamic rheology studies show that CV extract has shear-thinning behaviour, with viscosity changes occurring at higher shear rates, most likely owing to aggregate formation. These aggregates may develop due to certain solvent characteristics and a jamming tendency is due to the presence of extract phytochemicals. Dynamic rheology confirms its viscoelastic nature. Corrosion inhibition effectiveness was investigated using Mild Steel (MS) in 2 M H2SO4, resulting in an 82.69 % inhibition with an extract concentration of 1 g/L. Adsorption isotherm indicates phytochemical adsorption on MS surface. Contact angles of polished MS (87.30°), with extract (80.10°), and without extract (51.25°) show decrease in wetting and increase in hydrophobicity which indicates that a thin protective layer is formed at MS surface. FE-SEM (Field Emission Scanning Electron Microscopy) images reveal that the CV extract forms a protective barrier on the MS surface, significantly reducing corrosion as compared to the unprotected surface exposed to the mild acid solution. Theoretical calculations, including Density Functional Theory (DFT) simulations, Monte Carlo (MC), and Molecular Dynamics (MD) simulations, support the experimental findings, elucidating phytochemicals adsorption on the MS surface. Further research is required to examine the scalability of CV extracts for industrial applications, as well as their long-term stability and efficacy in various corrosive conditions.

Highly thermally conductive and anti-corrosive silicone grease enabled using unique hexagonal boron nitride nanosheet/alumina microsphere-based hierarchical structure for heat dissipation in a humid environment

Electronic devices operating in the marine environment often face severe corrosion. In addition, highly integrated and powerful devices generate a notable amount of heat, which may lead to a deterioration in performance and reliability. Therefore, it is essential to develop thermal interface materials (TIMs) with high thermal conductivity and outstanding corrosion resistance for efficient and stable heat dissipation. Herein, a novel hierarchical three-dimensional structure comprising hexagonal boron nitride sheet wrapped alumina microsphere/hexagonal boron nitride flakes (Al2O3@BNNS-BNFs) has been fabricated, which can simultaneously improve the thermal conductivity and corrosion resistance of silicone grease (SG). The dispersibility of BNFs in SG is enhanced by the uniform distribution of Al2O3@BNNSs, while the BNNSs attached to the surface of Al2O3 microspheres improves the compatibility of BNFs and Al2O3 microspheres, thereby effectively enhancing the thermal conductivity of SGs. The thermal conductivity of the Al2O3@BNNS-BNFs/SG can reach up to 1.98 W/(m·K) when the content of Al2O3@BNNS-BNFs is 20 wt%, which is ∼13 times that of ordinary SG. Meanwhile, the Al2O3@BNNS-BNFs/SGs also demonstrate excellent electrical insulation (1.50 × 1013 Ω cm) and corrosion resistance compared to some commercial products. Furthermore, subsequent tests indicate that the Al2O3@BNNS-BNFs/SGs can effectively dissipate heat for electronic devices in various humid environments. These unique properties make the Al2O3@BNNS-BNFs/SGs promising as multifunctional TIMs for thermal management in complex environments, especially in humid or corrosive conditions.

Numerical Investigation on Cathodic Protection of X80 Pipeline Steel in Marine Environment

Abstract Submarine pipelines are usually buried in sea mud, but part of the pipes will be exposed to seawater directly because of the change of seabed, the differences between sea mud and seawater result in different corrosion states. Generally, due to its large geometric size, complex medium, difficult to detect and other reasons, corrosion defects will cause greater harm to pipeline materials. A numerical analysis model of the outer surface corrosion of submarine pipelines was developed to simulate status of cathodic protection, furthermore, potential distribution and local density of current inside the defects was also analyzed and evaluated. The results indicates that: (1)The CP potential distributes more evenly in sea mud when the same sacrificial anode is used, and the cathodic protection current density needed to meet the anti-corrosion requirements is much larger in seawater than in sea mud.(2)Compared with sea mud, the polarization potential of the sacrificial anode in seawater is more negative, and the CP potential at the edge of anodes is the most positive in both sea mud and seawater. Furthermore, in seawater, the dissolution rate of sacrificial anodes closer to the seabed is lower, and anodes dissolve much faster at the inner surface, while it is just the opposite in sea mud.(3)Cathodic protection cannot ensure complete and effective protection at defect points. At defect bottom, the cathodic protection current is partially shielded, reducing the effectiveness of CP system on corrosion protection of pipelines. Moreover, the shielding effect of defect point on cathodic protection current has a great deal with the geometric shape of defect points, with decreasing width and increasing depth, the shielding phenomenon becomes more obvious.(4) Numerical simulation technique based on the finite element model provides a new method to solve this problem and plays a positive role in assessing anti-corrosion status and the service life of anodes.

Corrosion behavior of novel Ti6422 alloy with equiaxed structure and lamellar structure in HCl solution

This study systematically investigated the electrochemical corrosion and static immersion corrosion behavior of the novel Ti6422 (Ti-6Al-4V-2Mo-2Fe) alloy with equiaxed (EM) and lamellar structure (LM) in HCl solution. The differences in corrosion performance between EM and LM samples were analyzed based on the characteristics of the passive film and substrate microstructure. Results indicated that the LM sample contained higher contents of TiO₂, Al₂O₃, and MoO₃ with higher stability compared with the EM sample, and the thickness of passive film was approximately twice that of the EM sample. Additionally, the donor density of LM sample was lower than EM sample. These findings indicate that the passive film on LM samples is thicker, with fewer defects and higher density. Electrochemical corrosion results revealed that the corrosion current of LM samples was lower and the polarization resistance was higher than these of EM samples, both suggesting superior corrosion resistance of LM samples. Immersion corrosion further confirmed that the LM sample had a lower corrosion rate. The enhanced corrosion resistance in LM samples was primarily due to higher content of corrosion-resistant β phase. Conversely, the numerous micro-galvanic cells between αs precipitates and adjacent β phase in EM samples weakened the corrosion resistance. Overall, these results demonstrated that regulating microstructure through heat treatment is an effective strategy for improving corrosion resistance of titanium alloys.

Effect of Y2O3 content on the corrosion behavior of Cu-10W composites prepared by spark plasma sintering

Cu-W composites with good mechanical properties, electrical properties and corrosion resistance are still rare. In this study, Y2O3 reinforced Cu-10W composites were prepared by spark plasma sintering. The effects of different Y2O3 contents on the corrosion resistance of Cu-10W composites were studied by static immersion corrosion and electrochemical corrosion. The results show that, the incorporation of Y2O3 makes the microstructure of Cu-10W composites dense and grain refinement. The minimum weight loss value can be obtained when Y2O3 content is 2 wt%. Y2O3 can effectively increase the self-corrosion potential and corrosion current density of Cu-10W composites and enhance the electrochemical impedance level. And Y2O3 can increase the resistivity ring radius, which leads to the increase of charge transfer resistance Rct and the decrease of Warburg impedance Zw.

Electrochemical activation of Pt electrode for efficient and stable anion exchange membrane ammonia electrolyzer

Replacing the oxygen evolution reaction in water electrolysis with ammonia oxidation reaction enables low voltage hydrogen production. Pt is a promising catalyst for the ammonia oxidation reaction due to its superior dehydrogenation and low affinity for *N, but Nads poisoning deactivates the Pt surface. This study proposes a method to improve ammonia oxidation performance and stability through electrochemical activation, introducing cathodic corrosion and recovery conditions. The half-cell results showed a peak current density of 74.2 mA cm−2 and retention ratio of 17 %. Adjusting the lower and upper cell voltage in a membrane electrode assembly based single cell optimized surface cleaning and inhibits further poisoning by O/OHads above 0.75 Vcell. Furthermore, incorporation of recovery conditions can enhance the stability of poisoned electrode compared to that in chronoamperometry test. The results of pulsed ammonia electrolysis tests incorporating recovery conditions suggested a novel approach to practical hydrogen production by stabilizing catalysts with a 83 % Faradaic efficiency at 0.1 A cm−2

Microstructures, physical and corrosion behavior of NiCoFeCu high-entropy alloy nanocomposite coatings electro-co-deposited with nano-Si3N4 particles

High-entropy alloys (HEAs) have gained increasing attention over the decades, owing to their distinctive properties. Electrodeposition stands out as a cost-effective and convenient method for producing diverse types of HEAs. However, there's little attention paid to fabricating ceramic-enhanced HEA composites. In this study, NiFeCoCu/Si3N4 HEA nanocomposites were electro-co-deposited in an aqueous solution with varying loadings of Si3N4 nanoparticles and current densities. The morphological, elemental, and phase-structure characteristics were investigated using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) techniques. The Vickers-microhardness measurements, reciprocal wear, and electrochemical tests were conducted to evaluate the physical and anti-corrosion performance of the composite coatings. The findings indicate that the incorporation of Si3N4 nanoparticles not only changes the surface morphologies, compositions, and textures of the HEA matrix but also significantly enhances both the wear and anti-corrosion performance in artificial water by refining the microstructures and reducing the defects of the composite coatings. The HEA-3 g/L-Si3N4-40 mA/cm2 and HEA-6 g/L-Si3N4-40 mA/cm2 composite coatings demonstrate the best wear performance and anti-corrosion properties among the samples investigated, respectively. The present study shows a significant improvement in the mechanical and anti-corrosion properties of HEA coatings by incorporation of Si3N4 nanoparticles, which is a very promising approach for the surface protection of engineering materials used in corrosive and frictional-working conditions.

Irreversible, in situ, self-healing and self-glazing of geopolymers

Geopolymers are the result of the reaction of alkaline activators with reactive aluminosilicates. By dissolving these aluminosilicates and undergoing processes of polycondensation and geopolymerization, they form robust structures with distinct properties compared to other ceramics. These non-crystalline materials exhibit notable resistance to corrosion, heat, and environmental conditions, such as changes in pressure and temperature. Consequently, geopolymers, e.g., of stoichiometric composition (M2O•Al2O3•4SiO2•11H2O (or 13H2O)), find a place between cement and ceramics regarding mechanical properties. Considering the formulation of geopolymer blends, this study demonstrates that these materials have self-healing and self-glazing properties under high-temperature conditions. Through systematic experimentation and considering the specific properties of sodium-based (Na-GP) and potassium-based (K-GP) geopolymers, a combination of sodium and potassium waterglass compounds with different weight percentages were used to achieve geopolymer materials with optimum self-healing and self-glazing properties. Moreover, these samples were subjected to heat treatment under various time and temperature conditions to optimize their properties in terms of crystallization, and the best results were reported from among these variables. Based on the findings, the specific combination consisting of 75 wt% sodium waterglass and 25 wt% potassium waterglass were the best mixtures. This mixture was heated at a rate of 5 °C per minute to a temperature of 1000 °C and held isothermally for 6 h before being cooled at the same rate. As a result, an amorphous geopolymer turned into a ceramic with irreversible, self-healing, and self-glazing capabilities.

Enhanced thermal insulation and corrosion resistance in Ni-Fe cermet through incorporation of high-entropy spinel oxides

The influence of high-entropy spinel oxide (HESO) content on the microstructure, electrical conductivity, and high-temperature corrosion resistance of HESO/NiFe cermets were investigated. The results found that the addition of 10 to 30wt.% HESO enhanced sintering densification and thermal insulation, although it also resulted in reduced electrical conductivity. Isothermal oxidation tests conducted at 900 °C for 10hours revealed that cermets containing 30 to 50wt.% HESO exhibited significantly lower weight gains (0.954 to 1.167mgcm⁻²) and oxidation rate constants (0.1057 to 0.1525mg² cm⁻⁴ h⁻¹). Furthermore, static corrosion tests in AlF₃-KF-Al₂O₃ molten salt demonstrated that HESO effectively mitigated the erosion of the metallic phase by the fluoride molten salt. This study holds significant potential by providing new insights for the design of inert anodes for aluminum electrolysis and exploring the practical applications of high-entropy oxide materials.

Analysis of Corrosion Causes and Optimization of Corrosion Evaluation Methods for Water Injection System in Changqing JY Oilfield

Abstract Based on the corrosion characteristics of the water injection system in Changqing Oilfield, an experimental study was conducted on the corrosion of the water injection system caused by carbon dioxide, hydrogen sulfide, bacteria, and water treatment agents in the produced liquid. The main influencing factors of corrosion in the water injection system were analyzed, and it was clarified that the corrosion of the water injection system in Changqing Oilfield was mainly caused by oxygen corrosion, which also had an impact on the water quality of the injection. Combining static corrosion analysis with the introduction of pitting and dynamic corrosion rate testing methods, the average corrosion rate of JY oilfield water injection system has a positive correlation with pitting corrosion, while the average corrosion rate of clean water has a stronger correlation with pitting corrosion. The corrosion evaluation method has been optimized, providing technical basis for formulating effective anti-corrosion measures for the oilfield.

Technology Focus: Artificial Lift (October 2024)

Summer blockbuster season has passed, but it’s always nice to grab a bucket of popcorn and escape reality with a movie. Some movies even teach lessons—as in, sometimes it takes hard work and incremental improvements to advance. Chugging raw eggs, sprinting steps, and boxing meat slabs in epic training montages can be effective (Rocky), but so can optimization with computational flow dynamics. Paper IPTC 24243 shows that redesign of a jet pump sliding-sleeve coupling can considerably reduce pressure losses and increase throughput. The scientific method can even be exciting. Who doesn’t enjoy hypothesizing, experimenting, measuring, cleaning records, analyzing, and scaling up—especially if it pays off with a huge computer-generated explosion in the desert (Oppenheimer)? Paper SPE 218124 demonstrates the benefits of digitizing and analyzing operational data from electrical submersible pumps (ESPs) to improve run life and profitability. Paper OTC 34898 describes a comprehensive testing program to qualify load-bearing ESP deployment cable for corrosive conditions. Sometimes an overly precise plan draws us to the edge of our seats. The protagonist has recruited a crew of experts, rehearsed obsessively, ensured that every loose end has been tied, and yet some unknown still (temporarily) derails the vault raid (Ocean’s Eleven). Paper SPE 218028 attempts to bypass chance and minimize production interference by orchestrating a network of intermittently gas lifted wells. Is physics limiting what you can do? Then change the rules. You could move existence into a computer simulation (The Matrix) or perhaps start over with a novel material. Paper IPTC 23949 introduces fiber-reinforced thermoplastic sucker rods to accomplish more with less. Who doesn’t enjoy a quality sequel? There must be an infinite number of things that can be jumped with a car (The Fast and the Furious). Paper SPE 215010 analyzes failures of gas lift valves retrieved from subsea wells and could be considered a follow-up to paper OTC 30943, an artificial lift paper featured in 2021. Closure also can satisfy, even if it’s just the final act for a high school chemistry teacher with a side gig (Breaking Bad). With that in mind, it’s been an honor and a pleasure to pen the Artificial Lift Technology Focus page these past few years. I look forward to seeing who the directors cast next for this character. Recommended additional reading at OnePetro: www.onepetro.org. SPE 218124 Digitalizing the Management of Electric Submersible Pump Failures Through Failure Prevention and Post-Mortem Analysis Tools by Michael Ellsworth, Suncor Energy, et al. SPE 218028 Optimization of Gas-Injection Network Using Genetic Algorithm: A Solution for Intermittent Gas Lift Wells by Ankit Garg, Oil and Natural Gas Corporation, et al. IPTC 24243 Increasing Oil Production With Jet Pumps by Reducing Pressure Losses in the Jet Pump/Sliding Sleeve Coupling by J. Soria, Sertecpet, et al.

Lateral impact performance of pitting corroded CFST columns for offshore applications

This study investigates the lateral impact performance of circular concrete-filled steel tube (CFST) columns with pitting corrosion. A comprehensive set of 15 CFST specimens was meticulously constructed, including 3 non-corroded specimens used as controls and 12 specimens subjected to varying pitting corrosion conditions. These conditions included different depths, numbers of corrosion pits, and pitting corrosion distributions. Additionally, an extensive Finite Element Analysis (FEA) was conducted to gain detailed insights into the instantaneous dynamic responses of CFST columns with pitting corrosion under lateral impact. The FEA included failure mechanism investigation, stress and strain analyses, bending moment responses, strain rate changes, and energy transformations. The experimental and FEA results reveal that pitting corrosion significantly affects the dynamic behavior of CFST columns, demonstrating reductions in impact force and flexural capacity due to pitting corrosion, and highlighting the influence of corrosion depth, number of pits, and distribution on column behavior. Finally, a simplified model incorporating the effects of pitting corrosion was proposed to estimate the dynamic flexural strength of pitting corroded CFST columns. The results provide valuable insights for designing and assessing the structural integrity of CFST members in marine environments.

The investigation of support effect from hard substrate to soft coating of PI/EP-PTFE under different coating thicknesses and frictional contacts

Engine bearings on ships can experience rapid failure under extreme conditions, such as when seawater infiltrates the engine compartment due to collisions with reefs or missile attacks. To enhance the self-lubrication and wear resistance of these bearings, a composite coating consisting of ZrO2-PI/EP-PTFE has been designed. This coating was applied using liquid spraying technology onto the surfaces of A370 aluminum alloy, CuPb22Sn2.5 copper alloy, and 15# carbon steel. Three different coating thicknesses—20 μm, 30 μm, and 40 μm—were applied to each substrate. The tribological properties of these coatings on the three substrates were investigated under both dry sliding wear and seawater corrosion conditions. The results indicated that the tribological performance of the coatings is influenced by factors such as the coating hardness, frictional contacts, and the supporting effect of the substrate. The hardness and elastic modulus of the coatings decreased as the coating thickness increased. A thicker coating results in reduced support from the substrate. The adhesive wear of these coatings under dry sliding wear conditions on the different substrates is also presented. The coefficients of friction (CoFs) of these coatings increased with coating thickness on all three substrates. In contrast, the wear rates decreased as the coating thickness increased. The hardness of the coating was influenced by the support effect of the substrate. The primary factors governing the tribological performance of the coating under dry sliding conditions are the pinch action of the hard grinding ball against the soft coating on the hard substrate and the contact pressure. Abrasive wear, spalling wear, plough grooves, and spalling pits were observed under seawater corrosion conditions. These findings suggest that increased coating thickness is associated with lower coefficients of friction (CoFs) and wear rates. The main contributing factors are seawater corrosion and the scouring effect of high-frequency reciprocating friction.

Study Evaluates Long-Term Corrosion Risk of Load-Bearing, High-Power ESP Cable

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 34898, “Long-Term Corrosion-Risk Evaluation of Load-Bearing, High-Power Electrical Submersible Pump Cable,” by Serko A. Sarian, SPE, Alkhorayef Petroleum, and Hattan Banjar, SPE, and Chidirim Ejim, SPE, Saudi Aramco, et al. The paper has not been peer reviewed. Copyright 2024 Offshore Technology Conference. _ In this study, a fit-for-purpose electrical submersible pump (ESP) load-bearing power cable was deployed inside the production tubing of a sour oil well for an extended period of service. Project economics required the power-cable metallurgy to survive long-term exposure reliably for up to 15% hydrogen sulfide (H2S) and high-salinity production fluids. Laboratory tests simulating varying sour well and extended galvanic corrosion conditions have been performed to determine the adequacy of the selected armor metallurgy in downhole corrosive environments. Introduction In recent years, various types of load-bearing power cable-deployed ESP (CDESP) systems have been introduced, eliminating the need to install or remove a conventional ESP along with the completion and reducing ESP changeover time by more than 80%. More recently, live-well CDESP systems have been developed and tested to eliminate the need for a well-kill operation. The most-critical and costly component of such a system is the load-bearing power cable. The cable has the dual purpose of conveyance and long-term powering-up of the ESP. In a conventional artificial lift operation, the ESP is conveyed using the production tubing with a non-load-bearing power cable strapped to the outside of the tubing. This operation requires a workover rig to remove and reinstall the entire completion and a killed-well operation that might permanently damage the reservoir. The main advantages of a CDESP system include operational efficiency gain and cost reduction, no reservoir skin damage, and production-loss minimization. However, a few challenges exist with the use of CDESP. These cables must have significantly different structures from commercial oil and gas power cables. These differences are detailed in the complete paper. Cable-Design Requirements CDESP system criteria include multiple-year continued service in adverse oilwell and reservoir conditions such as sour fluids, high gas/oil ratios (GOR) and temperatures, and abrasion caused by solids production. The following product acceptance requirements were set in advance: - Three redeployments or retrievals after the initial deployment - Single deployment continued runtime to meet or exceed the regional conventional ESP system runtime Based on regional statistics, a conventional ESP system single-deployment average run time is 2.5 years. The effective CDESP power-cable service life target then becomes 2.5 years × four total deployments = 10 years, which served as the basis for all cable-associated testing and reliability metrics.

Insight into the effect of ultrasonic treatment on surface properties and flotation behavior of chalcopyrite after galvanic corrosion of grinding media and chalcopyrite

Ultrasonic treatment is an effective means to promote chalcopyrite flotation. Chalcopyrite needs to be grinded before flotation production. During the grinding process, galvanic corrosion occurs between chalcopyrite and iron grinding media. Galvanic corrosion significantly affects the efficacy of ultrasonic treatment on chalcopyrite flotation. Nonetheless, there is still a lack of research on ultrasonic treatment of chalcopyrite after galvanic corrosion. In this study, micro-flotation tests, SEM-EDS, TOF-SIMS, XPS, ICP-OES and electrochemical tests were used to study the effects of ultrasonic treatment on the surface properties and flotation behavior of chalcopyrite before and after galvanic corrosion under different ultrasonic conditions and galvanic corrosion conditions. The results show that in the absence of galvanic corrosion, short time and low power ultrasonic treatment can improve chalcopyrite floatability. However, when the chalcopyrite after strong galvanic corrosion is subjected to ultrasonic treatment, the increase of galvanic corrosion temperature, galvanic corrosion time, ultrasound power and ultrasound time result in a marked reduction of the flotation recovery of chalcopyrite. The synergistic effect of ultrasonic and galvanic corrosion significantly inhibits the flotation recovery of chalcopyrite, which may provide a new potential way for the inhibition of sulfide ore in flotation production. The research results are helpful to expand the use range of ultrasonic processing for sulfide mineral pretreatment and flotation, and provide a theoretical reference for the application of ultrasonic treatment in sulfide minerals with galvanic corrosion.

Catechol/m-Phenylenediamine Modified Sol-Gel Coating with Enhanced Long-Lasting Anticorrosion Performance on 3003 Al Alloy.

Aluminum alloys, characterized by their low density and high mechanical strength, are widely applied in the manufacturing sector. However, the application of aluminum alloys in extreme environments presents severe corrosion challenges. Sol-gel organic coating techniques have garnered significant attention due to their excellent stability, barrier properties, and cost-effectiveness, as well as their simpler processing. Nevertheless, conventional sol-gel coatings are unable to withstand the corrosive effects of high-chloride and high-halide ion environments such as marine conditions, owing to their inherent structural defects. Therefore, this study proposes the utilization of a simple method to synthesize catechol (CA) and meta-phenylenediamine (MPD)-derived catecholamine compounds to modify sol-gel coatings. Surface characteristics of the modified coatings were analyzed using Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The thickness of the modified coating was approximately 6.8 μm. The CA/MPD-modified substance effectively densifies the sol-gel coating, enhancing its corrosion protection performance. A 3.5 wt% NaCl solution was used to simulate a marine environment, and electrochemical impedance spectroscopy (EIS) was conducted using an electrochemical workstation to evaluate the coating's protective properties over a long-term period. The results indicate that the modified coating provides protection for 3003 aluminum alloy for a minimum of 30 days under corrosive conditions, outperforming unmodified sol-gel coatings in terms of corrosion resistance.

Enhanced high-temperature corrosion resistance of Cr-modified phosphate/aluminum powder composite coatings: Mechanisms and thermodynamic insights

Phosphate composite coatings are regarded as one of the tangible solutions for surface protection in salt spray environments, benefiting from their cost-effectiveness and prominent structure stability upon high-temperature exposure. However, rapid curing of these coatings often leads to crack formation, and the underlying corrosion mechanisms in service conditions remain insufficiently understood, limiting their practical applications. In this study, we developed chromium-incorporated phosphate/aluminum powder composite (Cr-P/Al) coatings and evaluated their corrosion resistance under alternating conditions of salt spray corrosion and oxidation at 450 °C. By integrating experimental results, ab initio calculations, and thermodynamic analysis, we demonstrate that the incorporation of Cr significantly enhances the performance of the P/Al coatings. The structural evolution was first revealed that Cr’s modification reduced tensile stress and prevented cracks in the coating. A mixed layer of amorphous oxides and phosphates forms on the surface of the Al powder, providing robust binding strength. A novel corrosion mechanism was identified that Cl2 and volatile chlorides facilitated the removal of Cl-. This process is more ineffective with Cr-P/Al coating, as amorphous Cr oxide has low reactivity at a high log[p(Cl2)] and low log[p(O2)] compared with amorphous Mg and Fe oxide, thereby enhancing the corrosion resistance of the coating. These coating densification methods and corrosion protection mechanisms provide a critical foundation for the future application of phosphate composite coatings.

Stress corrosion cracking performance of LPBF-built 316L stainless steel post-processed with heat treatment and severe shot peening

ABSTRACT This study investigated stress corrosion cracking (SCC) susceptibility in laser powder bed fusion (LPBF) printed 316L stainless steel under corrosive conditions. LPBF process inherently introduces residual stresses and surface defects that can compromise material integrity in aggressive environments. Post-processing techniques, specifically severe shot peening (SSP), heat treatments at 600°C and 900°C, and their combinations were employed to mitigate these issues. SCC testing in a boiling 25% NaCl solution assessed cracking over a period of five weeks. The results demonstrate that while SSP initially introduced compressive residual stresses potentially enhancing SCC resistance, subsequent mechanical deformation by U-bending diminished these benefits, leading to increased susceptibility to cracking. Tensile stresses induced by U-bending appeared to override the benefits of defect closure and reduced surface roughness, resulting in cracking. Notably, only specimens subjected to AB + SSP and HT600 + SSP conditions exhibited cracking during the testing period, highlighting the complex interplay between residual stresses, mechanical deformation, and SCC behaviour.

Corrosion of stainless steel and molybdenum used as PCC in Na//Sb-Bi liquid metal batteries under cycling conditions

Material compatibility is a major challenge in the development of liquid metal batteries. In this study, the corrosion behavior of two candidate positive current collector materials, austenitic stainless steel and molybdenum, in Na//SbBi9 liquid metal batteries is investigated. In-situ corrosion in operating cells is compared with static corrosion in SbBi9 (corresponding to the fully charged state) and Na0.30Sb0.07Bi0.63 (representing the fully discharged state) at 450 °C. Stainless steel shows a much better corrosion resistance in Na-Sb-Bi alloy (corrosion depth below 1 μm after 750 h static exposure) than in SbBi9 (7–9 μm corrosion layer) thanks to the formation of a thin oxide layer. The corrosion under cycling conditions shows similar characteristics (formation of solid Fe-Cr-Ni-Sb compounds), though accelerated, as static exposure to SbBi9. Molybdenum exhibits a very good corrosion resistance both in static and in cycling conditions, showing merely a minor dissolution into the adjacent alloy.

The role of electrode potential in CaCO3 scaling on steel surfaces under cathodic and corrosion conditions

The role of electrode potential in CaCO3 scaling behavior and kinetics on carbon steel and stainless steel surfaces is investigated through electrochemical tests, surface characterization, and numerical modeling. Under cathodic conditions, calcite is the dominant CaCO3 polymorph, its lateral growth on steel surfaces follows exponential kinetics. However, under gradually promoted corrosion conditions of carbon steel, the presence of corrosion products induces more aragonite deposition and inhibits the lateral growth of CaCO3 scale, gradually evolving from exponential to linear kinetics. This work provides further insight into how the cathodic and anodic reactions of steel corrosion respectively promote and inhibit CaCO3 scaling.