Corrosive Ions Research Articles

A novel arrangement of active and ultra-stable electrocatalyst based on iron/nickel/cobalt oxy/hydroxides for continuous oxygen evolution from alkaline seawater splitting

This research offers novel ideas for development a new class of materials with enhanced OER kinetics utilizing an easy electrochemical deposition technique. Here, the Ti/CoNiyOx/FeOOH electrocatalyst was prepared in two steps. First, CoNiyOx thin film was anodically electrodeposited on an activated titanium substrate. Then iron oxyhydroxide (FeOOH) nanosheets were cathodically electrodeposited on the first layer. The properties of this electrocatalyst was evaluated and compared with some monolayer electrocatalysts using field emission scanning electron microscopy (FE-SEM), Raman, energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical methods. The Ti/CoNiyOx/FeOOH electrode requires an overpotential less than 330 mV at 100 mA/cm2 with Tafel constant of only 23.7 mV/dec for OER. The Ti/CoNiyOx/FeOOH electrode delivered long-term electrochemical stability in a solution containing corrosive chloride ions for more than 90 h at a constant current density of 100 mA/cm2 (with less than 9 % potential increase). Overall seawater splitting using the synthesized Ti/CoNiyOx/FeOOH electrode was performed at a current density of 100 mA/cm2 by a voltage as low as 1.58 V. The exceptional activity was ascribed to the synergistic effects of high electrochemical active sites and appropriate charge transfer ability found in CoNiyOx/FeOOH junction.

Research on the Chloride Ion Corrosion Resistance of Cu-Sb-Added Low-Carbon Steel

The corrosion resistance of low-carbon steel and two new low-alloy, corrosion-resistant steels containing Cu-Sb and Cu was studied in a simulated seawater environment. The effects of Cu and Sb on corrosion resistance were analyzed by an electrochemical test and accelerated corrosion test. The results show that Cu and Sb reduce the corrosion current density by increasing the corrosion potential and increasing the polarization resistance. Sb can promote the formation of Cu-containing compounds with a strong corrosion inhibition performance, and it can enhance the overall corrosion resistance of steel. In addition, Sb can also promote the conversion of Fe2+ ions into a corrosion-resistant compound, α-FeOOH, and it also further improves the corrosion resistance of steel.

Investigation on the Impacts of Three Sea Salt Ions on the Performance of CSA-OPC Binary System

This study aimed to explore the impact of three corrosive ions—SO42−, Cl−, and Mg2+—on the hydration property of calcium sulphoaluminate (CSA) cement. Cement paste was prepared using three types of sea salt ion solutions with varying concentrations as mixing water. The experimental program encompassed assessments of porosity, compressive/flexural strength, heat of hydration, pH of pore solution, XRD, and SEM analysis. To modulate the hydration environment, Ordinary Portland cement (10%) was incorporated to elevate the pH and enhance the stability of ettringite, thereby facilitating the formation of additional C-S-H gel for the observation of M-S-H and other compounds. Findings revealed that the Cl− accelerated the hydration of CSA, resulting in heightened heat release. However, it also decreased the length-to-diameter ratio of ettringite, leading to cracking in CSA test blocks. The addition of SO42− resulted in elevated internal alkalinity, prompting alterations in hydration product types and subsequent reduction in CSA strength. Conversely, Mg2+ was observed to ameliorate the microstructure of CSA test blocks, diminishing porosity and augmenting strength.

Erosion depth prediction of chloride ions under stray current using FEM based CNNs

Stray currents can accelerate the transport of corrosive ions, especially Cl−, in concrete materials, which is very detrimental to structural safety. Effectively predicting the erosion depth of Cl− is crucial for evaluating structural safety. This article is based on a finite element model and verifies the erosion depth of Cl− under different voltages, Cl− concentrations, and corrosion time through experimental data. A polynomial was used to fit the quantitative relationship between erosion depth, Cl− concentrations, and corrosion time under single voltage condition. However, this formula only applies to a single voltage and has too many parameters. Therefore, this article also established a CNNs regression model to predict the depth of Cl−, and the results showed the multiple regression ability of CNNs. It has been proven that CNNs can accurately predict the erosion depth, which helps to accurately evaluate structural safety. After comparing experimental values, CNNs, ResNet, and ResNet-attention, it was found that residual networks and attention mechanisms did not significantly improve the prediction accuracy of deep networks, which may be related to insufficient data volume. After expanding the dataset, ResNet performed the best overall, and ResNet-attention had better testing performance, which is related to the powerful feature extraction ability of the attention mechanism.

Self-healing and corrosion-sensing multifunctional coatings containing pH-sensitive TiO2-based composites

Polyelectrolyte-encapsulated nanocontainers can effectively respond to changes of pH and thus control the on-demand release of corrosion inhibitors. A pH-responsive release system (Phen-Tpp@MTNs-PDDA) was developed based on the cationic polyelectrolyte poly dimethyl diallyl ammonium chloride (PDDA) encapsulated mesoporous TiO2 nanocontainers (MTNs) loaded with 1,10-phenanthroline (Phen) and tripolyphosphate ions (Tpp) corrosion inhibitors. The epoxy coating (EP) embedded with Phen-Tpp@MTNs-PDDA (Phen-Tpp@MTNs-PDDA/EP) demonstrates superior self-healing properties and confers long-term protection on the metal substrate through the cooperative effect of Phen and Tpp. Simultaneously, this hybrid coating is endowed with corrosion sensing capability based on the color development originating from the interaction of Phen and carbon steel. This self-healing and corrosion-sensing multifunctional coating provides an effective strategy for the corrosion protection of metals.

Research on the method of damage theory applied in underground lining structure’s durability

Damage or deterioration may occur in underground lining structures under the effects of external loads, groundwater seepage, and corrosive ions. Consequently, the durability and reliability of the structure can be severely affected. This study first analyzed and summarized the current situation of damage theory used in the durability research of concrete structures and underground. Consequently, the concept of a “deterioration degree function,” which can reflect the degree of damage to a structure, was proposed. Subsequently, the Gurson meso-damage model was analyzed for its application in the durability research of underground structures concerning the theory, formulae, and steps. A type of specimen was designed as an example, wherein the track model of steel corrosion expansion as assumed and deduced, and the numerical calculation of the damage stress was calculated to predict the durable life of the structure. The analysis concept developed in this study can be extended and applied to other research fields with similar durability problems.

A facile cleaner approach towards the synthesis of silver-doped cardanol-based hydrophobic antimicrobial and anticorrosive polymeric coating material

This work reports the solvent, catalyst and cross-linker free green synthesis of silver (Ag)-doped cardanol-based multifunctional polymer nanocomposite (PNC) coatings. The interaction of Ag ions with the polymeric backbone and in-situ formation of nanoparticles (NP) was confirmed by various characterization techniques. The optimum curing temperature (120–160 °C) and Ag concentration (1%) required for the free-standing film/coating with durable mechanical and chemical resistant properties in acidic/basic/salt solutions was studied. The high gel content (degree of crosslinking, 98%) and thermal stability up to 345 °C endorse the formulation of a well-cross-linked polymeric film/coating. XRD (approx. 27 nm) indicated the formation of crystalline silver nanoparticles within the polymer matrix, whereas SEM and TEM explored the distribution (200–700 nm). EIS studies for three weeks in 3.5% NaCl solution showed the exceptional corrosion inhibition efficiency (98-91%) of the coatings on steel substrate. The stable coating resistance value (MΩ.cm−2) throughout the study highlights the formation of a hydrophobic barrier with good resistance against the corrosive ions. Additionally, the potent antibacterial impact against Gram-positive, and Gram-negative bacteria, and the antifungal activity of the nanocomposite were attributed to the presence of Ag in the PNC. The multifunctional properties arise from the in-situ formed nanostructure and its synergistic effect with the biopolymer matrix projects its versatile industrial application.

Failure Analysis of Large-Size Drilling Tools in the Oil and Gas Industry

Abstract The safety problem of large-size drilling tools in large-size boreholes has become increasingly prominent with the exploration and development of deep and ultradeep wells. This study analyzes the causes of large-size drilling tool failures from the engineering point of view via statistical analysis, experimental material test, and vibration and bending analyses. Results show that the violent downhole vibration changes the drilling tool's mechanical properties. These changes result in an uneven distribution of hardness and reduced impact work, finally leading to the initiation of fatigue cracks at stress concentration points. Drilling tool bending is closely related to drilling parameters and bottom hole assembly (BHA) configuration. Unreasonable BHA configuration and drilling parameters increase BHA bending and accelerate fatigue failure. Once a crack is generated, the corrosive ions in water-based drilling fluids invade the microcrack, causing the corrosion of the drilling tool material. As a result, the strength is reduced, and the fracture is aggravated. Therefore, measures for preventing the failure of large-size drilling tools are proposed. We hope that the results of this work can provide useful guidance for drilling engineers.

Reinforcements/matrix micro-interface evolution and properties of in-situ Ni60A/WC coatings prepared by laser cladding

Ni60A/WC in-situ reinforced composite coatings are prepared on Inconel 718 alloy by laser cladding. The reinforcements/matrix micro-interface evolution, microhardness, and corrosion resistance are investigated. The phases in the coatings are mainly composed of γ-Ni, M23C6, M7C3 and NbC. The reinforcements/matrix micro-interfaces concerned in the coatings mainly include WC/matrix micro-interface and M23C6/matrix micro-interface. The WC/matrix micro-interface evolution is divided into five stages, namely, WC enters the molten pool, the micro-interface begins to grow, the reinforcements enriched at the tip, the reinforcements fall off and the formation of the stable micro-interface. The microhardness of the coatings increases with increasing WC content. On one hand, the increase in WC content promotes the generation of in-situ reinforcements, and the large lattice mismatch between dispersed reinforcement particles and matrix hinders dislocation motion. On the other hand, the two-dimensional mismatch degree of WC and γ-matrix calculated by Bramfitt's two-dimensional mismatch degree formula is 9.77 %, indicating that WC particles can serve as particles for γ heterogeneous nucleation. The increase of WC particles plays the role of fine grain strengthening, so the microhardness of the coating increases. The effect of WC on the corrosion resistance is also analyzed. The reinforcements are mainly distributed in the grain boundaries, and the HRTEM results indicate that a large degree of lattice mismatch exists in the micro-interface of reinforcements and γ-matrix. The large degree of mismatch shows that the interface between the two phases is relatively weak, and the weak interface is easy to become the channel for corrosive ion (Cl−) diffusion.

Anticorrosive effect of green sulfonated PANI-Zn with epoxy for the corrosion protection of aluminum alloy 6061-T651

The synergistic effect of epoxy resin and PANI-metal composites in anti-corrosion coatings is well known. However, the conventional chemical synthesis of PANI and its composites generates environmentally hazardous waste on an industrial scale. Given this, the study proposes synthesis of PANI-Zn composites by a “green” method to protect the AA6061-T651 alloy against corrosion. For the synthesis, hydrogen peroxide and sulphuric acid were used to promote polymerization and doping. PANI-Zn were characterized by FTIR, UV–Vis, XPS, XRF, ICP-OES and SEM. To prepare the coatings, 10 mg of composites were dissolved in 500 μL of ethanol/NMP solution (1:1) and mixed with 500 mg of epoxy resin and 250 mg of hardener. These were applied to AA6061-T651 alloys by the drop-casting method and allowed to stand at room temperature for 7 days, followed by heating at 70 °C for 1 h. After curing, the coatings were subjected to morphological (SEM and AFM), adhesion tests and electrochemical (EIS and linear polarization) characterizations. FTIR and UV–Vis spectra confirmed the structure of PANI in the materials. They also show that the composites are sulfonated and partially oxidized. XPS analysis demonstrated that the composites are in the protoemeraldine state (0 < y < 1; y ≠ 0.5) and that the presence of Zn in the synthesis influences the oxidation and doping state of the PANI. Furthermore, the XPS spectrum showed a weak ZnO signal only in PZn4, probably due to the amount of Zn used in the synthesis. However, XRF and ICP-OES confirmed the presence and content of zinc oxide in samples. Indeed, the anticorrosion performance of the composites varied according to their composition. The E-PZn2 (Epoxy-PANI-2 % Zn) was the best-performing coated electrode due to the morphology and distribution of the composites in the epoxy resin as well as good adhesion. This resulted in a better barrier effect against the penetration of corrosive ions, as well as providing anodic and cathodic protection by PANI, hydrogen sulfate ions, and ZnO.

Effect of chloride binding and sulfate ion attack on the chloride diffusion in calcium sulfoaluminate-based material under seawater environment

The diffusion of chloride ions in reinforced concrete under the seawater environment will affect the physical or mechanical properties and durability. Sulfate ions also influence the diffusion of chloride ions by generating expansion products through physical and chemical reactions. Further research on the effects of chloride binding and sulfate ion attack on chloride ion diffusion will deepen the understanding of concrete failure mechanism. In this paper, a quaternary blend based on calcium sulfoaluminate (CSA) cement was prepared and laboratory immersion tests were conducted in artificial seawater with varying salt concentrations. Initially, chloride ion concentration measurements and XRD tests were conducted at different corrosion ages and salt concentrations. Subsequently, the chloride binding properties of CSA-based materials was quantified through the analysis of chloride ion concentration and the phases of hydration products. Meanwhile, the corrosive effect of sulfate ions on chloride ion diffusion was determined corresponds to the content of expansive hydration products. Furthermore, numerical simulations were employed to evaluate the impact of sulfate ion corrosion, chloride binding, and their combined effects on chloride ion diffusion, and the results were compared with free chloride ion concentration (Cf). The results indicate that the total chloride ion concentration (Ct) exhibits a linear relationship with increasing salt concentrations of seawater in CSA-based materials. Meanwhile, the bound chloride ion concentration (Cb) follows a logarithmic growth pattern. The chloride binding rate experiences a linear decline with the increase of chloride ion concentration in the artificial seawater. Additionally, the relationship between Cf and Cb or Ct can be described using different isothermal adsorption models for the CSA-based materials. Among these models, the Langmuir model is suitable for characterizing the relationship between Cf and Cb, while the Freundlich model is suitable for describing the relationship between Cf and Ct. Furthermore, it is noteworthy that sulfate ion attack and chloride binding exert nearly equivalent effects on the diffusion of chloride ions in CSA-based materials at short corrosion age and low chloride ion concentration. However, the corrosive impact of sulfate ions gradually evolves into the dominant factor in the progression of corrosion over time and the increase in seawater salt concentration.

The Role of Rare Earths on Steel and Rare Earth Steel Corrosion Mechanism of Research Progress

Corrosion has always been an important factor affecting the life of steel, which causes huge economic losses every year. How to improve the corrosion resistance of steel has always been a research focus. Adding rare earth elements into steel is an important method to improve the corrosion resistance of steel. In this paper, the effects of rare earth elements on steel are summarized, including the purification of molten steel, modification and modification of inclusions, improvement of grain boundaries by solid solution strengthening, the influence of phase transformation and the refinement of microstructure, and reduction in C and N desolubilization. On this basis, the progress of research on the corrosion resistance mechanisms of rare earth steel is summarized, focusing on rare earth-modified inclusions. This includes the changes in composition and sizes of inclusions by rare earth addition, promoting the transformation of MnS and Al2O3 in rare earth inclusions with regular shapes, smaller sizes and better performance, or composite rare earth inclusions. The corrosion pits that form in the early stages of corrosion are shallow in depth, fewer in number and light in corrosion degree. The effects of rare earth materials on the rust layer include: rare earth promotes the formation of a more stable corrosion product α-FeOOH, and rare earth promotes the formation of a dense rust layer, which covers the surface of the matrix and hinders the transmission of corrosion ions. The protective effect of the rare earth atomic layer on the substrate and the corrosion inhibition effect of rare earth ions are formed by the segregation of rare earth at the interface. In the end, the existing problems in the research into rare earth steel and future research directions are briefly put forward, including improving the addition process of rare earth steel, theoretical guidance on enhancing the corrosion resistance mechanism of rare earth steel, and extending the research from La, Ce, and Y steel to more rare earth steels.

Microstructure and Chlorine Ion Corrosion Performance in Bronze Earring Relics.

Chlorine ions play an important role in the corrosion of bronzeware. This study employs techniques such as XRD, OM, SEM, EBSD, and electrochemical testing to analyze the microstructure, crystal structure, chemical composition, and corrosion performance of bronze earrings unearthed at the Xindianzi site in Inner Mongolia. The results indicate the presence of work-hardened structures, including twinning and equiaxed crystals, on the earrings' surface. With an increase in chloride ion concentration in NaCl solutions from 10-3 mol/L to 1 mol/L, the corrosion current density of the bronze earrings increased from 2.372 × 10-7 A/cm2 to 9.051 × 10-7 A/cm2, demonstrating that the alloy's corrosion rate escalates with chloride ion concentration. A 3-day immersion test in 0.5% NaCl solution showed the formation of a passivation layer of metal oxides on the earrings' surface. These findings underscore the significance of the impact chloride ions have on the corrosion of copper alloys, suggesting that activating the alloy's reactive responses can accelerate the corrosion process and provide essential insights into the corrosion mechanisms of bronze artifacts in chloride-containing environments.

Effect of voltage on microstructure and corrosion resistance of micro-arc oxidation coating on Mg–Zn–Ca biodegradable alloy

This work discussed the influences of voltage on the microstructure and corrosion resistance of micro-arc oxidation (MAO) coating developed on Mg–2Zn-0.3Ca (ZX20) alloys. The MAO coatings on ZX20 alloy surface consist of MgO and Mg2SiO4 compounds. They feature two layers, namely a porous outer layer and a dense inner layer. Higher voltage forms a thicker MAO coating on ZX20 alloy, meanwhile, larger diameter micropores and more thermal micro-cracks are generated in the coating. The MAO coating on ZX20 alloy obtained at 400V has the largest thickness (5.98 ± 0.23 μm), the largest diameter of the micropores (1.02 ± 0.64 μm), the most thermal cracks and the most amount of Mg2SiO4. The MAO coating on ZX20 alloy obtained at 300V has the largest contact angle value and the highest bonding strength. During the immersion corrosion, the corrosive ions such as Cl− can enter the outer layer of the coating and react with MgO to generate Mg(OH)2, resulting in the dissolution of the coating. With the prolong of the immersion time, local corrosion and cracks form at the weak site of the coating, speeding up the corrosion. While, the dense inner layer containing chemically stable Mg2SiO4 has less defect, providing an effective physical barrier for the substrate and enhancing the corrosion resistance of ZX20 alloy. The ZX20 alloy coated at 300V exhibits the lowest degradation rate (PH = 0.13 mm y−1) due to its dense inner layer, as well as having the largest contact angle value and the highest bonding strength.

Corrosion resistance and ion exchange properties of montmorillonite film on AZ31 in SBF solution

Montmorillonite (MMT) film was prepared on the surface of alkali-heat treated Mg alloys by one-step hydrothermal method. The structure and composition of MMT film were characterized using scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The corrosion resistance of MMT film in simulated body fluid (SBF) was investigated using electrochemical tests and immersion experiments. The experimental results showed that with the extension of hydrothermal time, the corrosion resistance of film increased and then decreased. With the increase of MMT powder mass fraction in precursor solution, the corrosion resistance of films also increased and then weakened. The best performance of MMT films was obtained at hydrothermal time of 12 h and MMT powder mass fraction of 2 wt%, with an impedance value of 9.77×106 Ω·cm2, which is an improvement of four orders of magnitude compared to substrate, and the efficiency of corrosion protection was up to 100%. The ion exchange properties, barrier effect and inertness characteristics of MMT provide excellent corrosion protection for magnesium substrates. This study provides a new coating strategy for the preparation of biodegradable magnesium alloys with excellent corrosion resistance and biocompatibility for use as biomedical materials.

A silicon photoanode protected with TiO2/stainless steel bilayer stack for solar seawater splitting

Photoelectrochemical seawater splitting is a promising route for direct utilization of solar energy and abundant seawater resources for H2 production. However, the complex salinity composition in seawater results in intractable challenges for photoelectrodes. This paper describes the fabrication of a bilayer stack consisting of stainless steel and TiO2 as a cocatalyst and protective layer for Si photoanode. The chromium-incorporated NiFe (oxy)hydroxide converted from stainless steel film serves as a protective cocatalyst for efficient oxygen evolution and retarding the adsorption of corrosive ions from seawater, while the TiO2 is capable of avoiding the plasma damage of the surface layer of Si photoanode during the sputtering of stainless steel catalysts. By implementing this approach, the TiO2 layer effectively shields the vulnerable semiconductor photoelectrode from the harsh plasma sputtering conditions in stainless steel coating, preventing surface damages. Finally, the Si photoanode with the bilayer stack inhibits the adsorption of chloride and realizes 167 h stability in chloride-containing alkaline electrolytes. Furthermore, this photoanode also demonstrates stable performance under alkaline natural seawater for over 50 h with an applied bias photon-to-current efficiency of 2.62%.

Constructing PANI@CF hybrids enhanced epoxy coatings with integrated functionalities of interfacial enhancement, erosion wear resistance and anti-corrosion

Factors such as sediment erosion and diffusion of corrosive ions in the splash zone result in a serious decrease in the protective performance of organic coatings. Carbon fiber (CF) reinforced polymer coatings have attracted much attention due to the impressive high mechanical strength and reliable chemical stability, but their protection period for steel structures is usually limited by the surface inertness and poor interfacial compatibility of the original CF. Herein, we created a composite coating with excellent erosion and wear resistance and corrosion resistance through simple self-polymerization of polyaniline on carbon fibers. The PANI layer not only helped to improve the interfacial compatibility between fibers/resin, but also exerted its corrosion inhibition effect. The interfacial shear strength (IFSS) value of the modified PANI4@CF monofilament and resin (60.63 MPa) was 46.73 % larger than that of the unmodified CF monofilament. In the simulated splash zone, PANI4@CF5/EP composite coating showed the best erosion resistance and corrosion resistance, and the mass loss and volume loss after erosion test were reduced by 53.39 % and 50.10 %, respectively, compared with pure epoxy coating. The local electrochemical impedance spectroscopy (LEIS) value of PANI4@CF5/EP coating with artificial defect was one order of magnitude higher than the epoxy coating after 48 h immersion. Finally, the environmental conditions of the splash zone were simulated to evaluate the anti-corrosion performance and erosion resistance of the CF reinforced composite coatings, and the protective mechanism was discussed in depth, which has great significance to the development of protective coatings for the splash zone under extreme marine environments.

Sonication assisted superior anti-corrosion properties of cathodically deposited novel nickel-graphene oxide-zinc oxide coating

This study details the sonication-assisted synthesis and characterization of a cathodically deposited novel nickel-graphene oxide -zinc oxide (Ni-GO-ZnO) composite coating achieved through electrodeposition and its comparison with anodically deposited GO. This coating was comprehensively characterized using Fourier-transform infrared (FTIR), X-ray diffraction (XRD), Raman spectroscopy, Field emission scanning electron microscopy (FE-SEM) coupled with Energy-dispersive X-ray spectroscopy (EDAX). Subsequently, its corrosion resistance for MS1010 mild steel in 3.5 wt % (NaCl) was evaluated via weight loss, contact angle, electrochemical impedance spectroscopy (EIS), Potentiodynamic polarization, and surface analysis techniques. These observations suggest that graphene oxide-zinc oxide (GO-ZnO) adsorbs nickel onto the MS surface effectively and reduces defects, which helps in blocking active corrosion sites. Tafel plots and EIS revealed that the Ni-GO-ZnO coating exhibited the lowest current density (39.95 µAcm²) and the highest charge transfer resistance (1211 Ωcm²). This was further validated by long-term immersion testing, where the Ni-GO-ZnO coating exhibited significantly less weight loss (1.33 mils/Y) compared to the deposited GO coating (2.2 mils/Y). The mechanism of formation of deposited GO and Ni-GO-ZnO coating on the metallic surface is proposed. The enhanced corrosion resistance of the Ni-GO-ZnO coating is attributed to its ability to 1) form a more compact metallic layer and 2) Minimize the active surface area vulnerable to corrosion attack. 3) Diminishes the presence of holes and cracks for corrosive ion ingress.4) Functionally impedes the ingress of chloride ions, primarily liable for steel degradation. The synergistic effect of the GO-ZnO constituents within the nickel matrix significantly enhances the long-term durability and integrity of the protective layer, a phenomenon hitherto unexplored. The empirical outcomes advocate for the advanced application of GO-ZnO-nickel coatings in safeguarding infrastructural materials against corrosive degradation.

Particle Properties of Air Nanobubbles and Their Inhibition Mechanism on Brass Corrosion in Recirculating Cooling Water: Effects of Concentration Ratio and Flow Velocity

AbstractThe corrosion inhibition performance of air nanobubbles (A‐NBs) is expected to address the environmental problems arising from chemical corrosion. In order to regulate the corrosion inhibition performance of A‐NBs, the particle characteristics of A‐NBs in flowing composite salt solutions are investigated, and the corrosion inhibition effect of A‐NBs under different concentration ratios and rotational speed of simulated circulating cooling water is studied. High salt concentrations significantly reduced the particle size, concentration, and zeta‐potential value of A‐NBs, thus reducing the stability of A‐NBs. The flow velocity has a slight effect on A‐NBs. The results of the weight loss and electrochemical method showed that A‐NBs achieved the highest corrosion inhibition rate of 55% under a concentration ratio of 1.5 and a rotational speed of 100 r min−1. The surface characterization of brass specimens revealed that A‐NBs facilitated the formation of Cu2(OH)2CO3 passivation film, calcium carbonate scale film, and a layer of bubbles on the surface of brass, which subsequently mitigated the erosive impact of the fluid. A‐NBs can adsorb cations and thus reduce the concentration of corrosive ions. However, the increase in concentration ratio and rotational speed impeded the formation of the bubble layer and passivation film.

Sulfate resistance of carbonated basic oxygen furnace slag-metakaolin-Portland cement blends

Basic oxygen furnace slag (SS) is prone to carbonation due to its alkaline properties. The combined use of carbonated basic oxygen furnace slag (CSS) with metakaolin (MK) as a composite supplementary cementitious material (CSS-MK) can improve the reactivity of CSS and significantly lower the overall embodied CO2 emission. However, the impact of CSS-MK on the resistance of external sulfate attack (ESA) of cement remains unclear. This study aims to clarify the influence of CSS-MK on the resistance of cement to ESA. Compressive strength, water absorption, and electrical flux before ESA, and macro-scale expansion, microstructure, and evolution of phase assemblage during ESA were investigated. Results indicate that CSS-MK exhibits higher strength reactivity compared to SS-MK, enabling a 30% cement replacement level without compromising compressive strength after 7 days. CSS-MK reduces water absorption by 37.9% and electrical flux by 67.6%, enhancing transport property and reducing sulfate ion intrusion into the cement paste. The carbonation treatment transforms calcium silicate in SS into CaCO3, decreasing soluble calcium content, and creating a CaCO3-based passivation layer that inhibits sulfate ion corrosion. Meanwhile, the reaction in CSS-MK blends between the CaCO3 in CSS and MK consumes Ca(OH)2, forms ettringite and thermodynamically more stable carboaluminate, and results in the absence of monosulfate prior to ESA and the presence of carboaluminate during ESA, which consequently decreases ettringite content by 40% in paste after 240 days of ESA. Furthermore, at the macroscopic level, the expansion decreased by 85.2% after 360 days of ESA, effectively mitigating specimen cracking and damage.