Journal of Functional Analysis

Wang T., Zhang H., Wang R., Wu C., Zhang S., Zhang C., Liang X.

Five Fe-based composite coatings with different weight ratios of Nb were prepared by laser cladding on 0Cr13Ni5Mo substrate. As the Nb content imposes, the NbC content gradually increases; the microstructure was refined; and the NbC morphology changed from quadrangle carbides to petaloid and papilionaceous carbides. Meanwhile, the microhardness and wear resistance of the composite coating gradually improve. The S3 coating exhibited a high microhardness of approximately 610 ± 12.2 HV and an excellent wear resistance. The S3 coating showed the highest corrosion resistance in 3.5 wt-% NaCl solution with Ecorr and Icorr of −179.3 mV and 9.258 × 10−8 A/cm2, respectively. The improvement in the corrosion resistance could be attributed to the fact that the forming NbC would consume amounts of C in the matrix; thus, the Cr atoms were released from its carbide state, and then dissolved in the matrix.

Chen X., Xie Y., Wu Y., Bian J., Ma C.

The corrosivity of molten salt can be detrimental to the safe operation and longevity of concentrated solar thermal power generation equipment. Additionally, the presence of impurity Cl− can increase corrosion on metal materials, leading to mechanical property degradation. To assess the extent of this effect, the corrosion behaviour of three types of stainless steel (304, 316L, and 347H) in molten salt at high temperatures was studied using the loss-in-weight method and tensile tests. According to the findings, the Rdepths of 304, 316L, and 347H stainless steels are 0.0018 mm/a, 0.0016 mm/a, and 0.0019 mm/a, respectively, resulting in a decrease in elongation of 12.2%, 7.0%, and 3.7% after 720 h of corrosion at 600°C. Furthermore, at a higher temperature of 680°C, the Rdepths of all stainless steels increased, and the elongation decreased by 25.4%, 18.9%, and 13.5%, respectively. Similar corrosion behaviour was observed in 347H stainless steel with increased chloride ion concentration. However, the yield strength and tensile strength of stainless steel did not exhibit significant changes under different experimental conditions. The corrosion mechanism of metal alloys in molten salt is mainly due to the selective corrosion of Cr and its dissolution into molten salt in the form of ions.

Fan J., Dong L., Zheng H., Wang Q., Li L., He Y.

The influence of Ti content on the microstructure and corrosion behavior of nickel-based alloy 825 in acid oil and gas environments was studied. The pitting corrosion behavior and stress corrosion cracking (SCC) behavior of Alloy 825 were investigated using high-temperature and high-pressure immersion tests, electrochemical tests, and slow strain rate tensile tests. Scanning electron microscopy, electron backscatter diffraction, and 3D microscopy were applied to analyze the microstructure and corrosion performance of the samples. The results showed that the number of inclusions and residual strain increased with the increase of Ti content, and strain concentration was found around the inclusions. The rise in inclusions led to lower pitting potential and a narrower passivation interval. In addition, the enhanced SCC susceptibility of the alloy with higher Ti content may also be attributed to the increase in inclusions.

Tiwari A.K., Dogra P., Goyal S., Luxami V.

This paper explores the influence of 2-aminopyridine (2AP) as water-based migratory corrosion inhibitor (M-CoI) on the corrosion resistance of reinforcing steel bars embedded in ordinary Portland cement and pozzolanic Portland cement concrete subjected to combined chloride and carbonation ingress. Two applications of 2AP are considered i.e., preventive (applied before exposure to aggressive environment) and repair (applied after corrosion initiates). Corrosion performance was assessed using electrochemical techniques and gravimetric mass loss method. The study also examines the impact of 2AP application on chloride ion concentration and carbonation depth of both concrete systems. The compressive strength of each concrete system was also measured to study the impact of M-CoI application on strength properties. Surface condition of hardened concrete and extracted rebar was evaluated by optical microscopy. Results conclude that 2AP effectively retards reinforcement corrosion when used as preventive measure by forming a homogeneous inhibitive layer on steel. However, when used as a repair technique, localised and uniform corrosion was perceived. An attempt has been made to identify the cause of non-performance of 2AP as repair measure. It was concluded that reached concentration of 1 mM was not sufficient to reduce ongoing corrosion due to the accumulation of corrosion products. The influence of the inhibitor on chloride profile and carbonation depth was found to be insignificant. It is concluded that chloride ions initiate the corrosion mechanism, while carbonation exacerbates it, particularly in blended cement concrete. Nonetheless, inhibitor application can provide similar resistance in both concrete systems.

Wang Q., Zhao X., Qu Y., Zhong B., Tan H., Zheng Y., Yang X., Shichao G., Hu J., Yuan H.

In recent years, graphene has remarkably enhanced the protective performance of anticorrosive organic coatings, yielding increasingly frequent exciting results and perspectives. This paper reviews the latest research advancements that we have gathered on the influences of conductivity, modification, dispersion methods and controllable orientation of graphene; the graphene-based smart anticorrosive coatings; the current understandings on the designs of the anticorrosive coating and the action mechanisms of graphene in the coating. It is concluded that there would be greater opportunities for the gravitational field-induced method to play the shielding effect of graphene; noncovalent modification methods may not ensure satisfactory attachment of the modifiers to the surface; green modification methods are expected to reduce the electrical conductivity of graphene and covalently modify graphene; the self-healing and early-warning graphene-based anticorrosive coatings are becoming a trend in the development of anti-corrosive coatings. The current-faced challenges and the future development prospects of the graphene-based anticorrosive coating were also proposed. Although graphene performs well in anticorrosive coatings, there is still considerable room to improve the performance, and a new round of industrial optimisation and upgrading in the anti-corrosion coating industry is inevitable with the rapid development of the anticorrosive graphene-based filler.

Upadhyay N., Shankar A.R., Ningshen S.

The present investigation involved the execution of electrochemical corrosion tests on three distinct modified 9Cr–1Mo steel alloys, each characterised by varying nitrogen and boron contents. These alloys, denoted as P91 (B=0, N=330 ppm), P91B (B=100 and N=20 ppm) and P91BN (B=60 and N=110 ppm), underwent exposure to varying concentrations of NaOH (0.1, 0.2 and 0.5 M) solutions. Additionally, the study explored the influence of chloride (0.1 M NaCl) on the occurrence of pitting corrosion within an alkali environment. The results indicated that the passive current density in all the concentrations of NaOH studied is maximum for alloy P91 followed by P91B and P91BN, respectively, indicating alloy P91 is more prone to corrosion than alloy P91B and P91BN. Electrochemical impedance spectroscopy demonstrated a higher polarisation resistance value for P91BN and the lowest for P91. Scanning electron microscopy analysis revealed that in alloy P91B and P91BN, pits are formed at the M23C6 carbide/matrix interface whereas in alloy P91 apart from carbides, pits are formed at inclusions. Energy-dispersive X-ray mapping identified the elemental composition of the inclusion in P91 which is found to be complex Al2O3–MnS inclusions enriched with Mo. P91BN demonstrated better pitting corrosion resistance compared to alloys P91 and P91B when exposed to NaOH+NaCl medium.

Zhang J., Qin S., Wang F., Li R., Shi Y., Xu Y.

Fe2O3/Fe3O4 composite films were successfully prepared on the surface of X80 steel through hydrothermal synthesis and annealing treatments. Subsequently, the oxidised films were modified using surfactants such as decanoic acid (DA), decyl silane triol (DS) and perfluorodecyl silane triol (FDS), resulting in the creation of three distinct films exhibiting superhydrophobic properties. The effects of the hydrophilic and hydrophobic groups of surfactants on the superhydrophobic films of X80 steel were analysed using electrochemical methods, surface analysis techniques and theoretical calculations. The results showed that all three superhydrophobic films exhibited excellent corrosion resistance, with the order being DA > FDS > DS after 72 h of immersion in acidic conditions (pH = 6, 60 °C). Theoretical calculations showed that the adsorption performance of carboxyl groups was superior to that of silyl alcohol bonds, whereas fluorination of hydrophobic groups helped to enhance the adsorption capacity of hydrophilic groups. This not only reveals the key role of surfactants in the preparation of superhydrophobic membranes but also provides a theoretical basis for the preparation of superhydrophobic membranes on carbon steel surfaces.

Ramlan D.G., Norizan N.A., Zulfaisal N.A., Othman N.K., Yaakob N.

Wet gas pipelines transport unprocessed natural gas that contains water and carbon dioxide (CO2), which combination can lead to severe wall loss caused by CO2 or sweet corrosion in carbon steel. Under specific conditions, CO2 corrosion occurs at the top section of the pipeline, which is known as top-of-the-line corrosion (TLC). TLC tests were conducted in the water-hydrocarbon co-condensation environment using 10 vol% n-heptane and 25 vol% n-heptane to simulate the internal condition of a wet gas pipeline to study the effect of hydrocarbon volume ratio towards TLC. The presence of n-heptane showed minimal effect on the gas temperature profile; however, n-heptane suppressed the water condensation, resulting in a tremendous decrease in the water condensation rate (WCR). The TLC rates were found to be lower in the presence of n-heptane, which can be attributed to the reduced WCR and water-wetted areas. The presence of n-heptane had no significant effect on the pitting rates but showed an increasing pit ratio as the n-heptane volume increased. TLC tests were conducted at three durations: one day, two days and three days showing that n-heptane has no significant effect on corrosion kinetics.

Lu H., Li S., Wang Y.

Molten NaCl–KCl–MgCl2 is becoming a potential heat transfer fluid (HTF) and thermal energy storage (TES) material in the third generation of concentrated solar energy power (CSP) stations due to its excellent heat storage-capacity and thermal stability. However, the strong corrosion of the molten chloride salt at high temperature limits its industrial application. In this study, the corrosion behaviour of FeCoNiCrAl HEA with BCC + FCC phase structure in molten NaCl–KCl–MgCl2 (24.5–20.55–54.95 wt-%) at 650 °C under argon was investigated by a combination of weight loss and electrochemical methods. The results show that, the corrosion of FeCoNiCrAl HEA in molten chloride salt mainly manifests as the selective dissolution of Fe and Cr. With the further increase of immersion time, oxides gradually crack and slightly flake, resulting in large weight loss of FeCoNiCrAl HEA.

Momber A.W., Marquardt T., Irmer M., Kelm D.

Damages to multilayer organic coating systems due to impact loads can deteriorate the corrosion protection performance of the coatings under offshore exposure. The contribution is concerned with statistical investigations into the effects of load-based and coating-based factors on the protection performance of impinged coating systems for offshore wind power structures. Accelerated cyclic laboratory tests were performed on damaged multilayer coating systems, and the results were statistically analysed. Results of analysis of variance revealed that the effects on the integral corrosion protection performance of the coatings (anticorrosive effect, AE) were dominated by the factor ‘load intensity’ (impact energy). This factor could explain 34% of all effects. It also was the only significant factor. The load-based factor ‘damage area’ affected the coating delamination and was extremely significant, but it did not affect the AE. Coating-based factors, namely ‘coating system’, ‘total dry film thickness’ and ‘pull-off strength’, did not deliver effects to AE and were statistically insignificant. The factor ‘coating system’ was statistically insignificant for delamination and for AE. ‘Unknown’ effects, not considered in this study, delivered the highest contributions to the regression models (50% to 68%), indicating that additional parameters/factors of the coating systems must be considered when developing impact-resistant coatings.

Lei B., Li J., Liu L., Lian L., Chen S., Zhang S., Feng Z., Meng G.

In this study, Ce3+ functionalised halloysite nanotubes (HNTs) were prepared, and their impact on the anticorrosion properties of waterborne polyurethane (WPU) coating on 7075 aluminium alloy (AA7075) was investigated. HNTs were grafted by 3-aminopropyltriethoxysilane (APTES) to enhance Ce3+ loading, which was confirmed by X-ray diffraction (XRD) and Fourier-transform infrared (FT-IR) spectrum. The release behaviour of Ce3+ from HNTs was tested by inductively coupled plasma optical emission spectrometry (ICP-OES), and the inhibition effect of Ce3+-loaded HNTs for AA7075 was tested by polarization plots. The anticorrosion property of WPU doped with Ce3+-loaded HNTs was investigated by electrochemical impedance spectroscopy (EIS) and pull-off adhesion test. The results showed that APTES modification improved the Ce3+ loading amount on HNTs, and Ce3+ acts as an effective cathodic inhibitor for AA7075. After soaking for 40 days, the |Z|0.01Hz of Ce-HNTs/WPU was two orders of magnitude higher than that of pure WPU, while wet put-off adhesion was higher than pure WPU.

Zhang S., Du X., Shi W., Xiang S.

The tribocorrosion of titanium implants is the primary cause of their late failure. As the most promising third-generation medical β-type titanium alloy, Ti-13Nb-13Zr (TC26) demonstrates superior corrosion resistance and harmless chemical element composition, making it an excellent alternative to Ti-6Al-4V alloy (TC4). Nonetheless, this study has revealed a significant weakness of TC26 in tribocorrosion properties under low dissolved oxygen concentration conditions, which could pose potential hazards in subsequent medical applications. The effects of low dissolved oxygen concentration on the tribocorrosion properties and ion release were examined using electrochemical methods, laser confocal microscopy, scanning electron microscopy, and inductively coupled plasma emission spectrometer. The findings indicate that TC26 exhibits significantly inferior corrosion resistance compared to TC4 due to the sluggish recovery rate of the passivation film under low dissolved oxygen concentration conditions during wear. Moreover, TC26 experiences greater mechanical wear loss than that of TC4. However, under the synergistic effect of wear and corrosion, TC26 releases a minimal amount of ions, while excessive harmful Al ions are released by TC4.

Khoma M., Vynar V., Chuchman M., Vasyliv C., Ivashkiv V., Halaichak S.

The effect of hydrogen sulphide concentration on the corrosion behaviour of 07Cr16Ni6 austenitic-martensitic stainless steel in a 5% NaCl  +  0.5% CH3COOH solution was studied to determine the role of H2S in the corrosion product formation and corrosion mechanism. Unstable passivation of steel is detected in a solution containing <100 mg/dm3 H2S. Steel corrodes in an electrochemically active state at >100 mg/dm3 H2S. When the pitting potential is reached, pitting damage occurs at the grain boundaries. The corrosion rate decreases by ∼five times after exposition for 720 h due to the formation of nickel and iron sulphides on the surface. Corrosion is accompanied by the absorption of 4.2–17.5 ppm hydrogen, 62…70% of which is diffusible and can cause hydrogen embrittlement. The scheme of steel corrosion under the influence of different concentrations of hydrogen sulphide is proposed.

Hao K., Xia W., Li Q., Yan H., Chen J., Su B.

Microalloying is an effective method to improve the properties of Al–Mg alloys. The microstructure, mechanical properties and corrosion behaviours of Al–9.2Mg–0.8Mn– xCu ( x = 0–1.2 wt-%) alloys are studied to promote the application of Al–Mg alloys. The addition of Cu increases the strength of the alloy, where the ultimate tensile strength of 0.6 wt-% Cu alloy is improved by 43 MPa. Moreover, the addition of Cu significantly affects the corrosion behaviours of alloys. For as-sensitised alloys, compared to the matrix, the 0.1 wt-% Cu alloy shows a 28.3% reduction in pitting corrosion mass loss, which is attributed to the Cu element can form a stable passivation film, and the 0.3 wt-% Cu alloy shows a 15% reduction in intergranular corrosion mass loss, which is attributed to the addition of Cu can restrict the β phase precipitation at grain boundaries. The study shows that Cu-alloying can improve the comprehensive properties of Al–9.2Mg–0.8Mn alloys.

Tamimi M.F., Alshannaq A.A., AbuQamar M.I.

The randomness of atmospheric conditions is among the key contributing factors that affect the ability to accurately predict the corrosion growth in steel structures. Climate change has the potential to alter the long-term characteristics of these factors over the lifespan of steel structures, both those already existing and those newly built. The impact of climate variability on the stochastic nature of atmospheric variables, which greatly influence corrosion conditions, can add complexity to corrosion predictions in these structures. This paper introduces an integrated framework to quantify the impact of climate change on corrosion rates of steel structures worldwide. It considers the changes in environmental conditions, specifically temperature, relative humidity and wind speed and their effects on atmospheric corrosion. Global Climate Models are employed to evaluate the long-term impacts of climate change on these environmental conditions. An analytical model for predicting corrosion rate is integrated with climate change models to predict alterations in the corrosion rates of steel components relative to historical conditions. This paper also discusses the impact of climate change on the variations of these climatic parameters and offers a comparison between historical data and projected conditions across the globe. The results indicate that the effect of climate change on the corrosion rate depends on the considered region. While regions such as Australia, North America and Europe see an increase, others such as Asia and Africa observe a decline. Notably, all oceans, especially the Antarctic and Arctic, experience a significant increase in corrosion by the end of the century.