Galvanic corrosion of Ni–Cu–Al composite coating and its anti-fouling property for metal pipeline in simulated geothermal water

A novel anti-fouling epoxy-silicone composite coating containing Ni–Cu–Al alloy powder for metal pipeline in geothermal water was fabricated based on the basic principles of galvanic corrosion. Fouling behaviors of the surface of composite coating in the simulated geothermal water were studied in comparison with stainless steel and epoxy-silicone resin coating. The results indicated that composite coating possessed a good anti-fouling performance. In the geothermal water, Ni²⁺, Cu²⁺ and Al³⁺ ions, originated from interface electrochemical corrosion, were released into bulk solution. These metal ions intensively inhibited nucleation and crystal growth rate of CaCO₃ fouling on the surface of composite coating, and promoted precipitation of CaCO₃ fouling in the bulk-solution, which could be easily washed away by flowing water. But for 304 stainless-steel and epoxy-silicone resin coating, CaCO₃ fouling grew easily and adhered firmly to their surfaces, and influenced the transport efficiency of geothermal water for pipelines.     

Improvement of the corrosion characteristics of 1.4713 ferritic steel in 0.1 M sulfuric acid by heat treatment and Al2O3–TiO2 coating

This study addresses the influence of heat treatment and alumina coating on the corrosion of EN 1.4713 steel in 0.1 mol dm⁻³ sulfuric acid. The corrosion characteristics of three different samples are examined using the open circuit potential measurements, Tafel extrapolation, linear polarization resistance, weight-loss method, and electrochemical impedance spectroscopy. The results showed that the application of the weight-loss method yielded similar values to the electrochemical method in the first 24 h. A decrease in corrosion rate, in a similar manner, was observed for all three samples. The largest deacceleration was obtained for the alumina/titania-coated sample. It was obtained that the heat treatment significantly increased the corrosion resistance, but only in the first 24 h. The alumina/titania coating decreases the corrosion rate by approximately 30 times at the beginning of the corrosion exposure and by nearly 300 times after 240 h. This coating could have a significant influence on construction design, which uses ferritic stainless steel as the material.     

Effects of NH4+, Na+, and Mg2+ ions on the corrosion behavior of galvanized steel in wet–dry cyclic conditions

The effect of cations on the corrosion of galvanized steel (GS) is scarcely reported. In this study, a wet–dry cyclic test was conducted to study NH₄ ⁺, Na⁺, and Mg²⁺ cation effect on the corrosion behavior of GS available in Nepal. Fourteen wet–dry cycles (18 h wet and 6 h dry) were performed by exposing samples at 298 K with a relative humidity of 90% in a wet cycle and 50% in a dry cycle for 14 days. The cations strongly affect the corrosion rate of the GS sample estimated by weight loss and potentiodynamic polarization. The potentiodynamic polarization curves showed the inhibition of cathodic and anodic reactions by Mg²⁺ ion, while the NH₄ ⁺ ion only changed the cathodic reaction. Mg²⁺ ion was found to shift the corrosion potential to noble values compared with NH₄ ⁺ and Na⁺ ions. A compact and thin corrosion products layer was developed in Mg²⁺ salt solution in contrast to a thick and porous corrosion products layer in NH₄ ⁺ and Na⁺ salt solutions. Red rust due to corrosion of underlying steel appeared in the presence of NH₄ ⁺ and Na⁺ salt solutions. Finally, the weight loss data revealed that the corrosivity of cations for GS decreased in the order Na⁺ > NH₄ ⁺ > Mg²⁺.     

Effect of Y2O3 content in the pack on microstructure and hot corrosion resistance of Y–Co-modified aluminide coating

Y–Co-modified aluminide coatings on nickel base superalloys were prepared by pack cementation method. Effect of Y₂O₃ content in the pack mixture on microstructure and hot corrosion resistance of the coatings was investigated. The results show that with the increase in Y₂O₃ content, the content of Co in the coatings increases. The mass gain of the coatings with Y₂O₃ addition of 1, 2 and 3 wt.% is 0.6, 0.55 and 0.42 mg/cm² after hot corrosion at 1173 K for 100 h, respectively. Y₂O₃ addition accelerates the diffusion of Co and thus increases the hot corrosion resistance of the coating.     

Insights into the cut edge corrosion of 55% Al–Zn metal coating on steel from simultaneous electrochemical polarization and localised pH sensing experiments

Band microelectrode arrays were used to model the cut edge corrosion behaviour of 55% Al–Zn (Galvalume/Zincalume) and Zn coated steels in chloride and sulfate electrolytes. Simultaneous electrochemical polarization experiments revealed increased cathodic current on the steel during anodic dissolution of neighbouring Al–Zn alloy electrodes. The increased cathodic current on the steel was shown to be a result of pH buffering by Al³⁺, enhancing the rate of hydrogen evolution. A large negative shift of the corrosion potential of the Al–Zn alloy electrodes was observed during cathodic polarization on neighbouring steel electrodes and was attributed to alkaline pH generated from cathodic processes.     

Preconditioning of AISI 304 stainless steel surfaces in the presence of flavins—Part I: Effect on surface chemistry and corrosion behavior

Stainless steel AISI 304 surfaces were studied after a mild anodic polarization for oxide growth in the presence and absence of two derivatives of vitamin B2 (riboflavin and flavin mononucleotide) that can be secreted by metal-reducing bacteria and act as a chelating agent for iron species. The alterations in oxide chemistry were studied by means of surface-sensitive techniques such as X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry analysis. The complementary electrochemical characterization revealed a preferential growth of an oxide/hydroxide iron-rich film that is responsible for an altered pit initiation and nucleation behavior. These findings suggest that as the corrosion behavior is determined by the interplay of the chemical and electronic properties, only a mild anodic polarization in the presence of redox-active molecules is able to alter the chemical and electronic structure of the passive film formed on stainless steel AISI 304. This helps to achieve a profound understanding of the mechanisms of microbially influenced corrosion (MIC) and especially the possible effects of the redox-active biomolecules, as they may play an important role in the corrosion susceptibility of stainless steel surfaces.     

Some scientific considerations on the article: ‘Scientific basis for corrosion of copper in water and implications for canister lifetimes’ published by F. King and C. Lilja

Abstract

There has for the past 30 years been a debate regarding whether corrosion of copper can occur in anoxic water. In short the debate has been between experiments showing that corrosion of copper can occur and theory that predicts that it will not occur. The thermodynamics of copper corrosion, particularly, that copper cannot corrode in anoxic water, is a fundamental prerequisite for the Swedish repository concept for spent nuclear fuel developed by the Swedish Nuclear Fuel and Waste Management Company (SKB). Thus, in 1986 and subsequently Hultquist and co-workers experimentally confirmed that corrosion of copper can occur in some conditions. However, this research is generally assumed to be incorrect, most recently by a paper by King and Lilja in this journal. In this article I will develop the argument that Hultquist’s work should not be so disregarded.     

Design of hole-clinching process for joining of dissimilar materials – Al6061-T4 alloy with DP780 steel,hot-pressed 22MnB5 steel,and carbon fiber reinforced plastic

The mechanical joining of dissimilar materials is a key technology in the automotive industry as it enables the realization of car bodies that incorporate multiple materials. However, it remains difficult to join materials such as aluminum alloy to high-strength/low-ductility materials such as advanced high-strength steel, hot-pressed steel, and carbon fiber reinforced plastic by using joining methods that are based on forming technology. The purpose of this study is to develop a new joining process, called “hole clinching,” for these material combinations. In the hole-clinching process, the ductile material is positioned uppermost and the brittle material—into which a hole is formed—is positioned below that. The upper sheet is indented into a die cavity through the hole in the lower sheet and spread so that the two sheets interlock geometrically. In this study, hole-clinching tools were designed based on the geometrical relationship between the forming volume and the joint strength. Finite element analysis and practical experiments were performed to verify the practicality of the hole-clinching process. The cross-sections of the hole-clinched joints formed in our experiments were in good agreement with the results of the finite element analysis. Then, a single-lap shear test was performed to evaluate the joint strength. The hole-clinched joints, regardless of the material combinations, provided a joint strength in excess of the desired 2.5 kN. These results point to the applicability of the hole-clinching process to the joining of dissimilar materials.     

Synergistic inhibition effect of N-(furan-2-ylmethyl)-7H-purin-6-amine and iodide ion for mild steel corrosion in 1 mol/L HCl

The synergistic inhibition effect of N-(furan-2-ylmethyl)-7H-purin-6-amine (FYPA) and iodide ion on mild steel corrosion in 1 mol/L HCl was investigated using weight-loss tests, electrochemical techniques, and surface analysis. The experiments revealed that the FYPA + KI mixture was a temperature-dependent inhibitor, which strongly inhibited the corrosion of mild steel compared with FYPA. Based on electrochemical results, FYPA and FYPA + KI behaved as mixed-type inhibitors, and their inhibition efficiencies were 73.66% and 96.01%, respectively. The calculated synergistic parameter value was larger than unity, illustrating that enhancement of inhibition in the presence of KI could be a result of synergistic action. Surface analysis techniques (scanning electron microscope/scanning electrochemical microscope) confirmed the presence of additives on the studied mild steel surface. A plausible mechanism of corrosion inhibition was proposed.     

Corrosion behaviours of typical metals in molten hydrate salt of Na2HPO4·12H2O – Na2SO4·10H2O for thermal energy storage

ABSTRACT

The corrosion behaviours of stainless steel 316 (SS-316), copper (Cu) and aluminium 1060 (Al-1060) in composite molten hydrate salt phase change materials (PCM) composed of Na₂HPO₄·12H₂O – Na₂SO₄·10H₂O have been studied by electrochemical measurements in conjunction with SEM and XRD. The corrosion resistance of the metals in the composite molten PCM follows SS-316?>?Cu > Al-1060. The role of the composite molten PCM affecting the corrosion resistance and its mechanisms of the metals are as following: the experiments reveal that SS-316 readily gets passivated in the composite molten PCM medium with no considerable corrosion; Cu suffers an initial rapid anodic dissolution which is further impeded by the formation of spot-like salt precipitates on the substrate, mainly consisting of CuHPO₄·nH₂O, CuSO₄·nH₂O and Cu₂O; Al-1060 shows a continuous large dissolution in the studied PCM with a porous corroded surface morphology due to the complete destruction of passive film under the attack of OH^- ions.     

Potentialities of Raman Imaging for the Analysis of Oxide Scales Formed on Zircaloy-4 and M5® in Air at High Temperature

Micro-Raman imaging was used to investigate oxide scales formed on Zircaloy-4 and M5^® alloys in air, in the 800–1,000 °C temperature range. To create the 2D spectral images, the data were processed by different ways. The results clearly show that a microscopic picture of the scales in terms of microstructure and internal stresses can be developed from Raman spectral maps at the micron scale. Data on the microstructure, crystallography, and composition, are presented. They confirm that the crystallographic phases observed for the Zircaloy-4 and M5^® alloys are different, since, for Zircaloy-4, we clearly observed additional Raman signatures which most probably track the presence of nitrogen in the layers well before the occurrence of the kinetic transition. In particular, they show the presence of cubic zirconia in the layers, and strongly suggest the presence of zirconium nitride and oxynitride. Results also suggest the presence of strong stress gradients in the oxide scales.     

Aluminizing and boroaluminizing treatments of Mar-M247 and their effect on hot corrosion resistance in Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>−NaCl molten salt

The effect of surface modifications of Mar-M247 superalloy on hot corrosion resistance was examined in Na₂SO₄−NaCl molten salt. The Mar-M247 was aluminized and boroaluminized by pack cementation in Ar and underwent a cyclic hot corrosion test in Na₂SO₄−NaCl molten salt. The XRD results showed that a Ni₂Al₃ phase was formed between the aluminized layer and the substrate when the surface modification temperature was below 1273 K. However, a NiAl phase formed when the temperature was above 1273 K. The intensity of the XRD peak in the NiAl phase increased after post heat treatment. Hot corrosion resistance increased for the specimens containing NiAl rather than Ni₂Al₃ phase. The ductile NiAl phase suppressed the potential for crack initiation during thermal cycling. Post heat treatment increased the corrosion resistance of the aluminized layer for Mar-M247, which underwent surface modification at 1273 K and above. In the boroaluminized Mar-M247 specimens, corrosion resistance decreased as a result of the blocking of outward diffusion of Cr by boron and decreased cohesion between the oxide scale and the aluminized layer during thermal cycling.     

A study on the influence of the sloped cutting angle on kerfwidth and part quality in the hotwire cutting of EPS foam for the VLM- rapid prototyping process

The VLM- rapid prototyping process employs hotwire cutting of an EPS foam sheet using a four-axis synchronized automatic hotwire cutter. The dimensional accuracy and the quality of the cut part are highly dependent on cutting parameters such as effective heat input, and cutting angle, etc. The objective of this study is to investigate the influence of cutting angle on the kerfwidth and the part quality in hotwire cutting of EPS foam for the case of the sloped cutting including single-sloped cutting with one cutting angle and generally sloped cutting with two cutting angles. Experiments are carried out to obtain the relationship between kerfwidth and effective heat input for each cutting angle, and to find the relationship between the melted area and the cutting angle for each effective heat input. In order to investigate the influence of cutting angle on temperature distribution in EPS foam, transient heat transfer analysis using the sloped heat flux model and the conformed mesh structure is carried out. Through comparison of the results of the experiment and the transient heat transfer analysis, it has been shown that the sloped heat flux with an elliptical cross-section and the conformed mesh structure are needed to estimate the three-dimensional temperature distribution in the EPS foam in the sloped hotwire cutting.