Corrosion behaviour of experimental copper–antimony–molybdenum carbon steels in industrial and marine atmospheres and in a sulphuric acid aqueous solution

Low alloyed carbon steels are used in several applications as in automotive, home appliances and civil industries. Sb-bearing steels have been developed to withstand acid condensation, mainly to exhibit corrosion resistance to sulphuric acid aqueous solutions. This work is aimed at studying the corrosion resistance of three experimental low alloyed carbon steels with additions of copper, antimony and molybdenum using the electrochemical impedance spectroscopy (EIS) in a sulphuric acid aqueous solution, and field tests in industrial and marine atmospheres. The field tests showed the mass loss of antimony–molybdenum carbon steels was higher compared to that of other steels. The alloyed carbon steels with copper and antimony additions showed the highest atmospheric corrosion resistance evaluated by using field tests in industrial and marine environments. The molybdenum-bearing steels showed the highest corrosion resistance in a sulphuric acid solution, measured by using the EIS.     

The improvement of high-temperature oxidation of Ti–50Al by anodic coating in the phosphoric acid

The high temperature cyclic oxidation resistance of Ti–50Al can be improved by anodic coating in phosphoric acid aqueous solution (4 wt% H₃PO₄) at 18°C. Sparking occurs sporadically on the surface as the voltage is over 300 V and the instantaneous current density after 45 min of anodization increases with increasing voltage. The anodic films are amorphous and contain substantial amount of phosphorus. Cyclic oxidation test indicates that the anodization can remarkably reduce the oxidation in air at 800°C and the improvement increases with increasing anodizing voltage up to 400 V, at which the parabolic oxidation rate constant can be reduced to about 1/600 of that for as-homogenized Ti–50Al. Raman spectra show that the anodic film can slow down the formation of rutile and α-Al₂O₃ during oxidation. The doping effect of phosphorus ions in titanium oxide accounts for the improvement of high temperature oxidation of Ti–50Al.     

Defects caused by precipitation of in liquid copper–nickel–aluminium–bronze alloys dissolved carbon and removal by treatment of melt

Castings made of copper–nickel–aluminium bronze (CuAl₁₀Fe₅Ni₅) alloys regularly show defects in the thick, slowly solidifying parts of the castings, which give rise to rejections. Metallographic examination has been made on material of scrap castings showing porosity accompanied with film-like inclusions located beside the iron rich κ_II phases. Investigations of large failed cast structures of copper–nickel–aluminium bronze show the same characteristic defects on which fatigue cracks initiate and grow. Investigation has been made to the nature and the cause of appearance of the film-like inclusions. Microanalysis indicates a high intensity of carbon at the place of the film-like inclusions. Hereafter, an investigation has been made into the solubility of carbon in liquid copper–nickel–aluminium bronze, and it is found that besides hydrogen, also carbon is soluble in copper–nickel–aluminium bronze alloys. The appearance of the carbon as flakes in the fracture surface of materials with defects does suspect there is a nucleating effect on the formation of microporosity causing the defects. To prevent the formation of the casting defects by the interaction between solved hydrogen and carbon, it is necessary to remove the carbon as far as possible by treatment of the melt.     

Corrosion fatigue behavior of epoxy-coated Mg–3Al–1Zn alloy in NaCl solution

The corrosion fatigue behavior of epoxy-coated Mg–3Al–1Zn alloy was investigated in air and 3.5 wt%NaCl solution. Epoxy coating as a new method was used to improve the corrosion fatigue property of the material.Results show that the fatigue limit(FL) of the coated specimens is higher than that of the uncoated specimens in3.5 wt% NaCl solution because of the strengthening and blocking functions of the epoxy coating. The FL of the coated specimens in 3.5 wt% NaCl solution is as high as that in air. It implies that the coated specimens are not as sensitive to the environment as the magnesium alloy. The low tensile strength and the short elongation of the pure epoxy coating lead to that the fatigue crack of the coated specimen is always initiated from the epoxy-coating film Pores and pinholes accelerate the fatigue crack initiation process. Pinholes are caused by the corrosion reactions between the epoxy coating and the NaCl solution.     

Growth of η phase scallops and whiskers in liquid tin-solid copper reaction couples

In the microelectronics industry, many solder junctions rely upon reaction between a copper substrate and a molten tin-based alloy. For the tin/copper system, interfacial continuity is afforded by the formation of the η (Cu₆Sn₅) and ɛ (Cu₃Sn) phase intermetallic compounds. The η grows in a scalloped morphology along the tin interface with whiskers emanating from their tops. This article quantitatively describes the unusual growth behavior of the η phase scallops and whiskers formed during reaction of liquid tin with a solid copper substrate. For more information, contact R. Gagliano, Northwestern University, Department of Materials Science, 2225 N. Campus Drive, Evanston, Illinois 60208; e-mail r-gagliano@northwestern.edu.     

Electrochemical behavior of Cu(II) reduced in CH3OH and DMSO

The cyclic voltammetry and the potential-time curve after galvanostatic electrolysis were used to study the electrode processes of Cu(n) in CH3OH solution and DMSO solution. The electroreduction of Cu(Ⅱ) to Cu on a Pt electrode proceeds in two steps: Cu(Ⅱ) + e = Cu(Ⅰ); Cu(I) + e = Cu. The reduction potential of Cu(n) in DMSO solution is more negative than that in CH3OH solution, and the diffusion coefficient of Cu(Ⅱ) ion in DMSO solution is larger than that in CH3OH solution because the polarity of DMSO is larger than that of CH3OH observably and has a stronger solvating power.     

Electrodeposition of palladium films from ionic liquid (IL) and deep eutectic solutions (DES): physical–chemical characterisation of non-aqueous electrolytes and surface morphology of palladium deposits

Abstract

The physical and electrochemical characteristics such as density, viscosity, electrical conductivity and cyclic voltammetry of three different non-aqueous palladium electrolytes were analysed. The cyclic voltammetry behaviour showed typical reduction and oxidation peaks corresponding to the deposition and stripping of palladium in the electrolytes employed. The electrodeposition of palladium films from choline chloride/ethylene glycol (ChCl-EG), choline chloride/urea (ChCl-urea) and 1-butyl-3-methylimidazolium chloride-tetrafluoroborate (BMIM-Cl-BF₄) solutions was demonstrated. Compact deposits were obtained with galvanostatic electrolysis. The scanning electron micrographs of the deposits revealed predominantly nodular Pd particles.     

Preparation of REPO_4(RE=La–Gd) nanorods from an ionic liquid extraction system and luminescent properties of CePO_4:Tb~(3+)

Uniform nanorods of rare earth phosphate(REPO_4, RE = La–Gd) nanocrystals were prepared in a properly designed ionic liquid extraction system by a stripping precipitation method. Rare earth ions were extracted into the organic phase at first; after that, the loaded organic phase was stripped by aqueous solution of PO_4~(3-) under stirring at room temperature within 5 min.The extractant used here is a bifunctional ionic liquid extractant called [A336][cyanex272]. The products are hexagonal phase in crystal structure, and their morphology is nanorods. The diameter of the products is from 30 to 50 nm, and the length increases from 200 nm to 2 μm gradually. Besides, the ionic liquid-absorbed CePO_4:Tb~(3+) nanorods show improved luminescent emitting intensity and lifetime. Based on the results, a possible growth mechanism of the REPO_4(RE = La–Gd) nanorods is proposed, where the extractants here also play roles of structure-directing agents and surfactants during the formation process of nanocrystals.     

Effect of short-circuiting on the oxidation kinetics of copper and its doped varieties in the temperature range of 523–1073 K

The influence of shorting circuitry attachment between metal-oxide and oxideoxygen interfaces on the oxidation kinetics of copper, lithium-doped copper (Li: 400 ppm), and chromium-doped copper (Cr: 12 ppm) have been studied in dry air in the temperature range of 523–1073 K. Oxide film or scale growth under short-circuiting as well as under normal oxidation conditions conforms to the parabolic rate law. The oxidation kinetics under short-circuiting resulted in decreased rates for Cu and Li-doped Cu up to a temperature of 773 K, while Cr-doped Cu exhibited an enhancement in rate compared to its normal oxidation in the same temperature range. However, above 873 K, all three systems under shorting circuitry attachment exhibited enhanced rates compared to their normal oxidation rates in conformity to the existing theoretical model. Use of additional resistances in series in the outer short-circuit Pt path have clearly established that below 773 K Mott's fieldinduced migration plays the most important role, while at elevated temperatures Wagner's electrochemical potential-gradient factor acts as the main driving force in the scale-growth process. The results have been interpreted on the basis of average defect concentration, the electrochemical potential gradient, electrical field gradient, and transport coefficient in the Cu₂O layer.     

Shape memory properties and oxidation behaviour of a rapidly liquid quenched Cu–Sn alloy

Rapidly liquid quenched Cu–Sn ribbons were produced and their shape memory properties and oxidation behaviour investigated using thermal analysis, metallography and X-ray diffraction methods. During the heating regime from −70°C to room temperature in a DSC instrument, martensite → austenite transformation was performed and the A_s and A_f temperatures were determined as −16.4°C and −8.4°C respectively. The oxidation behaviour was also determined using TGA. The total oxidation percentages decreased with increasing heating rate, whereas the oxidation rate increased with the heating rate during the heating and cooling times. The shape memory behaviour of the ribbon samples were also seen after bending in liquid nitrogen and reheating to room temperature.     

Structure and oxidation resistance of W1–xAlxN composite films

A series of W_1–xAl_xN films (0<x<38.6%, mole fraction) were deposited by reactive magnetron sputtering. The composition, microstructure, mechanical properties and oxidation resistance of the films were characterized by EPMA, XRD, XPS, nano-indentation, SEM and HRTEM. The effect of Al content on the microstructure and oxidation resistance of W_1–xAl_xN films was investigated. The results show that WN film has a face-centered cubic structure. The preferred orientation changes from (111) to (200). The W_1–xAl_xN films consist of a mixture of face-centered cubic W(Al)N and hexagonal wurtzite structure AlN phases. The hardness of the W_1–xAl_xN films first increases and then decreases with the Al content increasing. The maximum hardness is 36 GPa, which is obtained at 32.4% Al (mole fraction). Compared with WN film, the W_1-xAl_xN composite films show much better oxidation resistance because of the formation of dense Al₂O₃ oxide layer on the surface.     

Corrosion behaviour of Cu–2Ti and Cu–2Zr (wt%) alloys in neutral aerated sodium chloride solution

The corrosion behaviour of Cu–2Ti and Cu–2Zr (wt%) alloys has been assessed by open-circuit potential and electrochemical impedance spectroscopy measurements carried out in 3.5 wt% NaCl solution, at approximately neutral pH, without stirring and in contact with the air. For comparison, the electrochemical tests have also been carried out on unalloyed Cu. Electrochemical impedance results showed that Ti and Zr alloying additions significantly increased the corrosion resistance of copper, the best behaviour being observed for the Cu–2Zr alloy. This improvement may be ascribed to the formation of Ti- or Zr-enriched passive layer, which exhibits higher protective effectiveness compared with that of unalloyed Cu.     

The structure of molten zones in explosion welding (aluminium–tantalum,copper–titanium)

Investigations were carried out into the relief of the flat- and wave-shaped interfaces for explosion-welded aluminium–tantalum and copper–titanium welded joints. For these systems, characterized by a relatively high mutual solubility of the initial elements, the results show a typical set of the structures of the interfaces replacing each other with the intensification of the welding conditions. The unusual shape of the projections on the flat interfaces was found. They are similar to splashes, which form on the surface of the liquid, although they are solid-phase splashes. The vortex structure of the zones of local melting was also detected. The unusual shape of the waves was found: in the presence of mutual solubility they consist of the specially ordered set of projections. It may be assumed that this is caused by the formation of intermetallic compounds on the surface of the projections. The processes of self-organization, ensuring the evolution of the relief of the interface in the intensification of the welding conditions, have been investigated. The role of intermetallic compounds in these self-organization processes is clarified.     

A comparative study of microstructure,oxidation resistance,mechanical, and tribological properties of coatings in Mo–B–(N), Cr–B–(N) and Ti–B–(N) systems

M–B–(N) (M = Mo, Cr, Ti) coatings were obtained by the magnetron sputtering of MoB, CrB₂, TiB, and TiB₂ targets in argon and in gaseous mixtures of argon with nitrogen. The structure and composition of the coatings have been investigated using scanning electron microscopy, glow-discharge optical emission spectroscopy, and X-ray diffraction. The mechanical and tribological properties of the coatings have been determined by nanoindentation, scratch-testing, and ball-on-disk tribological tests. The experiments on estimating the oxidation resistance of coatings were carried out in a temperature range of 600–1000°С. A distinctive feature of TiB₂ coatings was their high hardness (61 GPa). The Cr–B–(N) coatings had high maximum oxidation resistance (900°С (CrB₂) and 1000°С (Cr–B–N)) and possessed high resistance to the diffusion of elements from the metallic substrate up to a temperature of 1000°С. The Mo–B–N coatings were significantly inferior to the Ti–B–(N) and Cr–B–(N) coatings in their mechanical properties and oxidation resistance, as well as had а tendency to oxidize in air atmosphere after long exposure at room temperature. All of the coatings with nitrogen possessed a low coefficient of friction (in a range of 0.3–0.5) and low relative wear ((0.8–1.2) × 10^–6 mm3 N^–1 m^–1.     

Corrosion electrochemical mechanism ofchemical mechanical polishing of copper in K3Fe（CN）6 solution

1　ＩＮＴＲＯＤＵＣＴＩＯＮＣｈｅｍｉｃａｌ ｍｅｃｈａｎｉｃａｌ ｐｏｌｉｓｈｉｎｇ (ＣＭＰ )ｉｓｔｈｅｍｏｓｔｉｍｐｏｒｔａｎｔｇｌｏｂａｌｐｌａｎａｒｉｚａｔｉｏｎｔｅｃｈｎｏｌｏｇｙａｔｐｒｅ ｓｅｎｔ.Ｓｐｅｃｉａｌｌｙｔｏｐｏｌｉｓｈｉｎｇｏｆｍｅ     

Hydrothermal synthesis of titanium-supported nanoporous palladium–copper electrocatalysts for formic acid oxidation and oxygen reduction reaction

Nanoporous Pd and binary Pd-Cu particles were prepared by a hydrothermal method using ethylene glycol as a reduction agent and they were directly immobilized on Ti substrates named as Ti-supported Pd-based catalysts. Their electrocatalytic activity for formic acid oxidation and oxygen reduction reaction (ORR) in alkaline media was examined by voltammetric techniques. Among the as-prepared catalysts, nanoPd₈₁Cu₁₉/Ti catalyst presents the highest current density of 39.8 mA/cm² at ?0.5 V or 66.4 mA/cm² at ?0.3 V for formic acid oxidation. The onset potential of ORR on the nanoPd₈₁Cu₁₉/Ti catalyst presents an about 70 mV positive shift compared to that on the nanoPd/Ti, and the current density of ORR at ?0.3 V is 2.12 mA/cm², which is 3.7 times larger than that on the nanoPd/Ti.     

Corrosion characteristics of zinc–zirconium alloy in c-SBF and its biocompatibility in vitro/in vivo

Zinc-based metals have attracted attention as biodegradable implant materials for medical applications. New alloying systems are still being tried. In this study, three kinds of extruded zinc–zirconium alloys (R1, R2, and R3) were prepared, and two of the most important performance of corrosion characteristics and biocompatibility in vitro/in vivo were carefully examined. We found that zirconium content did not linearly influence the corrosion behavior. Zirconium improved the zinc–zirconium alloy corrosion potential, but the strengthening effect was weakened due to the ZrZn ₂₂ phase, leading to microgalvanic corrosion. The alloy with zirconium content of 0.8% (R2) showed high corrosion resistance and minimum initial corrosion rate in the corrected simulated body fluid. R2 alloy also exhibited favorable cytocompatibility and biological histocompatibility.     

Electrodeposition of ternary Zn–Ni–Sn alloys from an ionic liquid based on choline chloride and their characterisation

Ternary Zn–Ni–Sn alloy coatings with a range of compositions were potentiostatically electrodeposited on steel substrates from a deep eutectic solvent-based electrolyte. The effect of electrodeposition potential on the morphology, chemical and phase compositions, and corrosion behaviour of the deposits was analysed. The co-deposition mechanism of Zn–Ni–Sn alloys was found to be normal whereby increasing the electrodeposition potential enhanced the ternary alloy Zn content (active element) and greatly suppressed the alloy Sn and Ni content (noble elements). The X-ray diffraction phase analyses showed that Ni in the deposits exists in the form of metal compounds including β-Ni₃Sn₂ as well as γ-NiZn₃. The improved corrosion resistance observed in all ternary alloys was attributed to their compact morphology, phase content and chemical composition. Comparison of corrosion performances shows that ternary Zn–Ni–Sn alloys are superior for sacrificial corrosion protection of steel metallic substrates compared to binary Zn–Sn and Zn–Ni alloys.     

Corrosion Behavior of Ni–20Cr–18W–1Mo Superalloy in Supercritical Water

The corrosion behavior of Ni–20Cr–18 W–1Mo superalloy in supercritical water 500 °C/25 MPa for 200 h is investigated using gravimetry, SEM/EDS, XPS, and TEM. The oxide films show a layered structure with Ni rich in the outer layer, and Cr rich in the inner layer, consisting of an outer Ni(OH)2and NiO layer, including some Cr(OH)3, and an inner Cr2O3, Ni Cr2O4, and WO3 layer. Mo elements are not oxidized. The oxide films grow via a mixed mechanism,namely metal dissolution/oxide precipitation mechanism and solid-state growth mechanism. The effects of secondary and primary carbides on the weight-gain trend and oxide formation are discussed.