Influence of copper on amorphous nickel based brazing alloy

Abstract

Brazing of stainless steel using nickel based alloys has sometimes been avoided, in spite of its various advantages, because it is a somewhat unreliable process in terms of the mechanical characteristics and corrosion resistance of the brazed joints. Addition of copper to amorphous Ni–Cr–B–Si brazing alloys has been shown to be a promising method of improving the performance of joints. Because copper can form a solid solution with nickel at any concentration, addition of copper has a great effect on the microstructures of the nickel based filler metal and braze seam, by improving the volume ratio of nickel based solid solution to the embrittled intermetallic compounds. As a result, a significant increase in the critical brazing clearance (CBC) was obtained in the present work. Furthermore, copper might increase the electrode potential of nickel based solid solution, so that addition of copper could improve the corrosion resistance of the brazed joints. The results show that an appropriate copper addition to the present Ni–Cr–B–Si group amorphous brazing foil provides an effective method of overcoming the weaknesses of joints brazed using conventional nickel based filler metals, such as low value of CBC and low corrosion resistance.     

Oxidation Mechanisms of Copper and Nickel Coated Carbon Fibers

Differential-Thermal Analysis (DTA) and X-ray diffraction analysis were applied to determine the mechanisms of high-temperature oxidation of copper- and nickel-coated carbon fibers. Both kinds of coatings were deposited by electroless plating onto the fiber surface. The as-deposited copper film was crystalline, whereas the nickel coating consisted of an amorphous Ni–P alloy. Coated fibers were heated from room temperature to 900 °C in air at 10 °C min^?1. For the copper coating, the main oxidation product formed at low temperatures was Cu₂O, while at higher temperatures was CuO. The crystallization of Ni–P took place at 280–360 °C with the formation of Ni and Ni₃P. The final compounds were NiO, Ni₂P and Ni₃(PO₄)₂. After complete oxidation of the carbon fibers, copper and nickel-oxidized microtubes were obtained. Besides, while copper reduced the temperature of the fiber oxidation, nickel coatings increased the minimum temperature needed for this reaction.     

Cu-15Ni-15Ag合金在600～700℃空气中的氧化

研究了Cu-15Ni-15Ag合金在600～700℃空气中的氧化 .合金由富Ag的α相与Cu-Ni固溶体β相组成;氧化速率基本服从抛物线规律,合金的成膜速 率与纯Cu氧化近似.不同温度下合金均形成了最外层为CuO,内层为Cu2O,NiO以及Ag颗粒 组成的复杂氧化膜.在700℃氧化时观察到典型的Ni的内氧化,同时,由于Ni优先溶解于CuO 中影响了CuO-Cu2O氧压平衡,导致形成了CuO位于Cu2O下的特殊氧化膜结构.     

Kinetic and morphological development of coke formation on heat-resistant alloys

The deposition of coke from a propylene-hydrogen mixture on to a range of austenitic Fe-Cr-Ni base alloys has been compared with deposition on pure nickel and pure copper. Nickel was catalytic to coking at temperatures below 900 °C, but at higher temperatures became encapsulated by pyrolytic coke. Copper showed no catalytic activity at any temperature in the range 600–1000 °C, and was instead covered with carbon deposited by homogeneous gas phase pyrolysis. Heat-resistant alloys formed pyrolytic coke at the same rates as copper and nickel at high temperatures, but displayed coking rates between those of the pure metals at lower temperatures. The alloys formed a chromium-rich carbide layer on their surface. This layer was initially protective, but eventually developed defects from which coke filaments grew. The formation of these filaments was catalysed by the chromium-depleted metal which became accessible to the gas following failure of the carbide layer. Once catalytic coke formation commenced, it was maintained by the presence within the coke of small metal particles rich in iron and nickel. The addition of steam to the gas slowed pyrolytic coking slightly through gas phase dilution. In the case of heat-resistant alloys, catalytic coking was largely suppressed by the formation of a surface scale containing chromium carbide and oxide. This scale was noncatalytic and was more successful than a simple carbide scale in preventing gas access to the underlying metal.     

Determination of Oxygen Diffusion Along Nickel/Zirconia Phase Boundaries by Internal Oxidation

Internal oxidation tests with nickel alloys that contained up to 8 at.% zirconium were carried out. All alloys were two-phase consisting of γ-Ni and the intermetallic phase Ni₅Zr. Their behavior under low oxygen partial pressures in the range of 800–1,000?°C could not be described by the Wagnerian analysis. Oxygen diffusivity along the interface nickel/monoclinic zirconia plays an important role for the rate of internal oxidation. The early stages of internal oxidation show the in situ mode where diffusion of the less noble element zirconium cannot diffuse in the matrix and is oxidized instantly. Later in the process the mode shifts from in situ towards the diffusive mode as zirconium has the possibility to diffuse. This change could also be observed as the size of the oxide particles varied with ongoing oxidation. A method for the determination of the oxygen diffusivity in nickel/monoclinic zirconia phase boundaries is presented.     

3DOM材料在汽车尾气净化催化剂中的应用前景

贵金属因其独特的催化性能,在车用尾气净化催化剂行业倍受关注。简述了当前贵金属催化剂的研究现状及存在的不足,并从三维有序大孔材料(3DOM)的特殊结构特征着手,阐述了3DOM催化净化作用的特点和优势。为高催化活性和低制造成本的新型贵金属三维有序大孔材料的研制和应用提供可行性分析。     

Growth of nanowires on the surfaces of multicomponent oxide coatings on titanium

The thermal behavior of Ni- and Cu-containing coatings on titanium formed by plasma electrolytic oxidation and additionally modified with nickel and copper oxides is studied. Annealing of the produced multiphase coatings in air at a temperature of 750°C or higher is shown to result in the growth of surface nanowires, the main components of which are nickel, oxygen, and titanium. The sizes of nanowires depend on the temperature of annealing, and the diameters can be as large as tens or hundreds of nanometers at a length of several to tens of microns. Experimental and literature data show that the combination of plasma electrolytic oxidation with impregnation and annealing is promising for the production of both nanowires bound to metal-oxide substrates and individual nanostructures of certain compositions.     

On the use of the micromarker technique for studying the growth mechanism of thin oxide films

The high temperature behavior of microscopic markers, deposited on to pure and ceria-coated nickel, was tested. The markers, having a form of 20-nm-thick palladium bumps with a fractional surface coverage of 0.05 and 30-nm thick gold bumps with a surface coverage of 0.25, apparently interfered with the oxide growth, increasing the oxidation rate on their surface at 973 K over one order of magnitude. As detected by a combination of Auger electron spectroscopy and Rutherford backscattering spectrometry, for ceria modified nickel, the markers’ depth-position coincided with the ceria particles dispersed in the vicinity of the oxide–gas interface. For pure nickel oxide films, the markers were easily incorporated into the growing oxide during very early stages of oxidation and were difficult to detect at the oxide–metal interface. It is proposed that the catalytic behavior of the markers was caused by their fragmentation into a large number of islands, leading to the refinement of the oxide grains, which in turn accelerated the substrate oxidation rate. Some precautions necessary in conducting the marker experiments are defined.     

Some factors influencing the adherence of oxides on metals

Some of the differences in adherence behaviour may be explained by differences in the respective physical properties of the films and the metals. The strength and plasticity of some of the oxides has been measured; the relative expansion coefficients are also important and it is thought to be the favourable nature of this which is responsible for the good adherence of NiO on nickel and more complex films on nickel-base alloys. Another important factor is internal stress. The sources of stresses during the oxidation of copper have been estimated using a unilateral oxidation technique. With sufficient knowledge of the mechanical properties it is possible to calculate the actual stress levels in the growing oxide film. A further factor influencing adherence is the accumulation of trace or residual elements on the metalloxide interface. The technique of Peters and Engell has been used to estimate the effect of various elements at a concentration of 0.4 wt% on the adherence of scales on iron. The results fall into four groups; those that form mixed oxide scales with wüstite either spalled or were weakly adherent; those on noble metal alloys were nearly comparable with pure iron, but copper and tin had a detrimental effect. Scales containing As, Sb and P were weakly adherent but left a thin adherent layer on the metal surface. Cobalt and niobium had no effect.     

贵金属核壳纳米粒子最新研究进展

贵金属核壳纳米粒子具有独特的光、电和催化性质,使其在材料科学、生物物理、分子电子学以及基于表面增强效应的荧光工程学领域具有极其广泛的应用前景.本文综述了贵金属核壳纳米粒子的制备方法及应用,并对贵金属核壳材料的发展进行了展望.     

The oxidation of cupro-nickel alloys—II. The kinetics of diffusion in porous inner layers

The oxidation of cupro-nickel alloys at temperatures > 160°C produces a duplex oxide structure. In Part I, diffusion of copper across the inner nickel oxide layer was shown to be rate controlling. This conclusion is tested in this paper by examining the oxidation rate curves of a series of nine metals and alloys extending from pure copper to pure nickel. The isochronal curves are found to pass through a maximum at 75%Cu which is explained by surface diffusion of the copper through a porous nickel oxide structure extending through the metal consumption zone. The surface diffusion coefficient derived from this model is in the range 0.8–2.0 × 10^?14 m² s^?1 in accord with results of other workers.     

贵金属阳极材料的应用与研究进展

贵金属阳极材料具有优异的电催化性能,为提高其催化活性,节能减耗减少其用量人们做了大量的研究。基于近十年来50余篇文献的分析,本文综述了贵金属阳极材料在基础化学工业的广泛应用及研究现状。展示了不同贵金属阳极的特点、发展历程和应用领域。介绍了贵金属氧化物阳极在电解水、氯碱工业、工业催化和废水处理等方面的应用进展,讨论了阳极材料的载体、控制形状、组成与物理化学特征之间的关系。对贵金属阳极材料的进一步发展及合理设计进行了展望。     

Effect of the structure of the oxidized titanium surface on the particle size and properties of the deposited copper–molybdate catalyst

The parameters of wetting of oxide coatings on titanium formed by the method of plasma electrolytic oxidation (PEO) in an aqueous silicate electrolyte with subsequent deposition of a layer of TiO₂ nanoparticles and ultrasonic treatment by a polymer–salt gel including copper and molybdenum compounds have been investigated. The effect of the oxidized surface microrelief, TiO₂ nanoparticle layer, and pore shape and size on impregnation solution spreading and the structure of the copper–molybdenum catalytic coating formed at further thermal treatment has been demonstrated. Complex oxide composites with ultradispersed catalyst particle sizes characterized with high activity in oxidation of carbon black particles have been obtained.     

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.     

Microbially influenced corrosion and inhibition of nickel–zinc and nickel–copper coatings by Pseudomonas aeruginosa

The present study describes the effect of Pseudomonas aeruginosa on the corrosion rate of nickel–zinc and nickel–copper alloy coatings. The presence of bacteria was associated with decreases in R_ct values, suggesting that P. aeruginosa promoted the corrosion of nickel–copper alloy coatings. However, R_ct values of nickel–zinc coatings increased in response to bacterial inoculation, corresponding to a decrease in corrosion rate for nickel–zinc alloy coatings. Our results suggest that the activity of P. aeruginosa facilitated the corrosion of nickel–copper alloy, while serving a protective function for the nickel–zinc alloy.     

Oxidation Potentials in Iron and Steel Making

The state of oxidation of a pyrometallurgical process given by the partial pressure of oxygen and the temperature (the oxidation potential) is one of the important properties monitored and controlled in the smelting and refining of iron and the nonferrous metals. Solid electrolyte sensors based on ZrO₂ and a reference electrode such as Cr/Cr₂O₃ to measure the oxygen pressure found early application in the steel industry, followed soon after in copper, nickel, lead, and zinc smelting. Similar devices are installed in automobile postcombustion/exhaust trains as part of emission control systems. The current discussion reviews this technology as applied in the primary steps of iron and steel making and refining.     

Filiform corrosion of binary aluminium model alloys

The effect of alloy composition and microstructure on filiform corrosion (FFC) susceptibility was investigated for super-purity based binary model alloys of the systems Al-Mg, Al-Mn, Al-Fe and Al-Cu. Corrosion testing indicated that the presence of electrochemically noble second phase particles is a necessity for FFC to occur. Single phase, solid solution alloys of the Al-Mg, Al-Mn or Al-Fe systems did not support FFC. Heat treatment caused precipitation of the electrochemically noble intermetallic phase FeAl₃ in the Al-Fe alloy, resulting in extensive FFC. Precipitation of the phase MnAl₆, which has electrochemical properties similar to that of the aluminium rich matrix, by heat treatment did not impair the corrosion properties of the Al-Mn alloy. Significant surface oxidation and magnesium enrichment of the surface oxides by heat treatment did not affect the FFC properties of Al-Mg alloys. However, the solid solution binary Al-Cu alloys exhibited severe FFC. The detrimental effect of copper in solid solution is attributable to selective dissolution phenomena during the corrosion process, whereby copper was locally enriched on the surface as copper-rich particles providing efficient cathodic sites.     

硫酸介质中氯化物参与下氧化浸出铜渣过程

研究了镍铳选择性氧化浸出产生的铜渣在硫酸介质中氯离子参与下的氧气氧化浸出,考察和比较了氯化物用量、氧气流量、硫酸浓度、温度等因素对铜和镍浸出的影响,并讨论了其原因,确认了在硫酸介质中加入少量氯化物即可在常压下用氧气有效地浸出主要由辉铜矿或类似的硫化铜矿物组成的铜渣。     

Electrodeposition of Copper-Nickel Alloys from a Citrate Bath Containing Boric Acid

Copper-nickel alloys have been electrodeposited on steel substrates from a bath containing copper sulphate, nickel sulphate, sodium sulphate, sodium citrate and boric acid. Galvanostatic cathodic polarization, cathodic current efficiency and composition of the alloys were studied as influenced by bath composition, current density and temperature.

The bath is characterized by high cathodic current efficiency. Current density is found to strongly influence the composition of the deposits. At low current densities (lower than a certain transition current density), a copper-rich alloy is deposited with copper (the more noble metal) being the preferentially deposited metal. At larger current densities, nickel becomes the nobler metal and is deposited preferentially. The magnitude of the transition current density depends upon the bath composition and temperature. The structure and surface morphology of the as-deposited alloys were examined by XRD and SEM. The results reveal the presence of a single solid solution phase with face centred cubic structure. The morphology of the deposits is mainly controlled by the alloy composition.     

Role of additives in electroless copper plating using hypophosphite as reducing agent

In electroless copper plating baths using hypophosphite as the reducing agent, nickel ions was used to catalyze hypophosphite oxidation. However, the color of the copper deposits was dark or brown and the electrical resistivity was much higher than that obtained from formaldehyde baths. Polyethylene glycol (PEG) and K₄Fe(CN)₆ were used to improve the microstructure and properties of copper deposits obtained from electroless copper plating bath using hypophosphite as the reducing agent. The effects of PEG concentration on the deposition rate, the microstructure, morphology and electrical resistivity of the copper deposits, and the electrochemical reactions of hypophosphite (oxidation) and cupric ion (reduction) were investigated. The traces of hydrogen escaping from the deposits surface disappeared and the color of the copper deposits changed from dark-brown to dark red when the PEG concentration was 1.67 × 10^− 5 M or more. The deposition rate increased and the electrical resistivity of the copper deposits decreased slightly with the addition of PEG to the plating solution. The electrical resistivity of copper deposits decreased to 2.85 μΩ cm with 1.67 × 10^− 5 M PEG and 4.70 × 10^− 6 M K₄Fe(CN)₆ in the bath. Larger grain size and higher (220) plane orientation were obtained with the increase of PEG concentration in the bath. The electrochemical current–voltage results showed that PEG accelerated the catalytic oxidation of hypophosphite at active nickel sites and had little effect on the reduction reaction of cupric ions on the deposit surface by adsorption on the electrode.