Dissolution Of Base Metal Research Articles

Transient liquid phase diffusion bonding of Al/Al2O3 nanostructured metal matrix composites

Transient liquid phase (TLP) diffusion bonding was carried out on nanostructured metal matrix composite sheets of Al-1100 alloy with 5 wt-% alumina particles at various bonding temperatures and process durations. A thin layer of 5 μm pure copper was electrodeposited as an interlayer. Joint formation was first attributed to the solid state diffusion of copper into the aluminium metal matrix followed by eutectic formation; then, base metal dissolution and isothermal solidification was completed at the joint interface. Joint area was characterised using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Diffraction patterns showed the formation of intermetallic phases like CuAl2. The concentration of Al2O3 particles increases across the interface as the bonding temperature increases. As a result, the highest bond strength of 123 MPa was achieved after a bonding duration of 30 min at 590°C.

Copper recovery and gold enrichment from waste printed circuit boards by mediated electrochemical oxidation

The present study aims to develop an eco-friendly chemical–electrochemical process for the simultaneous recovery of copper and separation of a gold rich residue from waste printed circuit boards (WPCBs). The process was carried out by employing two different types of reactors coupled in series: a leaching reactor with a perforated rotating drum, for the dissolution of base metals and a divided electrochemical reactor for the regeneration of the leaching solution with the parallel electrowinning of copper. The process performances were evaluated on the basis of the dissolution efficiency, current efficiency and specific energy consumptions. Finally a process scale up was realized taking into consideration the optimal values of the operating parameters. The laboratory scale leaching plant allowed the recovery of a high purity copper deposit (99.04wt.%) at a current efficiency of 63.84% and specific energy consumption of 1.75kWh/kg cooper. The gold concentration in the remained solid residue was 25 times higher than the gold concentration in the initial WPCB samples.

Transient liquid phase diffusion bonding for micro PCD tool fabrication

In this study, K30 (W 90 wt%, Co 10 wt%) and DX5 (W 84 wt%, Co 16 wt%) tungsten carbide were used as base metals for transient liquid-phase diffusion bonding (TLPDB). The filler metal was MBF20, a type of nickel alloy used to minimize the residual stresses that occur due to the differences in the expansion coefficients of the metals. MBF20 contained B, Si, and Cr, which reduced the melting point of the nickel alloy and enhanced its mechanical properties. The base metal and filler metal surfaces were cleaned by mechanical polishing and cleaning. Diffusion bonding was performed under vacuum at 1,000–1,500 K under low pressure than buckling load conditions. The microstructure on the localized bonded surface was analyzed using scanning electron microscope (SEM) and optical microscopy. Result of no significant change was observed in the diffusion bonding in the low-to-mid temperature range due to insufficient filler metal or base metal dissolution at the bonding site. However, at high temperatures, the filler completely melted and bonded to the base metal on both sides. Our results showed that temperatures approaching the recrystallization temperature were required to provide high-quality welds for ultra-precision joints and micro polycrystalline diamond (PCD) tool fabrication.

First melting stages during isothermal brazing, of Ni/BNi-2 couples

Ni/BNi-2 brazing couples were continuously heated at 25°C/min and their melting temperature range was determined by differential thermal analysis (DTA). Samples were cooled down from different temperatures in the melting domain. Their microstructures were observed and quantitatively characterized through image analysis. Melting proceeds in two steps: The first one (lower temperatures) involves the filler metal being only partially melted, and boron diffusion in pure Ni leading to the precipitation of fine Ni3B borides at the initial interface between the filler alloy and the base metal. In the second step (higher temperatures), melting completes and thermodynamic equilibration requires significant dissolution of nickel, which also involves the dissolution of the borides already formed. Afterwards, transient liquid bonding can proceed as described in the usual models, involving re-precipitation of Ni3B borides on the new fresh interface between liquid alloy and solid metal. High heating rates allow avoiding the first step (direct melting of brazing alloy then dissolution of base metal), whereas very low heating rates can result in brazing without significant dissolution of base metal (no second step).

Modelling of an autoclave used for high pressure sulphuric acid/oxygen leaching of first stage leach residue. Part 1: Model development

Pressure leaching of the first stage leach residue in Base Metal Refinery (BMR) circuits aims to achieve high base metal dissolution with minimal precious metal leaching. Optimum autoclave operation is challenging because of the complex leaching chemistry, varying mineralogy of the feed material, and interaction between the different process variables. This research involved the modelling of the pressure leaching stages with flash recycle cooling at a typical BMR. The steady state solution employed the sequential modular approach in MATLAB, while the dynamic simulation involved the simultaneous solution of a set of differential equations, derived from mass and energy balances, in MATLAB. Part I of this communication presents a discussion of the Western Platinum Ltd. BMR process, an overview of relevant literature, and the strategies followed to develop both a steady state model and a dynamic model. Part II of this communication discusses the application of the models.

Effect of Ni–Al2O3 nanocompositecoating thickness on transient liquid phase bonding of Al 6061 MMC

Transient liquid phase diffusion bonding of Al 6061 containing 15 vol.-%alumina particles was carried out as a function of interlayer thickness. ElectrodepositedNi coatings containing 18 vol.-% nanosized alumina particles with thicknessranging from 1 to 13 μm was used as the interlayer. Joint formation wasattributed to the solid state diffusion of Ni into the Al 6061 metal matrixbase metal followed by eutectic formation, base metal dissolution and isothermalsolidification at the joint interface. Examination of the joint region usingscanning electron microscopy, wavelength dispersive spectroscopy and X-raydiffraction showed the formation of intermetallic phases such as AlFe3Si,Ni17Al3·9Si5·1O48and Ni3Si within the joint zone. The results indicated that a maximumjoint strength of 92% of the base metal shear strength can be obtainedif an 11 μm thick Ni–Al2O3 nanocomposite coatingis used as the interlayer.

Nickel, copper and cobalt distribution and equilibria in Anglo Platinum furnace slags

Base metals (nickel, copper and cobalt) are recovered as part of the smelting and refining process operated by Anglo Platinum in South Africa. This study focuses on the losses of these metals to furnace slag and the effect of changing the furnace feed to include or exclude recycled oxidising converter slag. A combination of electron microbeam and Mössbauer techniques were used to characterise the base metal distribution in the slag, the variation of losses with depth in the slag bath, and the oxygen activity in the slag. Base metal dissolution into the slag is underestimated if bulk matte–slag equilibrium is assumed; predictions are closer to the observed extent of dissolution if equilibrium between entrained matte and slag is assumed, for oxygen activity controlled by the Fe3+(slag)/Fe2+(slag) or FeO(slag)/Fe(matte) buffers.

Mechanisms of Activity Loss in PtCo Alloy Systems

The mechanism of activity loss in Pt and PtCo alloy systems has been investigated during 0.6 - 1.0 V and 0.6 - 1.2 V vs RHE cycling regimes using an electrochemical cell that allows electrochemical metal area (ECA) loss measurement and electrolyte sampling. Dissolution of platinum and base metal into the electrolyte was quantified using ICP-MS and TEM used to look for changes in catalyst morphology with cycles. ECA loss and base metal removal were found to be potential dependent. PtCo alloys were found to be more stable to ECA loss by Ostwald-ripening and dissolution than Pt. In terms of base metal loss the PtCo alloy was unstable and cycling was found to remove similar amounts of Co by dissolution as chemical acid leaching. Loss of Co from the surface layers of the catalyst was found to remove the enhanced stability and activity benefits of this catalyst making it more platinum like.

Cleaning of waste smelter slags and recovery of valuable metals by pressure oxidative leaching

Huge quantities of slag, a waste solid product of pyrometallurgical operations by the metals industry are dumped continuously around the world, posing a potential environmental threat due to entrained values of base metals and sulfur. High temperature pressure oxidative acid leaching of nickel smelter slags was investigated as a process to facilitate slag cleaning and selective dissolution of base metals for economic recovery. Five key parameters, namely temperature, acid addition, oxygen overpressure, solids loading and particle size, were examined on the process performance. Base metal recoveries, acid and oxygen consumptions were accurately measured, and ferrous/ferric iron concentrations were also determined. A highly selective leaching of valuable metals with extractions of >99% for nickel and cobalt, >97% for copper, >91% for zinc and <2.2% for iron was successfully achieved for 20 wt.% acid addition and 25% solids loading at 200–300 kPa O 2 overpressure at 250 °C in 2 h. The acid consumption was measured to be 38.5 kg H 2SO 4/t slag and the oxygen consumption was determined as 84 kg O 2/t slag which is consistent with the estimated theoretical oxygen consumption. The as-produced residue containing less than 0.01% of base metals, hematite and virtually zero sulfidic sulfur seems to be suitable for safe disposal. The process seems to be able to claim economic recovery of base metals from slags and is reliable and feasible.

Effect of alloying elements on the isothermal solidification during TLP bonding of SS 410 and SS 321 using a BNi-2 interlayer

The random diffusion of solute atoms during transient liquid phase (TLP) bonding of SS 410 and 321 with nickel-based brazing filler alloy BNi-2 have been modeled using Random Walk Modeling technique. Cumulative probability distributions and probability density functions of isothermal solidification times have been calculated for different process conditions and verified with experimental data. The solubility limit of boron has been found to have decreased from 0.3 at.% at higher temperature bonding operations (1358–1394 K) because of substantial iron-rich base metal dissolution when SS 410 was used as base metals; whereas it remained unchanged for SS 321/BNi-2 combination because of high concentrations of nickel and chromium in the base metal. Silicon diffusion model, based on the EDS analysis, also predicted the isothermal solidification times reasonably well.

Improvement in Corrosion Properties of Carbon-coated Fe-based Metals for PEFC Bipolar Plate

Low cost metals are quite attractive as bipolar plate of polymer electrolyte fuel cell (PEFC). However, low cost metals easily corrode due to the absence of good passivation films. In order to give high electrical conductivity and corrosion resistance to low cost metals such as carbon steel (S25C), carbon-coat was carried out by plasma-assisted chemical vapor deposition. Carbon-coated samples were characterized by XRD, Raman spectroscopy, and interfacial contact resistance. Based on the results of polarization measurement, the combination of carbon-coat and electroless nickel plating was found to be effective for decreasing of anodic dissolution of base metal.

Corrosion resistant properties of polyaniline–acrylic coating on magnesium alloy

The performance of the paint coating based on acrylic–polyaniline on magnesium alloy ZM 21 has been studied by electrochemical impedance spectroscopy in 0.5% NaCl solution. The polyaniline was prepared by chemical oxidative method of aniline with ammonium persulphate in phosphoric acid medium. The phosphate-doped polyaniline was characterized by FTIR and XRD methods. Acrylic paint containing the phosphate-doped polyaniline was prepared and coated on magnesium ZM 21 alloy. The coating was able to protect the magnesium alloy and no base metal dissolution was noted even after 75 days exposure to sodium chloride solution.

Modelling the influences of solid-state interdiffusion and dissolution on transient liquid phase sintering kinetics in a binary isomorphous system

A simple model was developed to predict the impact that solid-state interdiffusion and dissolution have on liquid formation and its duration during transient liquid phase sintering (TLPS). The model predicts that solid-state interdiffusion can dramatically reduce the amount of liquid initially formed during heating. This reduction is dependent on the heating rate and initial base metal particle size. In cases of sintering above the additive phase melting point, the model predicts that base metal dissolution increases liquid phase formation and that this additional melting reduces the base metal particle size. The model predicts that longer times are required to solidify isothermally the greater amounts of liquid formed at higher temperatures (because of dissolution). This agreed qualitatively with experimental results for a Ni-65 wt pct Cu TLPS mixture sintered at 1090 °C and 1140 °C. Quantitative comparisons between the model and experiment were good at 1140 °C; however, the rate of isothermal solidification was underestimated by the model for intermediate sintering times at 1085 °C.

A green technology for recovery of gold from non-metallic secondary sources

A process for the recovery of gold from processed gold-plated printed circuit boards, gold-coated bangles and gold-coated mirrors is described. It is based on heating the scrap material along with an “eco-friendly” or “green” reagent, 20% (v / v) formic acid solution to boiling temperature to separate the inorganic component from epoxy resin in gold-coated mirrors. Dissolution of base metals is affected using a strong oxidizing agent, 20%(w / v) potassium persulphate, which is also “eco-friendly” or “green”; and heating to boiling temperature. Recovery of gold is achieved by melting. The recovery efficiency is on par with the cyanidation process. The process can be scaled up and adopted by all categories of industries.

TLP Bonding of DS Ni Base Superalloy, GTD-111 Using Mixed Powder of Base Metal and Filler Metal

The effect of a mixed powder on the wide gap transient liquid phase diffusion bonding of a directionally solidified Ni base superalloy, GTD-111 was investigated. The mixed powder consisted of a mixture of a powdered Ni base filler (GNi-3) and powdered base metal (GTD-111). The range of the base metal powder was 40 to 70wt%. Bonding was performed at a temperature of 1463K, using various holding time. In the case of a lower 50wt%, the base metal powders completely melted and base metal mating at the interface dissolved at an early time, and extent of dissolution of base metal decreased with increasing mixing ratio. Liquid was eliminated by isothermal solidification, which was controlled by the diffusion of B into the base metal. The solids in the bonded interlayer grew epitaxially from the mating base metal inward from the insert metal and the number of grain boundaries formed at the bonded interlayer corresponded with those of the base metal. The finishing time for isothermal solidification was about 74ks. In the case 60wt% and higher, the base metal powders partially melted and remained in the vicinity of bonded interlayer. The solid was formed from the remaining powder and base metal mating at the interface. Finally, the bonded interlayer underwent the poly-crystallization when isothermal solidification was complete. The contents of Al and Ti in the bonded interlayer with a holding of 74ks were equal to that of the base metal.

等温凝固による結晶制御肉盛補修に関する基礎的検討

The applicability of built-up repairing by isothermal solidification to Ni-base single crystal superalloy CMSX-4 was investigated using Ni-Cr-B filler metals. Base metal dissolution and isothermal solidification behaviors were examined under various heat treatment conditions. Microstructure of the repaired region could be classified into eutectic zone, normally solidified zone, isothermally solidified zone, precipitated zone in the base metal and substrate. Isothermally solidified zone and precipitated zone in the base metal were found to possess the identical crystal orientation with the base metal one. The dissolution width of base metal and the isothermal solidification width increased with repairing temperature and holding time. The single-crystallization could be achieved in the isothermally solidified zone of the repaired region. The built-up repairing up to 38μm in width could be made at the repairing condition of 1448K×176.4ks by using a Ni-Cr-B filler metal.

Electrochemical behavior of multicomponent amorphous and nanocrystalline Zr-based alloys in different environments

Electrochemical behavior of multicomponent melt spun Zr-based amorphous as well as nanocrystalline alloys have been studied in three different corrosive media (neutral NaCl, basic NaOH and acidic H 2SO 4 solutions). Due to the presence of strong passivating elements, (Zr and Ti) melt spun ternary alloys (Zr 55Ti 25Ni 20) have shown complete passivation in NaCl solution even as they contain a small amount of crystallinity. Amorphous multicomponent alloys containing Cu (Zr 58Cu 28Al 10Ti 4 and Zr 65Cu 7.5Al 7.5Ni 10Pd 10) show active nature in NaCl solution and this is strongly related to selective dissolution of base metal (Zr) and enrichment of Cu in the pit region. In NaOH and H 2SO 4 solutions, all the alloys have shown complete passivation irrespective of the alloy composition.

Dissolution behaviour of Ti/Cu contact reaction

This paper investigates the base metal dissolution behaviour of Ti/Cu contact reaction couples at temperatures of 880–940°C and holding times of 1–180 s. The results show that once the temperature reached the eutectic point of Ti and Cu (875°C), the liquid formed quickly. For Ti/Cu contact reaction couples, the formation of eutectic liquid phase had a direction affected by the contact assembly, i.e. the eutectic liquid phase formed first at the Cu side, and then spread along the depth direction of Cu. The width of the eutectic liquid zone when Ti was placed on Cu was wider than when Ti was placed under Cu. Also, the shape of the upper liquid zone was wave-like while the shape of the lower liquid zone was planar, the formation mechanisms of the two liquid zone are related to the spreading behaviour of the eutectic liquid at the Ti/Cu interface. The formation process of Ti/Cu eutectic liquid zone was similar to that of the traditional solid-state diffusion zone, and the relationship between the width of the liquid zone and holding time obeyed a square root law.

The effect of processing variables on the microstructures and properties of aluminum brazed joints

Aluminum brazed joints are used extensively in the automotive and aircraft industries. In order to insure the integrity of the bond, the effects of processing variables on the quality of the bond must be understood. The effects of brazing period and joint thickness on the microstructure, tensile properties, microhardness and micromechanisms of failure of two aluminum alloy 3003 plates connected by a layer of 4047 aluminum filler material were investigated. It was found that the amount of aluminum-silicon eutectic microstructure in the reaction zone decreased with increasing brazing period and decreasing joint thickness. This was attributed to silicon diffusion from the joint material and dissolution of base metal and its entrance into the liquid joint. The amount of shrinkage porosity in the reaction zone was found to increase with increasing brazing period due to base material solutioning. The ultimate tensile strength of joints decreased with increasing brazing period and decreasing joint thickness. This was attributed to the joint microstructure and shrinkage porosity formed in the joint. Shrinkage porosity was found to be the primary cause of decreased joint strength. Joints with 10 minutes brazing period failed within the base material, while for brazing periods greater than 10 minutes, joints failed within the aluminum-silicon eutectic microstructure of the reaction zone. This indicated that the joint strength was greater than the base material for joint with brazing period of 10 minutes. Finite element analysis was performed to determine the effect of joint material yield strength and joint thickness on the stress and strain field in the brazed joint. Finite element analysis results supported experimental observations.

Isothermal Solidification Behavior During the Transient Liquid Phase Bonding Process of Nickel Using Binary Filler Metals

Transient liquid phase (TLP) bonding process of Ni using Ni–11.0 mass%P binary filler metal was simulated by using a mathematical model based on diffusion analysis. In the model, diffusion-controlled transformation was assumed, and the base metal dissolution in the early stage and the subsequent isothermal solidification stage of the TLP bonding process were simulated. The calculated width of the eutectic structure at the bonding region agreed well with the experimental result and showed the validity of the model. In order to obtain the condition to reduce isothermal solidification time, the effect of factors, such as the width of filler metal, diffusivity of solute element in Ni and partition coefficient of element, were investigated by numerical simulation. The simulation showed that isothermal solidification time remarkably decreases with increasing partition coefficient of solute element. In order to confirm the numerical prediction, the TLP bonding experiment of Ni using Cu filler metal was carried out (the partition coefficient of Cu in Ni is close to unity). The experimental result showed that Cu filler metal remarkably shortened the isothermal solidification time and showed the validity of the prediction.