New approaches for brazing temperature sensitive materials

PVD deposited copper interlayers as filler materials were used in order to manufacture TLP brazed magnesium joints. The microstructure and interface characteristics of the overlap joints were investigated by optical microscopy, scanning electron microscope with energy dispersive spectrometer and tensile testing. Sound brazed joints could be achieved. The dwell time is the main factor to control the thickness of the reaction layer. It was shown that the deposited copper filler metal clearly reacted with the magnesium substrate , resulting in the formation of a magnesium solid solution （Mg） with different amount of copper, aluminum and zinc as well as Mg2Cu phases. With the progressing diffusion, the formation of intermetaUic compounds was suppressed and the hardness distribution in the brazing seam homogenized. The joints fractured at the interface, and the maximum average tensile shear strength of overlap joints reached 85 MPa.     

Distribution behavior of Copper and Tin between FeO-rich slag and iron solution

The distribution behavior of residual elements copper and tin between FeO-rich slag and iron solution was investigated under the condition of an induction furnace. The results indicate that a part of copper and tin is incidently oxidized when oxygen is blasted into bath to react with iron element. The distribution ratio of copper and tin between slag and metal is about 0.1. Phenomena of Cu and Sn elements segregation and accumulation in slag were observed by means of EPMA analysis. The distribution ratio of copper and tin between slag and metal may descend with increasing of CaO content in slag.     

A coupled model on fluid flow,heat transfer and solidification in continuous casting mold

Fluid flow, heat transfer and solidification of steel in the mold are so complex but crucial, determining the surface quality of the continuous casting slab. In the current study, a 2D numerical model was established by Fluent software to simulate the fluid flow, heat transfer and solidification of the steel in the mold. The VOF model and k-ε model were applied to simulate the flow field of the three phases(steel, slag and air), and solidification model was used to simulate the solidification process. The phenomena at the meniscus were also explored through interfacial tension between the liquid steel and slag as well as the mold oscillation. The model included a 20 mm thick mold to clarify the heat transfer and the temperature distribution of the mold. The simulation results show that the liquid steel flows as upper backflow and lower backflow in the mold, and that a small circulation forms at the meniscus. The liquid slag flows away from the corner at the meniscus or infiltrates into the gap between the mold and the shell with the mold oscillating at the negative strip stage or at the positive strip stage. The simulated pitch and the depth of oscillation marks approximate to the theoretical pitch and measured depth on the slab.     

Development of copper coatings on molybdenum powders by electroless plating technique

Mo powders with average particle size of 3 μm were attempted to coat with copper by electroless plating technique. The effect of the solution composition and plating conditions on the electroless copper plating was studied. The uncoated and coated powders were subjected to the microstructural studies by SEM and the phases were analyzed by XRD. The results indicate that the Mo powders are coated with copper, at （he same time, Mo-Cu composite powders with Cu content ranging from 15% to 85% （mass fraction） can be obtained. The optimal values of pH, HCHO concentration and temperature are in the ranges of 12-13, 22-26 ml/L and 60-65℃, respectively. The diffusion-shrinkage autocatalytic model is suggested for the growth mechanism of electroless coating over the surface.     

MECHANISM AND KINETICS OF TRANSFORMATION OF ALUMINA INCLUSIONS BY CALCIUM TREATMENT

The basic mechanism and kinetics of the transformation process of alumina inclusions in steel was reported when calcium introduced into the steel by wire feeding orpowder injection. To clarify the mechanisms model, experiments were performed by studying reactions between AltOs and CaO in a laboratory furnace and by performing calcium treatments in an 8kg induction furnace for Al deoxidised melt. The phases formed during the reaction between Al2O3 and CaO were examined by SEM-EDS （scanning electron microscope-energy dispersive spectrometer）, and the reaction sequence of Al2O3=〉 CA6=〉 CA2 =〉 CA =〉 CAx（l） was discussed in term of the experimental observations. The kinetics of the reaction of calcium with alumina inclusions were simulated by immersing alumina plates in a Ca treated steel melt in the induction furnace. Results were compared with observations of real inclusion transformation. A kinetic model was proposed based on the results.     

Copper base materials prepared by gel-casting process

Gel-casting process was developed as a new molding process in the field of copper base powder metallurgy to manufacture metal parts with excellent performance and complex shapes.Through changing the parameters of gel-casting process,such as dispersant and solid loading,the corresponding effects on the rheology of Cu slurries,molding and sintering behaviors were studied.The results show that the viscosity of Cu slurries was significantly reduced with an increase in dispersant.The most appropriate solid loading was found to be 61% and the sintering temperature was 910℃ in these experiments.After the optimization of parameters of gel-casting process,copper composite parts with relatively high density and better properties were obtained.     

Solid-State Diffusion Bonding of Nb_(SS)/Nb_5Si_3 Composite Using Ni/Al and Ti/Al Nanolayers

Diffusion bonding of refractory Nb–Si-based alloy was performed with Ni/Al and Ti/Al nanolayers under the condition of 1473 K/30 MPa/60 min. The Nb_(SS)/Nb_5Si_3 in situ composite with the nominal composition of Nb–22 Ti–16 Si–3 Cr–3 Al–2 Hf was used as the parent material. The joint microstructures were examined by using a scanning electron microscope equipped with an X-ray energy dispersive spectrometer. Shear test was conducted for the bonded joints at room temperature.Within the joint bonded with Ni/Al multilayer, element diffusion occurred between the base metal and the nanolayer, with the reaction products of AlNb_2 + Ni_3 Al, NiAl and AlNi_2 Ti phases. The average shear strength was 182 MPa. While using Ti/Al multilayer, the interface mainly consisted of TiAl,(Ti,Nb)Al and(Ti,Nb)_2 Al phases, and the corresponding joints exhibited an increased strength of 228 MPa. In this case, the fracture mainly took place in the TiAl phase and presented a typical brittle characteristic.     

Study of ultrahigh-purity copper billets refined by vacuum melting and directional solidification

The purpose of this paper is to study large-sized copper billets refined with 5N ultrahigh purity after vacuum melting and directional solidifi-cation (VMDS). The precise impurity analysis of copper billets was carried out with a glow discharge mass spectrometer (GDMS). The re-sults demonstrate that the total concentration of twenty-two impurities is decreased by 63.1wt.%-66.5 wt.%. Ag, P, S, Na, Mg, Se, Zn, In and Bi are easy to be removed due to lgPimp - lgPCu > 1.5, and they can be removed effectively under the vacuum condition of 1650-1700 K for 30 min. The electrical conductivity of 5N copper is higher than that of the raw material as the impurity concentrations decrease. The segrega-tion effect in directional solidification can be remarkable when the equilibrium distribution coefficient (k0) value is less than 0.65 due to the strong affinity of Cu for some metallic and non-metallic impurities.     

Cleaning of high antimony smelting slag from an oxygen-enriched bottom-blown by direct reduction

Cleaning of high antimony smelting slag from an oxygen-enriched bottom-blown was tested by direct reduction in a laboratory-scale electric furnace.The effects of added CaO,mass ratio of coal(experimental)to coal(theoretical)(ω)and the slag type on the reduction procedure were considered.The contents of Sb and Au were investigated.Iron contamination of the metal phase was analyzed as this may impede the economical viability of this process.The initial slag,coal and CaO were mixed and homogenized before charging into the furnace,and the residual slag averagely contains 1.26 g.ton-1 Au and1.17 wt% Sb.However,the iron contamination of antimony alloy becomes unacceptably high in this case as the metal phases contain up to 10 wt% Fe.In the slag system with mass ratio of SiO_2:FeO:CaO= 45:27:18,the residual slag obtained after reduction under these conditions averagely contains1 g·ton~(-1) Au and1 wt% Sb,and the metal phase contains7 wt% Fe.The recoveries of Au in the metal phase are98 % in all experiments which is proved to be an economic and cleaning process.     

Strength of deformation-processed Cu-Fe in-situ composites

The strength of the deformation-processed Cu-Fe in-situ composite was conducted by material test system(MTS). The results show that the strength increases with the increasing deformation strain and iron content,which is greater than that of the calculated value based on the rule of mixture. The mechanism of strengthening was analysed and evidenced by interface barrier. The correlation between the strength and the thickness of copper phase (tCu) obeys Hall-Petch relationship and can be described well by geometrical necessary dislocation model and interface as dislocation source model.     

Recovery of valuable metals from spent lithium ion batteries by smelting reduction process based on FeO–SiO2–Al2O3 slag system

A novel smelting reduction process based on FeO–SiO₂–Al₂O₃ slag system for spent lithium ion batteries with Al cans was developed, while using copper slag as the only slag former. The feasibility of the process and the mechanism of copper loss in slag were investigated. 98.83% Co, 98.39% Ni and 93.57% Cu were recovered under the optimum conditions of slag former/battery mass ratio of 4.0:1, smelting temperature of 1723 K, and smelting mass ratio of time of 30 min. The FeO–SiO₂–Al₂O₃ slag system for the smelting process is appropriate under the conditions of m(FeO):m(SiO₂)=0.58:1–1.03:1, and 17.19%–21.52% Al₂O₃ content. The obtained alloy was mainly composed of Fe–Co–Cu–Ni solid solution including small amounts of matte. The obtained slag mainly consisted of fayalite and hercynite. Meanwhile, the mechanism of copper loss is the mechanical entrainment from strip-like fayalite particles in the main form of copper sulfide and metallic copper.     

含钴铜转炉渣的工艺矿物学

研究了铜转炉渣的化学与矿物学特征,用光学显微镜查明了炉渣各主要渣相为铁橄榄石,磁铁矿和无定形玻璃体,铜主要以冰铜相裹夹于渣相中,铜滴的尺度与渣的冷却历史有关。用X射线衍射谱,扫描电子显微镜,X射线能谱和X射线波谱及化学物相分析,对铜和钴的赋存状态及在各相中的分布进行了表征和量化。结果表明,钴主要以类质同象形式取代铁橄榄石和磁铁矿晶格中部分Fe^2 ,作为氧化物富集其中,二者约占钴总量的95％,渣中钴的提取需要以铁橄榄石和磁铁矿的分解为前提,使钴的氧化的游离出来而酸溶。     

铜闪速熔炼渣中砷的赋存状态和浸出毒性（英文）

铜冶炼含砷炉渣的高效安全处置取决于对其含砷物相及其浸出毒性的准确认识。采用X射线荧光光谱、X射线衍射、电子探针显微分析、扫描电子显微术和选择性逐级提取法对铜熔炼渣中的含砷物相进行鉴定,并基于对炉渣中不同含砷物相的选择性逐级提取结果探讨渣中砷浸出毒性的可能来源。结果表明,砷以水溶性砷、铜砷金属间化合物、铜砷硫化物以及固化在铁橄榄石和硅酸盐玻璃相中的砷等形式赋存在熔炼渣中。浮选过程可以去除熔炼渣中的水溶性砷并回收铜砷金属间化合物,降低渣尾矿的砷浸出毒性,使其符合USEPA和SEPA标准要求。     

Interaction mechanism between arsenate and fayalite-type copper slag at high temperatures

The interaction mechanism between sodium arsenate and fayalite-type copper slag at 1200 °C was investigated through XRD, XPS, HRTEM, TCLP and other technical means and methods. The results indicated that the proportions of sodium arsenate in the slag and flue gas phases were approximately 30% and 70%, respectively. The addition of sodium arsenate depolymerized the fayalite structure and changed it from a crystalline state to an amorphous state. The fayalite structural changes indicated that the [AsO₄] tetrahedron in sodium arsenate combined with the [SiO₄] tetrahedron and [FeO₄] tetrahedron through bridging oxygen to form a silicate glass structure. The TCLP test results of the samples before and after the high temperature reaction of fayalite and sodium arsenate showed that after high temperature reaction, fayalite could effectively reduce the leaching toxicity of sodium arsenate, reducing the leaching concentration of arsenic from 3025.52 to 12.8 mg /L before and after reaction, respectively.     

Solid-State Phase Equilibria of the Cu-S System: Thermodynamic Modeling

All phase equilibria and thermodynamic data available in the literature on the copper sulfides high- and low-temperature chalcocite, djurleite and anilite have been critically analyzed for optimization of the solid-state phase diagram of the Cu-S system at 1 bar total pressure. A two-sublattice approach derived from a recently developed Gibbs energy model for digenite enables the consideration of the solid solution nature of both modifications of chalcocite and for the first time of djurleite. Anilite is considered as stoichiometric compound. The sulfur solubility of metallic copper is described by a substitutional approach. The obtained Gibbs energy functions for high- and low-temperature chalcocite, djurleite, anilite and copper alloy phase allow computations and predictions of phase equilibria and thermodynamic properties in good accordance with experimental data of the Cu-S solid-state system.     

Effect of Fe/SiO2 and CaO/SiO2 mass ratios on metal recovery rate and metal content in slag in oxygen-enriched direct smelting of jamesonite concentrate

The oxygen-enriched direct smelting of jamesonite concentrate was carried out at 1250 °C by changing the slag composition. The effects of Fe/SiO₂ and CaO/SiO₂ mass ratios on the metal recovery rate as well as metal content in slag were investigated. Experimental results indicated that the metal (Pb+Sb) recovery rate was up to 88.30%, and metal (Pb+Sb) content in slag was below 1 wt.% under the condition of slag composition of 21−22 wt.% Fe, 19−20 wt.% SiO₂ and 17−18 wt.% CaO with Fe/SiO₂ mass ratio of 1.1:1 and CaO/SiO₂ mass ratio of 0.9:1. The microanalysis of the alloy and slag demonstrated that the main phases in the alloy contained metallic Pb, metallic Sb and a small amount of Cu₂Sb and FeSb₂ intermetallic compounds. The slag was mainly composed of kirschsteinite and fayalite. Zinc in the raw material was mainly oxidized into the slag phase in the form of zinc oxide.     

Thermodynamic Assessment of Slag–Matte–Metal Equilibria in the Cu-Fe-O-S-Si System

Equilibria among the slag, matte and metal phases in the Cu-Fe-O-S-Si system are critically assessed using thermodynamic modeling. The relationships among matte grade, temperature, partial pressure of SO₂, Fe/SiO₂ in the slag, and the copper concentration in the slag are described by the model, as well as the concentrations of other elements in all phases. A thermodynamic database is created, which can be used for understanding and improving the pyrometallurgical production of copper. An extensive experimental dataset includes the most recent results obtained by the equilibration/quenching/EPMA analysis technique. These data allow to distinguish the physical entrainment of the matte and solid phases in the slag from chemical solubility. As a result, it is possible to describe the copper solubility in the slag with high accuracy and establish the relationship between copper and sulfur in the slag. The thermodynamic database of the present study is consistent with previously reported thermodynamic evaluations of binary, ternary and quaternary subsystems. The slag phase is modeled using the two-sublattice modified quasichemical model in the quadruplet approximation. The matte and metal liquid phases are modeled as one solution using the single-sublattice modified quasichemical model in the pair approximation.     

Minimization of Copper Losses in Copper Smelting Slag During Electric Furnace Treatment

In the quest to achieve the highest metal recovery during the smelting of copper concentrates, this study has evaluated the minimum level of soluble copper in iron-silicate slags. The experimental work was performed under slag-cleaning conditions for different levels of Fe in the matte and for a range of Fe/SiO₂ ratios in the slag. All experiments were carried out under conditions where three phases were present (copper?Cmatte?Cslag), which is the condition typically prevailing in many slag-cleaning electric furnaces. The %Fe in the electric furnace matte was varied between 0.5?wt.% and 11?wt.%, and two different Fe/SiO₂ ratios in the slag were used (targeted values were 1.4 and 1.6). All experiments were performed at 1200°C. From thermodynamic considerations, from industrial experience, and from the results obtained in this study, the minimum soluble copper content in the electric furnace slag is expected to be near 0.55?wt.% Cu. This level does not account for a portion of the copper present as mechanically entrained matte/metal droplets. Taking this into account, the current authors believe an overall copper level in discard slag between 0.7?wt.% and 0.8?wt.% can be obtained with optimal operating conditions. For these conditions, the copper losses in the slag are roughly 75% as dissolved copper and 25% as entrained matte and copper. Such conditions include operating the electric furnace at metallic copper saturation, maintaining the %Fe in the electric furnace matte between 6?wt.% and 9?wt.%, not exceeding a slag temperature of 1250°C, and controlling the Fe/SiO₂ ratio in the smelting furnace slag at ??1.5. In addition, magnetite reduction needs to be performed efficiently during the slag-cleaning cycle so as to maintain a total magnetite content of ??7?wt.% in the discard slag. The authors further consider that under exceptionally well-controlled conditions, a copper content in electric furnace discard slag between 0.55?wt.% and 0.7?wt.% can be obtained, by minimizing entrained matte and copper solubility in the discard slag.     

The behavior of sulfur in industrial pyrometallurgical slags

Dissolution of sulfur in industrial slags, even at such a low level as 1 mass% S or so, increases the solubility of certain valuable metals by an order of magnitude. The phenomenon is accounted for in terms of Flood-Førland-Grjotheim’s model for dianionic salt solutions, whereas its rigorous analysis requires the digaseous Gibbs-Duhem integration. In the research described here, the distribution of sulfur among gas, slag, and metallic iron phases in the bath smelting of iron ore was computer-simulated based on a two-sites model coupled with sulfide capacity data. The solubilities of Ag, Cu, Co, and Ni in industrial slags are reviewed by applying the sulfidic-oxidic dissolution model to copper-matte smelting, nickel-slag cleaning (Falconbridge, Canada), and the imperial smelting process for zinc and lead (Hachinohe, Japan).     

激光熔覆Ni-Ti-Si合金组织及微观力学性能研究

采用激光熔覆技术在铜表面制备了55Ni-35Ti-10Si (at.%)合金熔覆层,熔覆层呈现上、下两层。利用光学显微镜(OM)、扫描电子显微镜(SEM)、X 射线衍射仪(XRD)、能谱仪(EDS)分析上层组织为树枝晶,组成相为初生钛固溶体+枝晶间Ni₃Si;下层组织为胞状晶,组成相为初生钛固溶体+枝晶间铜固溶体,胞状晶区高度约为200μm。利用KGT和LKT改进模型计算得出熔覆层熔池凝固过程枝晶尖端过冷度-凝固速度曲线,从热力学角度分析熔覆层出现分层的机理。对熔覆层进行显微硬度试验,得到上层树枝晶区域和下层胞状晶区域平均硬度分别为800HV和220HV。提出下层胞状晶区域的存在有利于熔覆层与基体间性能过渡,提高了熔覆层稳定性。