Oxidation of copper ultrafine powders and nanopowders produced by vapor phase condensation

The oxidation of copper nanopowders fabricated by metal evaporation and condensation is studied. It is found that, in contrast to the oxidation of bulk copper samples, the oxidation of nanopowders can provide the formation of a CuO surface layer on copper particles in a reactor, bypassing the stage of Cu₂O formation. The Cu₂O oxide that forms on the surface of unoxidized copper powder particles spontaneously transforms almost completely into a more thermodynamically stable phase (CuO oxide) during storage in air under natural conditions.     

Experimental Liquidus Studies of the Pb-Cu-Si-O System in Equilibrium with Metallic Pb-Cu Alloys

Phase equilibria of the Pb-Cu-Si-O system have been investigated in the temperature range from 1073 K to 1673 K (800 °C to 1400 °C) for oxide liquid (slag) in equilibrium with solid Cu metal and/or liquid Pb-Cu alloy, and solid oxide phases: (a) quartz or tridymite (SiO₂) and (b) cuprite (Cu₂O). High-temperature equilibration on silica or copper substrates was performed, followed by quenching, and direct measurement of Pb, Cu, and Si concentrations in the liquid and solid phases using the electron probe X-ray microanalysis has been employed to accurately characterize the system in equilibrium with Cu or Pb-Cu metal. All results are projected onto the PbO-“CuO_0.5”-SiO₂ plane for presentation purposes. The present study is the first-ever systematic investigation of this system to describe the slag liquidus temperatures in the silica and cuprite primary phase fields.     

国外某铜矿选冶试验研究

国外某铜矿中铜含量为6．91％,且主要以氧化铜的形式存在,氧化率高达98．30％,结合率达45．60％,属高结合率的氧化铜矿。采用浮选和重选工艺难以有效回收。通过采用搅拌浸出一萃取一电积工艺可以获得较好的选冶指标。     

Kinetic study of the dissolution of cuprite in oxyacid solutions

The rates of disproportionation dissolution of three artificial cuprite samples were measured in sulfuric acid and perchloric acid solutions, from which oxygen had been stripped, at different concentrations and temperatures. Samples were prepared by electrolysis, sintering of electro-lytically produced cuprite, and oxidation of hot-rolled copper sheets. The effects of sodium sulfate and sodium perchlorate on the dissolution of cuprite were also examined. Metal copper formed by the disproportionation reaction plays a role as a barrier for further dissolution of cuprite. Apparent activation energies were determined in the temperature range of 293 to 323 K for the initial stage of the disproportionation reaction of cuprites. The values ranged from 14.7 to 24.9 kJ mol^-1 in 0.003 mol dm^-3 sulfuric acid and perchloric acid and from 29.7 to 52.0 kJ mol^-1 in 0.1 mol dm^-3 sulfuric acid and perchloric acid. Judging from the effects of temper-ature, agitation speed, acid concentration, and common salt additions, it is concluded that the adsorption of H⁺ onto the surface site is important in determining the dissolution rate of cuprite in oxyacid solutions. The dissolution behaviors of different cuprite samples were also morpho-logically examined.     

Investigating the surface of particles of ultradispersed copper powders obtained by gas-phase condensation

Ultradispersed powders of metal copper obtained by evaporation-condensation technology are investigated. It is shown that, depending on the evaporation rate, various dispersities and degrees of agglomeration of copper powders are attained with the conservation of the weight fraction of copper in them no lower than 99.0%. It is established using the XPES method that a 5- to 6-nm-thick CuO layer (on the surface of which there is a Cu₂O layer up to 1 nm thick) is always present on the surface of Cu particles of all powders under consideration. It is assumed that, because of a low residual air pressure in industrial installations, the surface layer of copper oxidizes to the lower oxide Cu₂O during the evaporation of metal, while oxide CuO is formed as a result of the decomposition of Cu₂O during the condensation of copper particles. The smaller the particle size of the powder is, the higher the content of oxides is.     

A mineralogical study of the deportment and reaction of silver during copper electrorefining

The majority (>95 pct) of the silver in copper anodes occurs in metastable solid solution in the copper matrix; only a small percentage is present in solid solution in Cu₂(Se,Te) inclusions, as a constituent of complex Cu-Pb-As-Sb-Bi oxides or as tiny grains of Ag-Cu alloy. During elec-trorefining, the silver in the copper matrix dissolves, but it is rapidly removed from the elec-trolyte by a variety of reactions. Part of the silver is precipitated in elemental form by cuprous ion, but some of this metallic silver subsequently redissolves. Some of the dissolved silver precipitates as a complex Cu-Ag-Pb-As-Se oxidate phase which agglomerates the particles in the anode slimes, and some reacts with the Cu₂(Se,Te) inclusions liberated from the anode to form, sequentially, silver-bearing copper selenide, AgCuSe, copper-bearing silver selenide, and Ag₂Se. Several selenide species are present in the anode slimes, and individual selenide particles com-monly consist of more than one selenide species. Because of the diversity and complexity of the silver-bearing phases present, the Ag/Se ratio in the anode is only an approximate indicator of the selenide species present in the anode slimes.     

Influence of Nb and Cu Elements on the Intermetallic Particles Morphology in Ti/Al Multilayer Composite Processed Through Hot Pressing and Rolling

Ti–Al–Nb composites were produced by solid state diffusion bonding through hot pressing and rolling followed by annealing at 700 °C for 0.5, 1, 1.5 and 2 h. The morphologies of TiAl₃ intermetallics were investigated by Scanning Electron Microscopy combined with Energy-dispersive X-ray spectroscopy. Titanium tri-aluminide (TiAl₃) particles with blocky morphology were dispersed into Aluminum matrix. In the presence of niobium and copper, TiAl₃ particles were produced in different sizes and morphologies. The presence of Nb in the composite led to the formation of irregular angular morphology, while the copper resulted in cubic morphology of the intermetallic particles. The EDS results indicated that TiAl₃, (Ti, Nb)Al₃ and (Ti, Nb, Cu)Al₃ intermetallic compounds appeared near Ti zone, Nb Zone and in the presence of Cu, respectively.     

RELEASE OF STORED ENERGY IN OXIDE-DISPERSION-STRENGTHENED COPPER

Abstract

The pattern of energy release on annealing was followed by calorimetric means for a series of oxide-dispersion-strengthened copper alloys extruded at high reduction ratio. Included among the test materials were two Cu-Al₂O₃ alloys prepared by salt decpmposition, several Cu-SiO₂ and Cu-Al₂O₃ alloys prepared by internal oxidation, and a CU-CU₂O alloy prepared by surface oxidation. For several of the alloys energy releases were observed that confirm the expected high levels of energy stored during high strain rate extrusion. Values of 0·41 and 0·42 cal/g were measured and correspond to levels of cold work found in copper severely deformed in torsion. The energy release was observed at temperatures high above that normal for the recrystallization of cold-worked copper.     

Precursor Dependent Structural Phase Evolution in Hydrothermally Prepared Cu<Subscript>2</Subscript>O Octahedrons and Cu Micro-Flakes and Their Structural and Optical Properties

Cuprous oxide (Cu₂O) and metallic copper particles with different microstructures have been prepared by a single-step hydrothermal method by using copper acetate monohydrate and sodium hydroxide as precursors, d-glucose as reducing agent, and poly (vinylpyrrolidone) as stabilizing agent. It was found that the concentration of the NaOH in the reactant solution played a significant role in the structural phase formation of the product. Further, it was also optimized to get either the single phase of Cu₂O or Cu or the mixed phase of Cu₂O and Cu depending on the NaOH content in the reaction mixture. The product material was systematically investigated by x-ray diffraction (XRD), Rietveld refinement, UV–Vis, Raman spectroscopies, scanning electron microscopy (SEM), and X-ray energy dispersive spectroscopy (XEDS). A thorough analysis of the XRD patterns in a standard method as well as by Rietveld refinement have shown the cubic phases for both Cu₂O and Cu. The same phases have been retained in the mixed phase sample also. Optical band gap was determined through Tauc plot to be 1.95 eV. Microstructural studies by SEM showed that the Cu particles were formed as micro flakes whereas the Cu₂O particles were formed with the well-defined octahedral morphology. The XEDS analysis confirmed the chemical composition in Cu₂O. This work reports the dependence of NaOH concentration in the reactant solution on the type of product (single phase or a mixed phases of Cu₂O and Cu) and their structural and optical properties.     

Internal oxidation of CuFe—I. Small angle x-ray scattering study of oxide precipitation

The combination of 3D-small-angle X-ray scattering, anomalous small-angle X-ray scattering and X-ray diffraction was used to characterize the nature and morphology of iron-oxide precipitates formed by internal oxidation of CuFe single crystals. Two types of iron-oxides with spinel structure were identified. The first type, Fe₃O₄ (90% of the total amount of precipitates), forms plates on {111}-planes of the copper lattice, whereas the other, with a composition close to γ-Fe₂O₃, forms plates on {100}-planes. The occurrence of plate-like precipitates on well defined habit planes is attributed to the large elastic misfit between matrix and precipitates. The fact that two oxides with very similar structure grow on different habit planes is interpreted as a bifurcation between two possible orientation relations during nucleation of the oxide.     

Processing,microstructure, and mechanical properties of cast <Emphasis Type="Italic">in-Situ</Emphasis> Al(Mg,Mn)-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>(MnO<Subscript>2</Subscript>) composite

Cast particulate composites, containing in-situ generated reinforcing particles of alumina, have been developed by solidification of slurry obtained by dispersion of externally added manganese dioxide particles (MnO₂) in molten aluminum, and alumina is formed by reaction of manganese dioxide with molten aluminum. The chemical reaction also releases manganese into molten aluminum. Magnesium is added to the melt in order to help wetting of alumina particles by molten aluminum and to retain the particles inside the melt. The present work aims to understand the influence of key parameters such as processing temperature, time, and the amount of MnO₂ particles added on the microstructure and mechanical properties of the resulting cast in-situ composites. The sequence of addition of MnO₂ particles and magnesium has significant influence on the microstructure and mechanical properties. Increasing processing temperature and time increases the extent of reduction of MnO₂ particles, generating more alumina particles as well as releasing more manganese to the matrix alloy. Alumina helps to nucleate finer and sometimes blocky MnAl₆ in the matrix of the composite and thereby results in relatively higher ductility and increased strength in the composite as compared to the base alloy of similar composition. Even in the presence of relatively higher porosity of 8 to 9 vol pct, one observes a percent elongation not below 7 to 8 pct, which is considerably higher than those observed in cast Al(Mg)-Al₂O₃ composite synthesized by externally added alumina particles.     

Internal oxidation of dilute Cu-Ti alloys

The kinetics of internal oxidation of dilute Cu-Ti solid solutions, containing up to 1 wt pct Ti have been investigated over the temperature range 700 to 900°C, and the oxide morphologies produced have been studied by electron metallography. Values of the solubility-diffusivity products for oxygen in copper (N_o ^(s)D_o) are in good agreement with those obtained for pure copper by electrochemical techniques. The TiO₂ particles formed in the Cu-matrix are extremely small (50-200?) and appear to be ellipsoidal in shape. The oxide particle size has been observed to increase linearly with distance below the specimen surface. In addition, electron metallography reveals TiO₂ particles both in the matrix and at grain boundaries which exhibit interesting fringe contrast or “stripes” which are perpendicular to the major axis of the ellipsoids. The origin and possible significance of these regions in terms of coherency of the TiO₂/Cu interfaces are discussed. The interfacial energies for incoherent TiO₂ /Cu interfaces have been found to be quite low, on the order of 400 to 700 ergs/cm². D. ADAMONIS is formerly Graduate Student Assistant     

Novel oxide-dispersion-strengthened copper alloys from rapidly solidified precursors: Part 1. Microstructural development

ZrO₂, Y₂O₃, and rare earth oxides with related structures are attractive candidates for dispersion strengthening of copper alloys but pose significant processing challenges owing to the low solubility of the oxide-forming elements in Cu. It is shown that the problems may be circumvented by a synthesis approach coupling rapid solidification and internal oxidation, followed by standard powder metallurgy consolidation. Cu-Zr and Cu-Y alloys were melt spun into ribbons ∼-50-to 150-Μm thick and internally oxidized at 1023 to 1223 K to yield ∼1 vol pct of ZrO₂ or Y₂O₃ particles ranging in size from 5 nm up to ∼3150 nm. The coarser oxides result from direct oxidation of the intermetallic segregate, whereas the finer ones are generated by a dissolution-reprecipitation process. The relative proportions of fine and coarse oxides and the homogeneity of the distribution are related to segregation scale in the melt-spun ribbon and the relative permeabilities of oxygen and the oxidizable element in the alloy, which depend on the internal oxidation temperature. The oxide dispersoids were mostly cubic zirconia or cubic yttria and exhibited predominantly cube-on-cube orientation relationships with the matrix. Analysis of particle shapes revealed that the dominant interfaces are of the type {001}_OX ∥ {001}_Cu and {1ˉ11}_OX ∥ {1ˉ11}_Cu and could be explained by image charge interaction concepts. Extrusion produced an elongated grain structure but no significant changes in the oxide distribution. MICHAEL S. NAGORKA, formerly Graduate Research Assistant, High Performance Composites Center, Materials Department, College of Engineering, University of California at Santa Barbara     

A structural study of oxidation in a zirconia-toughened alumina fiber-reinforced NiAl composite

A composite of NiAl reinforced with continuous zirconia-toughened alumina (PRD-166) fibers was fabricated by pressure casting. The chemical stability of the composite at 1100 °C in vacuum and air was investigated by optical and transmission electron microscopy and energy-dispersive spectroscopy (EDS). Exposure of the fiber to the molten metal caused ZrO₂ particles in the fiber to move to the surface, thus permitting dissolution of ZrO₂ into the molten metal. The dissolved Zr reacted with A1₂O₃ of the fiber and formed ZrO₂ particles in some regions at the fiber/matrix interface. Vacuum annealing did not result in any noticeable change in the microstructure. Air annealing led to the precipitation of ZrO₂ within the matrix near the fiber/matrix interface. A thin layer of A1₂O₃ was observed to envelop the ZrO₂ particles and cover the fiber. During air annealing, Al oxidized preferentially, thereby continually reducing the Al content of the β-NiAl. This caused a progressive change in the microstructure of the matrix from β-NiAl to premartensitic microstructure, to martensitic structure, followed by nucleation and growth of Ni₃Al, to the development of a two-phase microstructure consisting of Ni₃Al cuboids dispersed in a disordered α-Ni(Al) and, subsequently, the formation of single-phase α-Ni(Al). The orientation relationship between Ni₃Al and NiAl was . Internal oxidation of α-Ni(Al) led to precipitation of A1₂O₃ particles which subsequently reacted with Ni, in the presence of O, to form NiO · A1₂O₃ spinel. The Ni was oxidized to formβ-NiO. Titanium-containing, platelike precipitates with a {111} habit plane were occasionally observed in NiO. Some larger NiTiO₃ particles were also formed within NiO. Diffusion of O through the interphase and grain boundaries of the fiber is believed to be responsible for the rapid oxidation of the composite.     

The precipitation behavior of a Zr-2.5 wt pct Nb alloy

The morphology, crystallography, and nature of precipitates in a quenched and aged Zr-2.5 wt pct Nb alloy has been studied by transmission electron microscopy. The needle-shaped matrix precipitates and equiaxed twin boundary nucleated precipitates produced by aging at 500 °C were the equilibrium Nb-rich β₂ phase. On aging at 600 °C, the matrix precipitation was a mixture of β₂ needles and coarse metastable Zr-rich β₁ particles, while only β₁ particles were found at twin boundaries. The growth direction of the needle-shaped particles, 6.6 deg to 8.2 deg from (1-100)_h, and their orientation relationship can be predicted by an invariant line strain model. The β₁ precipitates have the Burgers orientation relationship. The formation of metastable β₁ and stable β₂ particles is considered from the free energy approach of Menon, Banerjee, and Krishnan.     

X-ray photoelectron spectroscopy and scanning auger microprobe studies on oxidation-induced embrittlement mechanism of liquid-phase-sintered 95W-Ni-Fe alloy

The oxidation-induced embrittling mechanism of 95W-Ni-Fe alloy has been studied by X-ray photo-electron spectroscopy (XPS) and scanning Auger microprobe (SAM). Results show that when the alloy oxidizes, WO₂ and WO₃ form around the surface of tungsten particles, and Fe in the bonding phase oxidizes into Fe₂O₃ and FeO on the surface layer of the specimen; thus, surface layer embrittlement occurs as a result of bonding failure between the W particle and the bonding phase. The O diffuses into the matrix of the alloy along interfaces and predominantly segregates on some interfaces, and at the same time, O oxidizes Fe in the bonding phase, thus leading to interface embrittlement and the formation of a bulgy spheroidal fracture.     

Formation of Nuclei With {111}<110> and {111}<112> Orientations of IF Steel at Early Stage of Recrystallization Using EBSD Analysis

The excellent deep drawability of interstitial free steel (IF steel) is closely related to its texture formed during recrystallization. The nucleation process of cold rolled IF steel at the early stage of recrystallization was investigated by electron back scattered diffraction (EBSD). The characteristics of the microstructure after deformation and the orientation of nucleation were observed. The results show that the deformed microstructure with 80% reduction could be subdivided into two groups. These two types of microstructure were characterized by their orientation and internal local misorientations. The nuclei with γ-orientation preferred to form in deformed bands with γ-orientation and at the boundaries between deformed grains with different orientations. The recrystallized grains with {111}<110> orientation appeared firstly in deformed matrix with {111}<112> orientation and consumed the matrix with {111}<112> to grow up, while the recrystallized grains with {111}<112> orientation were observed secondly in deformed matrix with {111}<110> orientation and consumed matrix with {111}<110> to grow up.     

Microstructural aspects of the dissolution and melting of Al2Cu phase in Al-Si alloys during solution heat treatment

The dissolution and melting of Al₂Cu phase in solution heat-treated samples of unmodified Al-Si 319.2 alloy solidified at ≈10 °C were studied using optical microscopy, image analysis, electron probe microanalysis (EPMA), and differential scanning calorimetry (DSC). The solution heat treat-ment was carried out in the temperature range 480 °C to 545 °C for solution times of up to 24 hours. Of the two forms of Al₂Cu found to exist,i.e., blocky and eutectic-like, the latter type is more pronounced in the unmodified alloy (at ≈10 °C) and was observed either as separate eutectic pockets or precipitated on preexisting Si particles, β-iron phase needles, or the blocky Al₂Cu phase. Dissolution of the (Al + Al₂Cu) eutectic takes place at temperatures close to 480 °C through frag-mentation of the phase and its dissolution into the surrounding Al matrix. The dissolution is seen to accelerate with increasing solution temperature (505 °C to 515 °C). The ultimate tensile strength (UTS) and fracture elongation (EL) show a linear increase when plotted against the amount of dissolved copper in the matrix, whereas the yield strength (YS) is not affected by the dissolution of the Al₂Cu phase. Melting of the copper phase is observed at 540 °C solution temperature; the molten copper-phase particles transform to a shiny, structureless phase upon quenching. Coarsening of the copper eutectic can occur prior to melting and give rise to massive eutectic regions of (Al + Al₂Cu). Unlike the eutectic, fragments of the blocky Al₂Cu phase are still observed in the matrix, even after 24 hours at 540 °C.     

Solidification behaviour of Al particles embedded in a Zr Aluminide matrix

A hyperperitectic Al-50 wt% Zr alloy has been manufactured by melt spinning, and the resulting microstructure has been examined by transmission electron microscopy. As-melt spun and annealed hyperperitectic Al-50 wt% Zr consist of a Zr aluminide matrix and an Al rich phase distributed in the form of small and large particles with sizes ∼ 15 and ∼ 100 nm, and as an irregular layer at the cell and grain boundaries. Diffraction analysis of the Zr aluminide matrix is consistent with the aluminide having a tetragonal unit cell with a = 4.014 Å and c = 17.32 Å, similar to equilibrium D0₂₃ tetragonal ZrAl₃ but with a different stoichiometry and different atomic ordering on alternate (004) planes. The Al rich particles show a (001)_Al (001)_Matrix; [100]_Al [100]_Matrix orientation relationship with the Zr aluminide matrix. The solidification nucleation kinetics of the Al rich particles have been examined by heating and cooling experiments in a differential scanning calorimeter over a range of heating and cooling rates. Solidification of Al rich particles is nucleated catalytically on the Zr aluminide matrix at an undercooling in the range 0–5 K. Analysis of the solidification nucleation kinetics of the Al rich particles supports the hypothesis that the classical spherical cap model of heterogeneous nucleation breaks down at low undercoolings and small contact angles.     

Processing and Mechanical Properties of Cast Al (Mg,Mn)-Al2O3 (MnO2) Composites Containing Nanoparticles and Larger Particles

The composites reinforced with nanoparticles result in improved strength and ductility while those containing coarser particles of micron size have limited ductility. The present study investigates the outcome of mechanical properties in a composite reinforced simultaneously with coarse and fine particles. High energy milling of manganese dioxide particles with excess of aluminum powder ensures that nanoparticles generated, either of MnO₂ or alumina, are mostly separate and surrounded by aluminum particles. The milled powder when added to aluminum alloy melt, the excess aluminum particles will melt leaving behind separate oxide nanoparticles without significant agglomeration. Different amounts of milled powder mix have been stirred into molten aluminum alloy where nanoparticles of MnO₂ react with melt to form alumina. The resulting slurry is cast into composites, which also contains coarser (nearly micron size) alumina particles formed by internal oxidation of the melt during processing. The microstructure of the composites shows good distribution of both the size categories of particles without significant clustering. The oxide particles are primarily γ-alumina in a matrix of aluminum-magnesium-manganese alloy containing some iron picked up from the stirrer. These composites fail during tensile test by ductile fracture due to debonding of coarser particles. The presence of nanoparticles along with coarser particles in a composite improves both strength and ductility considerably, presumably due to delay in debonding of coarser particles to higher stress because of reduced mismatch in extension caused by increased strain hardening in presence of nanoparticles in the matrix. The composites containing only coarser oxide particles show limited strength and ductility attributed to early debonding of particles at a relatively lower stress due to larger mismatch in extension between matrix and larger particles. Higher addition of powder mix beyond a limit, however, results in deterioration of mechanical properties, possibly due to clustering of nanoparticles. The present work, however, did not optimize the relative amounts of the different sized particles for achieving maximum ductility.