Showing papers on "Copper published in 1975"

Monovacancy formation energy in copper, silver, and gold by positron annihilation

Abstract: Monovacancy formation energies in copper, silver, and gold have been deduced from the temperature variation of the peak counting rate in the angular correlation curve of positron annihilation radiation from these metals. The counting rate was temperature dependent over the entire temperature range, including temperatures so low that no trapping of positrons at vacancies is effective. At these temperatures the increase in counting rate results from thermal expansion of the lattice. By separating this thermal expansion effect from the vacancy trapping effect at higher temperatures, we obtained values for the monovacancy formation energyE 1v for copper, silver, and gold to 1.29±0.02 eV, 1.16±0.02 eV, and 0.97±0.01 eV, respectively.

Optical constants of copper and nickel as a function of temperature

Abstract: The optical constants were determined for copper and nickel from reflection and transmission measurements on vacuum-evaporated thin films, in the spectral range 0.5-6.5 eV and at temperatures of 78, 293, and 423 K. The imaginary part of the dielectric constant was nearly independent of temperature for nickel, but for copper it increased with temperature in the intraband region below 2 eV and decreased above 4 eV in the interband region. Interpretation of the increase below 2 eV according to the Drude free-electron expression suggests a temperature and frequency dependence of the relaxation time, which is not completely explained. The thermal behavior in the interband region can be largely understood, however, if the zero-temperature theory of Williams, Janak, and Moruzzi is modified by including a Debye-Waller factor in transitions between nearly-free-electron-like bands.

A model of the dump leaching process that incorporates oxygen balance, heat balance, and air convection

Abstract: A one dimensional, nonsteady-state model of the copper waste dump leaching process has been developed which incorporates both chemistry and physics The model is based upon three equations relating oxygen balance, heat balance, and air convection It assumes that the dump is composed of an aggregate of rock particles containing nonsulfide copper minerals and the sulfides, chalcopyrite and pyrite Leaching occurs through chemical and diffusion controlled processes in which pyrite and chalcopyrite are oxidized by ferric ions in the lixiviant Oxygen, the primary oxidant, is transported into the dump by means of air convection and oxidizes ferrous ion through bacterial catalysis The heat generated by the oxidation of the sulfides promotes air convection The model was used to simulate the leaching of copper from a small test dump, and excellent agreement with field measurements was obtained The model predicts that the most important variables affecting copper recovery from the test dump are dump height, pyrite concentration, copper grade, and lixiviant application rate

The Effect of a Dispersion of Cobalt Particles on High-Temperature Creep of Copper

Abstract: The dependence of the steady-state creep rate, es, on stress, σ, and temperature, T, for pure copper and a two-phase copper–4.04 wt.-% cobalt alloy at 712 K can be described asFor copper, the stress exponent, n, is ∼4.8 and the activation energy for creep, Q c, is ∼ 115 kJ/mol. For the copper–cobalt alloy, n≃5 and Qc≃140 kJ/mol at low stresses, whereas n≃12 and Qc≃210 kJ/mol at high stresses. This variation in n and Q c can be rationalized by measuring the ‘friction stress’, σo, using a technique involving consecutive small stress reductions during creep. Then, for both materialsThe activation energy, Q c *, is derived from the temperature-dependence of es at the same value of (σ – σo) rather than at constant σ as in the determination of Q c. For both materials, Q c*≃110 kJ/mol, indicating that processes occurring in the matrix are rate-controlling during creep of the two-phase alloy. The greater creep-resistance of the copper-cobalt alloy is attributable to the particle dispersion decreasing A* ...

Oxide chemistry. Part II. Ternary oxides containing copper in oxidation states-I, -II, -III, and -IV

Abstract: We report an investigation of the preparation, structure, and magnetic properties of ternary oxides containing copper in oxidation states-I, -II, -III, and -IV. The compounds described are: ACuO2(A = Al or Ga); AcuCo2(A = Ca, Sr, or Ba), A2Cu2O5(A = Sc, Y, Bi, or In), and A2CuO4(A = La, Al, or Ga); BaCuO2·5, ACuO3(A = Y or La); and BaCuO2·63 which is the only phase containing copper(IV) which could be obtained. X-Ray pcv.der patterns have been indexed wherever possible and magnetic-susceptibility measurements from 80 to 300 K are interpreted for all paramagnetic species.

The Application of a Simple Chemical Model of Natural Waters to Metal Fixation in Particulate Matter

Abstract: A simple chemical model was used to investigate the mechanisms controlling the distribution of metals between soluble and particulate fractions in natural waters. The model particulates used were potassium bentonite, hydrous MnO2, and solid humic acid. The soluble species in natural waters were modelled by soluble humic acid, tannic acid, and bicarbonate. The sorption curves for Cu(II), Cd(II), and Zn(II) onto humic acid and MnO2 obeyed Langmuir adsorption isotherms whereas the sorption of the above ions onto bentonite followed a Freundlich isotherm. Chemical analysis of the total model using atomic absorption spectroscopy and differential pulse anodic stripping voltammetry indicated that copper distribution depends on the pH of the suspension: above pH 6.0, 50 % of the copper is sorbed onto the particulates whereas the copper in solution is in a complexed form; between pH 6 and 3.8 the soluble copper is distributed between organic complexes and "free" copper ion; between pH 4.2 to 2.5 copper is being des...

Copper coordination group in blue copper proteins. Evidence from resonance Raman spectra

Abstract: Tunable dye laser excitation in the intense similar to 600-nm absorption band of azurin, plastocyanin, and ceruloplasmin provides resonance enhanced Raman spectra. They consist of a complex set of bands, at least three or four in number, between 350 and 473 cm-1, which are assignable to Cu-N or Cu-O bond stretching, and a weak band near 270 cm-1, which probably arises from Cu-S stretching. A weak band at 765 cm-1 found in plastocyanin may arise from C-S stretching. Analysis of the Raman intensity pattern, as well as of the nature of the resonant electronic transition, leads to a model of the "blue" copper site involving approximately trigonal-bipyramidal coordination, with a sulfur and two nitrogen ligands in the equatorial plane, and less strongly bound nitrogen or oxygen ligands at axial positions. This arrangement would be well poised for stabilization of Cu(I) upon reduction.

The Copper–Selenium System at Temperatures to 850 K and Pressures To 50 Kbar

Abstract: Phase relationships in the copper/selenium system in the composition range 30–70 atomic % selenium have been studied at temperatures from 298 to 850 K and at pressures to 50 kbar. A revised atmosph...

Copper solubility in FeO−Fe 2 O 3 −SiO 2 −Al 2 O 3 slag and distribution equilibria of Pb, Bi, Sb and As between slag and metallic copper

Abstract: The solubility of copper in silica-unsaturated fayalite slags containing an average of about 8 pct Al2O3 was measured by equilibrating the slag with metallic copper at 1200 and 1300°C under CO−CO2 atmospheres with oxygen potentials in the rangepO2=10−6 to 10−11 at. The copper solubility, which was found to be dependent upon the oxygen potential, was expressed in terms of the Fe/SiO2 ratio, temperature and activity of CuO0.5. The distribution of Pb, Bi, Sb and As between copper and slag was measured concurrently by doping the metallic copper. The distribution coefficient was defined by (mole fractionX in metal)/(mole fractionX in slag) assuming the FeO−FeO1.5−SiO2−AlO1.5−CuO0.5 system slag. The distribution coefficient for lead was found to be a function of the oxygen potential, and a PbO activity in the slag of 0.07±0.01 was measured over the range of 1200 to 1300°C. Dissolution of Bi, Sb and As in the slag was found to be independent of the oxygen potential suggesting atomic rather than oxidic dissolution. The observed distribution coefficient for Bi and Sb was 30. The observed distribution coefficient for As was 300, but this is subject to error up to one order of magnitude due to analytical uncertainty of slag. The data are useful in analyzing minor element behavior in copper smelting processes.

The Formation and Structure of Copper(II) Complexes with Cyclodextrins in an Alkaline Solution

Abstract: Copper(II) forms a 2: 1 complex with cyclodextrin in an alkaline solution. The complexes with α- and β-cyclodextrins were isolated from solutions by the addition of ethanol. They are labile, and, upon heating, the Cu(II) is reduced to Cu(0). The role of the hydroxide ion was examined by means of potentiometrie and conductometric titrations; it was found that the reaction of 1 mol of α-cyclodextrin with 2 mol of Cu(OH)2consumes 2 mol of the hydroxide ion, whereas 3 mol of the hydroxide ion are consumed for the reaction of β-cyclodextrin. Polarimetric measurements showed that the optical rotation of cyclodextrin changes from dextrorotatory to levorotatory upon the formation of the Cu(II)-cyclodextrin complex. It was suggested, with a molecular model, that the two pairs of C2 and C3′ secondary hydroxyl groups of contiguous glucose units are cross-linked by the Cu(OH−)2Cu ion bridge in the α-cyclodextrin complex and by Cu(OH−)(O2−)Cu ion bridge in the β-cyclodextrin complex. Furthermore, the circular ring of ...

Tensile strength and work hardening of ultrafine‐grained high‐purity copper

Abstract: Sputter‐deposited high‐purity copper specimens with grain sizes from 8.4 to 0.056 μm were tested in tension to investigate the influence of grain size on yield strength for small grain sizes. The smallest grain size in the sputter‐deposited copper was a factor of 40 smaller than the smallest grain size previously available for yield‐strength–grain‐size studies of high‐purity copper. The 0.2% offset yield strengths varied from 73.4 MPa for the coarsest‐grained copper to 481 MPa for the finest‐grained copper. The hardening was related to grain‐ and twin‐boundary spacings. The yield strength obeyed the Hall‐Petch relation even for the finest grain size of 0.056 μm, giving σy=6.39+3.74(l)−1/2 MPa, where σy is the 0.2% offset yield strength and l is the mean intercept length (mm) between boundaries. The data agreed with the Ashby model, σ∼ (e/l)1/2, only at very low strains (e<0.001) for the specimens with very fine grain sizes (l⩽0.077 μm).