Au In Cu Research Articles

Grain-boundary diffusion and segregation of gold in copper: Investigation in the type-B and type-C kinetic regimes.

Grain-boundary (GB) impurity diffusion of Au in Cu has been investigated by the radiotracer serial-sectioning technique using the $^{195}\mathrm{Au}$ isotope with high specific activity. Measurements in the temperature ranges 618 to 1036 K and 450 to 526 K were carried out in Harrison's type-B and type-C regimes, respectively. In the type-B regime, the product P=${\mathit{sD}}_{\mathrm{GB}}$\ensuremath{\delta} was determined (s being the segregation factor, ${\mathit{D}}_{\mathrm{GB}}$ the GB-diffusion coefficient, \ensuremath{\delta} the GB width), while in the type-C regime ${\mathit{D}}_{\mathrm{GB}}$ values were measured directly. Combining the obtained P and ${\mathit{D}}_{\mathrm{GB}}$ values and assuming \ensuremath{\delta}=0.5 nm, the Au GB-segregation factor was evaluated. From the temperature dependence of s, the segregation enthalpy ${\mathit{H}}_{\mathit{s}}$=-9.7 kJ ${\mathrm{mol}}^{\mathrm{\ensuremath{-}}1}$ has been obtained. GB self-diffusion in Cu in the type-B regime has also been studied by the same experimental technique using the tracer $^{64}\mathrm{Cu}$. The obtained ${\mathit{D}}_{\mathrm{GB}}$=P/\ensuremath{\delta} values for self-diffusion are systematically larger than ${\mathit{D}}_{\mathrm{GB}}$ values for Au in Cu, whereas for lattice diffusion the opposite interrelation holds. This observation is discussed in terms of a trapping of Au atoms during impurity GB diffusion.

溶融金および金-銅合金中の希薄亜鉛の活量測定

The activities of Zn in dilute solution with molten Au and Au-Cu alloy have been measured by the use of an isopiestic method at 1423 K, and the first and second order interaction parameters between Zn and Cu in molten Au have been determined.Additions of Cu to Au-Zn binary alloy increase the activity of Zn. The activities of Zn in the Au-Cu-Zn ternary molten alloys are well expressed by Wagner’s relation taken into account the second order terms, in the composition range NZn+NCu≤0.10. It has been demonstrated that the quadratic formalism proposed by Darken is valid for this system in the composition range, NCu≤0.08 and NZn<0.07.Activity coefficient of Zn at infinite dilution of Zn in Au-Cu binary solvent varies with NAu⁄NCu smoothly, and seems to be qualitatively in accordance with the prediction from the equation formulated by Richardson.

X-ray-diffraction study of a thermomechanically detwinned single crystal of YBa2Cu3O6+x.

A twin-free single crystal of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$ has been studied at room temperature and 115 K by x-ray-diffraction analysis. The crystal was grown from an Y-Ba-Cu-O melt in a gold crucible, leading to a 2% substitution of Au for Cu. Twins were removed from the as-grown crystal by a novel thermomechanical process, resulting in an orthorhombic (Pmmm), single-domain crystal. Oxygen positions and occupancies in the Cu-O basal plane have been refined, showing that the O(5) site is completely vacant, and the O(4) atoms are offset from the crystallographic mirror plane positions by 0.15 \AA{} in a zig-zag fashion. Gold, which is a common impurity in crystals grown by the present technique, was found to occupy Cu(1) sites only. Weak superlattice reflections suggest a possible three-dimensional ordering of O and/or Au. To our knowledge, this paper reports the first high-resolution x-ray study of an intentionally detwinned, superconducting ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$ single crystal.

Channeling measurement of solute vibration amplitude in an alloy.

Computer simulations are used to show how measurements of ion channeling may be very sensitive to differences in thermal vibration amplitude between solute and host atoms in an alloy. Application is made to the measurements of Alexander and Poate on an alloy of \ensuremath{\sim}2 at. % Au in Cu, and it is concluded that the vibration amplitude of Au is 86% as large therein as that of Cu.

Atomic motion of copper in solid Au:xCu alloys studied by nuclear magnetic resonance

The atomic diffusion of Cu in solid Au:xCu alloys (x=5.7, 8.2, 9.1, 10.4, 13.2, 17.3 at.%) has been studied by means of solute (63Cu) nuclear spin relaxation (NSR) experiments in the rotating frame (T1p) between ambient temperature and 1100 K. Surprisingly, two distinct diffusion-induced maxima in the relaxation rate could be observed. The high-temperature mechanism around 950 K corresponds to the translational diffusion of Cu in the solid solution phase, as is suggested by comparison with tracer diffusion data. The second relaxation mechanism occurs at fairly low temperatures ( approximately=700 K) with a maximum intensity around 8 at.% Cu. The origin of this contribution to the diffusional NSR rate is not quite clear. The authors attribute it to a short-range ordering effect of Cu atoms in the Au matrix. The activation enthalpies of both types of atomic motion depend only slightly on the Cu concentration.

Quantitative Auger analysis of complex electrical contact alloy materials

Addition of elemental Auger spectra has been used to produced several series of Auger lineshapes versus composition for the ovelapping peaks resulting from mixtures of Cu, Pt, Pd or Ag in Au; S in Au or Pt, Cl in Au, Pt or Pd; C (both graphitic and carbidic) in Au, Pt, Ag or Pd. These assorted lineshapes series may be used to obtain semi-quantitative analysis of overlapping peaks by matching lineshapes, but have also been used to calibrate peak ratios versus composition in order to quantitatively separate contributions to overlapping Auger peaks. This procedure is illustrated by application to the quantitative analysis of tw electrical contact alloys - ASTM B541. Advantages and limitations of this procedure are B540 and ASTM B541. Advantages and limitations of this procedure are discussed.

Cupriferous bogs of the Coed y Brenin area, north Wales and their significance in mineral exploration

A number of bog areas with richly cupriferous peats have been outlined during a geochemical soil survey investigating the distribution of Cu, Mo, Pb and Zn in the vicinity of the Coed y Brenin porphyry copper deposit. During the first half of the last century considerable amounts of peat were extracted from the bog known as “Turf Copper” and ash derived from burning this peat was smelted as a source of Cu. “Turf Copper” bog is situated immediately to the west of the main outcrop of porphyry-style mineralization in this area. In addition, three small Cu bogs were delineated in the area of Bryn Coch to the south of the main mineralized zone, where disseminated Cu mineralization outcrops. Waters draining into the bog areas are enriched in Cu up to 0.97 mg/l. Analysis of profile samples from the bogs has indicated extreme enrichment in Cu and variable enrichments in Mo, Pb, Zn, Mn, Co, Ag and Au. Mineralized intrusive rocks in this area are significantly enriched in Cu and Au. The enrichment of Cu, up to 5.72%, and Au, up to 0.13 ppm in ashed peat samples, reflects the mobilization of these elements from adjacent mineralization by ground and surface waters and their fixation by interaction with organic matter accumulated in the bogs. The recognition of cupriferous bogs and the sampling and analysis of peats, including analysis for Au, may provide useful indicators of Cu and Au mineralization, especially in glaciated areas where mineralization may be masked by transported overburden and geochemical anomalies displaced by hydromorphic agencies.

Surface melting and surface segregation on spherical Cu-Au crystals grown from a drop of melt

Observations of surface melting on spherical crystals of clean copper or gold were extended to Cu-Au alloys. A deep layer of surface melt can be identified optically between the molten and solid portions of remelting Cu-Au crystals. The diluted component (Cu in a matrix of Au or Au in Cu) is segregated into surface melt. Areas around the (111) and (001) poles remain free from surface melt and prove to possess a self-cleaning force against the diluted component.

Zener relaxation in copper-gold alloys

Measurements of the Zener relaxation in copper-gold alloys, both in single crystals and in polycrystalline specimens, are reported. The data has been taken at low (1 Hz), intermediate (70 Hz) and high (50kHz) frequencies. The temperature, orientation and concentration dependence, of both the relaxation strength and the relaxation time, have been studied in detail, for composition up to 25 at.% Au in Cu. Finally, the results are discussed in terms of current theories of anelastic effects produced by stress-induced ordering.

Deviation from Matthiessen's rule at high temperatures: Theoretical interpretation

Theoretical interpretation is given for the deviation from Matthiessen's rule (DMR) at high temperatures on dilute alloy systems Au in Cu, Cu in Au, and Ni in Cu, and Cu, Ag, and Ge in Al, measured with the use of the new experimental techniques developed by Fujita and others. The measured deviation from this rule, $\ensuremath{\Delta}(c, T)$, can be fitted to curves of $Y+AT$ ($Y\ensuremath{\approx}0$), where $T$ is the absolute temperature, and the numerical constant $A(Y)$ can be calculated using a standard lowest-order (higher-order) variational scheme. $Y$ is always positive and gives a measure of the anisotropy of the scattering at high temperatures. For most of the Al-based and noble-metal-based dilute alloys, $Y$ is small and the anisotropy scattering is unimportant. The proportionality factor $A$ has been evaluated, within the standard variational formalism, using an atomistic model calculation for the electron-phonon spectral function. It is shown that the leading contribution to the high-temperature DMR is due to the change in the phonon spectral function $F(\ensuremath{\omega})$ for Cu in Al, Ge in Al, Cu in Au, and Au in Cu alloys, while it comes from the change in the electron-phonon coupling function ${\ensuremath{\alpha}}_{\mathrm{tr}}^{2}(\ensuremath{\omega})$ (electron-mass-enhancement parameter ${\ensuremath{\lambda}}_{\mathrm{tr}}$) for the Ag in Al alloy.

Deviation from Matthiessen's rule at high temperatures: Au in Cu, Cu in Au, and Ni in Cu

Deviation from Matthiessen's rule at high temperatures: Au in Cu, Cu in Au, and Ni in Cu

The temperature dependence of the isotope effect for self-diffusion and cobalt impurity-diffusion in gold

Measurements of the self-diffusion and the isotope effect of 195Au and 199Au in gold as well as the isotope effect of 57Co and 60Co impurity-diffusion in gold are reported. A significant decrease of both types of isotope effects with increasing temperature is observed, which is attributed to a divacancy contribution to the total diffusion rate. At 1323 K D∗2vD∗ ⋍ 0.2 is deduced. This result is supported by the small curvature near Tm of the Arrhenius plot of the self-diffusion data. For cobalt impurity-diffusion via divacancies an isotope effect E2vCo ⋍ 0.3 is estimated at Tm. Assuming the validity of the jump frequency model for impurity-diffusion in fcc metals it is concluded from additional isotope effect experiments of Co in Cu and Au in Cu, that the mass dependence of the ΔK factor should be very small.

Impurity-host force-constant changes fromAu197Mössbauer recoilles-fraction measurements for dilute Cu(Au) and Ag(Au) alloys

The absolute /sup 197/Au Moessbauer absorber recoilless fraction f/sub a/ has been measured for two dilute gold-alloy systems. These systems were 2-at. percent Au in Cu and 5-at. percent Au in Ag. For the Cu(Au) alloy, measurements were made over the temperature range 4.2 to 100/sup 0/K. For the Ag(Au) system, the recoilless fraction was measured only at 4.2/sup 0/K. For example, at 4.2/sup 0/K, f/sub a/ = 0.239 +- 0.003 for Cu(Au), and f/sub a/ = 0.195 +- 0.008 for Ag(Au). The recoilless-fraction measurements are interpreted in terms of the impurity-atom lattice-dynamical model of Mannheim. In terms of this model, values were obtained for the effective nearest-neighbor force constant ratios ..gamma../sub Au-Cu//..gamma../sub Cu-Cu/ and ..gamma../sub Au-Ag//..gamma../sub Ag-Ag/. For both alloy systems, the atomic coupling between the gold atom and the host metal is found to be enhanced relative to the host-host coupling. In obtaining these estimates, host phonon density-of-states functions determined for neutron inelastic scattering measurements were used.

Vibrations of a mixed crystal: Neutron scattering fromNi55Pd45

The crystal dynamics of an alloy with a large amount of mass disorder (Ni and Pd have masses 58.7 and 106.5 amu, respectively) have been investigated by inelastic neutron scattering. A triple-axis spectrometer was used to measure the phonon dispersion curves and widths in a crystal of the fcc random alloy ${\mathrm{Ni}}_{55}$${\mathrm{Pd}}_{45}$. Significant broadening was observed in each branch for neutron groups corresponding to phonons of large wave vector. For transverse modes, many of the widths are large and indicate behavior characteristic of resonance modes. Neutron groups for [111] transverse vibrations at the zone boundary had the largest widths (2.1 THz, compared with a mean frequency of 3.3 THz). The widths of the longitudinal modes are generally smaller than those of transverse modes, and no definite indications of resonance behavior are apparent. The results are compared with the predictions of several theories, notably the coherent-potential approximation with some qualitative success. The form of the discrepancy between theory and experiment, and the similarity of the results to those of an experiment on crystals containing relatively dilute concentrations of Au in Cu, suggest the need to consider force-constant changes as well as mass disorder. Some new measurements for Cu(Au) are also reported.

THE SUPERLATTICE FORMATION AND LATTICE SPACING CHANGES IN COPPER-GOLD ALLOYS

A thorough investigation of the Cu-Au system has been taken by means of X-ray diffraction studies. Alloys were annealed at appropriate temperatures for different periods (one month, three months, six months and one year) and slowly cooled down to room temperature, or quenched at 300° and 600℃, with the purpose to elucidate the phases and the phase transformations that might occur. Lattice parameters were accurately determined in order to study their variations with compositions and heattreatments. The stacking periods of the ordered structures with long periods were investigated, particularly in their relations to compositions and temperatures, and by means of quenching alloys after having been annealed for various periods of time, the ordering process near the equiatomic composition was studied. Under the conditions of heattreatment mentioned above, the entire system consists of six different phases: α 1 is the primary solid solution of Au in Cu, α′ 1 the superstructure corresponding to Cu 3 Au, α 2 the primary solid solution of Cu in Au, α′ 2 the superstructure corresponding to CuAu 3 , k the superstructure corresponding to CuAu I, and k′ the superstructure corresponding to CuAu II. The most noteworthy is the fact that with the increase of the period of annealing, the ordered regions extend gradually, while the two-phase regions gradually narrow down, and in the slowly cooled alloys after one year's treatment, the two-phase regions almost disappear. This leads the authors to conceive that the two-phase coexistence in the Cu-Au system is in a state of metastable equilibrium. As for the α′ 2 phase, the most clear superlattice lines appear not at the stoichiometric composition but at 68 at.% Au. The k′ phases which appear at both sides of the equiatomic composition are partially transformed into k phases after the alloys being treated for one year. By the equiatomic composition, both the maximum transformation temperatures of the k phase and the k′ phase are not exactly at the equiatomic composition but at 49 at.% Au or even less.The measurement of lattice spacings shows that: the relation between the mean lattice spacings of the fundamental unit cells and the compositions is a continuous curve indicating positive deviation from Vegard's law. In the a and a′ regions, a increases with the Au content. In the k′ regions, for alloys where the Au contents are less than that in the equiatomic composition, a increases with the Au content while c decreases, and meanwhile c/a deviates gradually from 1 ; and for alloys where the Au contents are more than that in the equiatomic composition, a decreases gradually with the increase of the Au content, while c increases abruptly, and c/a gradually approaches 1. At the compositions where k′ transforms into k or vice versa, both a and c undergo abrupt changes.The influence of the period of annealing to lattice spacings has been fully considered. The lattice spacings in those parts of the phase regions wherein the phases do not change with the heattreatment are practically unchanged within the experimental conditions cited above. In the α′ 2 region, the transformation from disorder to order causes sharp drop in the lattice spacing. In the k regions, for alloys where the Au contents are less than that in the equiatomic composition, a increases with the period of annealing; and for alloys where the Au contents are more than that in the equiatomic composition, both a and c decrease with the increase of the period of annealing. But in all k regions, the volume of the fundamental unit cell decreases with the increase of the period of annealing. The authors are therefore of the opinion that the volume of the fundamental unit cell should be taken as a general measure of the degree of order.The law governing the indices of the superlattice lines present in the k′ structures has been discussed in details as well as their correspondence to those present in the k structure. The stacking periods in the k′ structures have been accurately determined by measuring the distances between the doublets arising from the splitting of the k superlattice lines as k is transformed into k′. The variation of stacking periods with compositions is continuous. The farther the alloy is from the ideal composition, the longer is the stacking period. And for the same alloy, the higher the temperature, the longer the stacking period. The stacking period may be odd, and may be a non-integer.In the metastable two-phase regions, not only the lattice parameters, but also the stacking periods of the k′ phase vary with compositions. The two-phase coexistence is composed really of two structural forms with the same composition. Purely from ther-modynamic considerations, it has been shown that the order-disorder transformations in the Cu-Au system are transformations of the second order.

Axial ratio changes in H.C.P. ζ phases in the systems AuInCu and CuGeAu

The lattice spacings of hexagonal close-packed ζ phase alloys of compositions falling along lines of constant electron concentration in the ternary systems AuInCu and CuGeAu have been determined accurately with an estimated precision of 1 in 15,000. It is found that the axial ratio remains constant with increasing gold or copper content along constant electron concentration lines for values greater than 1.36 in both AuInCu and CuGeAu alloys. These differing trends are discussed in terms of the possible electronic structures and in the light of previous studies of binary ζ phases. The decreasing trends in axial ratio are believed to be associated with the presence of Brillouin zone overlaps which occur in the higher ranges of electron concentration.

Experiments on the resistance minimum the effects of certain solutes in copper, silver and gold

Abstract In en attempt to increase the knowledge of what chemical impurity atoms give rise to a resistance minimum in copper, silver and gold as solvents, we have examined dilute polycrystalline solid solutions of Ni, Cu, and Sn in Au, Sn in Ag, and Mg in Cu, which were of some interest. It appears that none of these particular solutes causes a resistance minimum in the solvents specified. This finding is discussed in relation to previous work.