Showing papers on "Copper published in 1990"
TL;DR: In this article, a new family of oxygen anionic conductors, exhibiting high performances at low temperature, has been prepared and characterized, derived from Bi4V2O11 by partial substitution of vanadium by other metallic ions.
327 citations
TL;DR: In this paper, the effects of potassium and copper promotion on the activity and selectivity of precipitated iron catalysts for Fischer-Tropsch synthesis (FTS) were studied in a fixed bed reactor at 148 MPa and 235-265 C using synthesis gas with a H{sub 2}/CO = 1 molar feed ratio.
Abstract: The effects of potassium and copper promotion on the activity and selectivity of precipitated iron catalysts for Fischer--Tropsch synthesis (FTS) were studied in a fixed bed reactor at 148 MPa and 235--265{degrees} C using synthesis gas with a H{sub 2}/CO = 1 molar feed ratio It was found that both potassium and copper increase the catalyst activity for FTS and the water gas shift reaction Potassium promotion ({approximately} 02--1 wt %) results in an increase in the average molecular weight of hydrocarbon products and suppression of secondary reactions (olefin hydrogenation and isomerization of 1-alkenes to 2-alkenes) Copper promotion ({approximately} 3 wt %) has a similar effect on the hydrocarbon distribution, but it enhances slightly the secondary reactions The activity of doubly promoted (100 Fe/3 Cu/{ital x}K, {ital x} = 02 or 05) catalysts was higher than that of singly promoted catalysts and was independent of potassium loading, whereas their selectivity behavior was strongly influenced by their potassium loading Product selectivities on the 100 Fe/3 Cu/02 K catalyst were similar to those of the 100 Fe/3 Cu catalyst, whereas selectivities of the 100 Fe/3 Cu/05 K catalyst were similar to those obtained in tests with the 100 Fe/05 K catalyst
270 citations
267 citations
TL;DR: In this article, 50 nm tantalum films were sputtered onto unpatterned single-crystal 〈100〉 Si wafers and overlaid with 100 nm Cu.
Abstract: We have investigated the effectiveness and failure mechanism of thin tantalum layers as diffusion barriers to copper. 50 nm tantalum films were sputtered onto unpatterned single‐crystal 〈100〉 Si wafers and overlaid with 100 nm Cu. Material reactions in these films were followed as a function of annealing temperature by in situ resistance measurements, and characterized by Rutherford backscattering spectroscopy and cross‐section transmission electron microscopy. While pure Cu on Si reacts at 200 °C, the Ta film prevents Cu silicon interaction up to 600 °C. At higher temperatures, reaction of the Si substrate with Ta forms a planar layer of hexagonal TaSi2. Cu rapidly penetrates to the Si substrate, forming η‘‐Cu3Si precipitates at the Ta‐Si2‐Si interface.
259 citations
244 citations
TL;DR: In this article, the reaction between copper and silicon is studied using differently oriented Si and Cu, and an orientation dependence is observed for the Cu-Si reaction, with different phases of the silicides formed.
Abstract: The reaction between copper and silicon is studied using differently oriented Si and Cu. Copper films, deposited by electron‐beam evaporation at room temperature without intentional heating of the substrates, show an epitaxial relation with the Si substrates, resulting in (100)‐ and (111)‐oriented Cu films on the (100) and (111) Si, respectively. An orientation dependence is observed for the Cu‐Si reaction, with different phases of the silicides formed. At 200 °C, for example, the silicide formation rate is about five times faster for the (100)‐oriented structures than for the (111) ones. An interface bonding model is used to relate to the orientation dependence observed, and is compared with previous work on the Au‐Si and Au‐Cu systems. The diamond structure of Si favors the (100) surface for reaction, as is observed for the Au‐Si reaction. The face‐centered‐cubic structure of Cu, however, favors the (111) orientation for reaction. The latter is observed for the Au‐Cu reaction using epitaxial Cu films on...
224 citations
01 Feb 1990
TL;DR: In this paper, copper titrations were conducted at sea using differential pulse anodic stripping voltammetry on North Pacific samples to determine the extent of copper complexation with organic ligands.
Abstract: The complexation of trace metals by organic ligands has long been proposed to play a significant role in determining trace metal speciation in seawater. However, analytical methodologies with sufficient specificity and sensitivity only recently have been developed to enable us to address questions of trace metal/organic complexation. In this study copper titrations were conducted at sea using differential pulse anodic stripping voltammetry on North Pacific samples to determine the extent of copper complexation with organic ligands. This study includes data from a transect from 33°N, 139°W to 55°N, 148°W and seasonal occupations of the VERTEX T-4 station (33°N, 139°W). The data indicate the presence of at least two copper binding ligands: L 1 , the stronger ligand, or ligand class, averages 2 nM with log K ′ l cond(Cu′) = 11.6; L 2 , the weaker ligand class varies between 5 and 10 nM witgh log K ′ 2 cond(Cu′) = 8.6. The presence of these ligands strongly buffers the activity of copper(II) in surface waters at all stations. Seasonal variations in the distribution of strong copper complexing ligands follow seasonal variations in the depth of the mixed layer at T-4 and indicate a ligand source in the lower mixed layer. Ligand concentrations do not covary with the rates of primary productivity in a latitudinal transect from the central North Pacific to the subarctic. Ligand concentrations at all stations vary only by a factor of two and hold surface water copper(II) ion activities relatively constant (about 10 −14 M), suggestive of a regulated ligand production mechanism. These results comprise a unique data set for copper complexation in the Pacific and may have significantly implications for the distribution of plankton between oligotrophic and subarctic systems.
216 citations
210 citations
IBM1
TL;DR: The solid state reaction between copper and silicon has been studied using Rutherford backscattering, glancing-angle x-ray diffraction, scanning electron microscopy, and x−ray photoemission spectroscopy as discussed by the authors.
Abstract: The solid state reaction between copper and silicon has been studied using Rutherford backscattering, glancing‐angle x‐ray diffraction, scanning electron microscopy, and x‐ray photoemission spectroscopy. Schottky‐barrier‐height measurements on n‐type Si (100) have also been performed in the temperature range of 95–295 K with the use of a current‐voltage technique. The results show that a metal‐rich compound with a composition in the Cu3Si range forms at low temperatures (473 K). The electronic properties of the compound are dominated by the hybridization between the Cu(d) and Si(p) valence states. A direct consequence of this hybridization is the peculiar oxidation behavior of the compound surface; both Cu and Si have been found to oxidize at room temperature. The oxidation of Si in the silicide is enhanced as compared with the oxidation of the elemental single‐crystalline Si surface. Upon annealing the oxidized surface, a solid state reaction takes place: Cu2O disappears and a thicker SiO2 layer grows, o...
193 citations
185 citations
TL;DR: In this article, optical absorption studies have been made on some square planar pink CuN 4 2− chromophore complexes to investigate solute-solvent interaction, if any, spin-Hamiltonian constants of the copper(II) ion; metal-ligand bond parameters; and the environment around the copper-II ion.
TL;DR: In this article, a copper nitride thin film was prepared by using the ion-assisted deposition in which accelerated nitrogen ions were irradiated during the deposition of copper metal, and the degree of nitrification of the film was controlled by changing the ion current density.
Abstract: Copper nitride thin films were prepared by using the ion-assisted deposition in which accelerated nitrogen ions were irradiated during the deposition of copper metal. The degree of nitrification of the film was controlled by changing the ion current density. The reflection coefficient of the prepared copper nitride films decreased with the increase of the ion current density. The reflection coefficient was about 30% at 780 nm wavelength, and it recovered to 70% after the film was heated at 300°C. The preliminary experiment of write-once optical recording of this film was carried out, and the viability of its practical use in new media was confirmed.
TL;DR: In this article, it was concluded that copper-ammine complexes held on the surface of the zirconia support exist in three different states, viz., isolated and clustered copper(II) ions and tetraamminecopper (II) nitrate.
TL;DR: GSH is proposed as a likely candidate for copper donation to Cu-free,Zn-superoxide dismutase in vivo and a very stable complex in the presence of oxygen and a more efficient copper donor to the copper-free enzyme than other low molecular weight Cu(II) complexes.
TL;DR: In this article, a silica-supported copper catalysts have been prepared by means of deposition-precipitation under both atmospheric and hydrothermal conditions, and the catalysts show a mean metal particle size gradually increasing from 3 to 8 nm as the metal loading increases.
TL;DR: In this paper, a model was proposed to explain the effect of zinc oxide on copper in terms of a reversible transfer of hydrogen between copper and zinc oxide, and it was suggested that therate determining step normally occurs on the surface of the copper but that the rate of reaction can be dependent on the availability of spillover hydrogen from the zinc oxide.
Abstract: The experimental observation that the activity of a series of zinc oxide supported copper catalysts is related to the surface area of the copper is examined in the light of recent evidence that hydrogen spillover from copper to zinc oxide is facile. A model is proposed which explains the effect of zinc oxide on copper in terms of a reversible transfer of hydrogen between copper and zinc oxide. It is suggested that therate determining step normally occurs on the surface of the copper but that therate of reaction can be dependent on the availability of spillover hydrogen from the zinc oxide.
TL;DR: The copper-free apoenzyme, prepared by dialysis of lysyl oxidase against alpha,alpha'-dipyridyl in 6 M urea, catalyzed neither the oxidative turnover of amine substrates nor the anaerobic production of aldehyde at levels stoichiometric with enzyme active site content, thus contrasting with the ping pong metalloenzyme.
TL;DR: The energy levels of the copper atom, in all stages of ionization for which experimental data are available, have been compiled in this article, and the energy levels, either experimental or theoretical, and experimental g-factors are given leading components of calculated eigenvectors are listed.
Abstract: The energy levels of the copper atom, in all stages of ionization for which experimental data are available, have been compiled Ionization energies, either experimental or theoretical, and experimental g‐factors are given Leading components of calculated eigenvectors are listed
TL;DR: In this paper, two methods to determine copper complexation in estuarine waters were compared, one based on a complete titration of the complexing capacity of the sample and the other on measurement of the labile and total dissolved metal concentrations only.
TL;DR: In this article, the influence of small amounts of copper on the neutron-irradiation-induced embrittlement of reactor pressure vessel steels is investigated using fluorescence extended X-ray absorption spectroscopy.
Abstract: The influence of small amounts of copper on the neutron-irradiation-induced embrittlement of reactor pressure vessel steels is of considerable current interest. Previous work has shown that the embrittlement is associated with the formation of copper-rich precipitates, but uncertainties remain regarding their composition and form. This Letter reports the preliminary results from a structural investigation of such precipitates in solution-treated and thermally aged Fe–-Cu and Fe–-Cu–-Ni model alloys using fluorescence extended X-ray absorption spectroscopy. The most significant result is the first direct observation that small clusters in the peak hardness condition have a b.c.c. structure.
TL;DR: In this article, a simple and efficient low-cost transfer system was described which allows electrochemical manipulation and transfer of specimens into the vacuum analysis chamber under an inert atmosphere under the inert atmosphere.
Abstract: X-ray photoelectron spectroscopy was employed to study surface films generated by anodic electrochemical oxidation of copper in Na 2 SO 4 solutions at pH=12. A simple and efficient, low-cost transfer system is described which allows electrochemical manipulation and transfer of specimens into the vacuum analysis chamber under an inert atmosphere
TL;DR: In this paper, the correlation of T c with copper or oxygen bond valence sums for a wide range of superconducting cuprates is shown to contradict the behaviour observed for YBa 2 CU 3 O x as x is varied from 6 to 7.
Abstract: The recently demonstrated correlation of T c with copper or oxygen bond valence sums for a wide range of superconducting cuprates is shown to contradict the behaviour observed for YBa 2 CU 3 O x as x is varied from 6 to 7. This conflict is removed by introducing two independent variables, namely, the sum of and difference of the copper and oxygen bond valence sums. The latter is a measure of the hole density on the CuO 2 plane and as this increases T c passes through a maximum T c (max). The former indicates the relative distribution of these holes on the oxygen or copper sites for a given compound. T c (max) correlates closely with the preference for hole distribution on the oxygen atoms. A general phase-diagram using these bond sum parameters is presented.
TL;DR: In this article, the authors showed that the higher the initial cupric concentration, the more important is this complexation reaction, and that the ion exchange sites were relatively saturated and reached 308 and 101 mmol/kg d.w.
TL;DR: In this article, the growth and reactivity of oxide films on copper in solutions of high pH were investigated, and a brief survey of the electrocatalytic performance of copper anodes in base was also carried out.
Abstract: The objective of the present work was to reinvestigate the growth and reactivity of oxide films on copper in solutions of high pH; a brief survey of the electrocatalytic performance of copper anodes in base (which will be reported shortly) was also carried out