Copper Tungstate Research Articles

Solid-phase synthesis of cupric tungstate

The high degree of mixing of W and Cu phases in copper tungstates makes them an attractive source for manufacturing W–Cu composite powders. Hydrogen reduction of copper tungstates provides composite W–Cu powder products with a uniform, homogeneous dispersion of the metal phases. This paper presents test results for a variety of solid-phase reactions to synthesize cupric tungstate (CuWO4). Hydrated, dehydrated, and complex oxides of tungsten and copper have been used as solid reactants. With stoichiometric ratios of reactants, synthesis in air at 800 °C produced 96% to 100% conversion to CuWO4. Heterogeneous synthesis of CuWO4 with the participation of three solid phases (S1 + S2 →S3) required the simplest, most inexpensive equipment. The end product properties of synthesized CuWO4 could be controlled by the proper choice of reactants.

Phase Composition of Electrospark Tungsten Carbide-Based Coatings after Heating and Isothermal Soaking

A study of phase formation on electrospark coatings with WC ― Co ― Cu electrodes on R6M5 high-speed steel during isothermal heat treatment at the operating temperature of the coating. Copper tungstate CuWO 4has been found to form, with its crystal lattice coherently bound to the basic carbide phase of the coating, tungsten monocarbide, through tungsten semicarbide as intermediary. The results complement the data on phase formation during the application of WC-based coatings and during their subsequent use with sliding friction.

The antiferromagnetic structure of copper tungstate, CuWO4

Copper tungstate becomes antiferromagnetically ordered below 23.0(2) K and its magnetic structure has been determined from single-crystal unpolarized neutron diffraction measurements at 5 K. The chemical unit cell is triclinic P1, with a=4.694(1), b=5.830(1), c=4.877(1) AA, alpha =91.64(1), beta =92.41(2) and r=82.91(1) degrees at 15 K. The magnetic propagation vector is (1/200) and the magnetic space group P2a1. The two equivalent copper ions within the unit cell have magnetic moments of 0.67(1) mu B aligned ferromagnetically at the spherical polar angles Theta =121(2) degrees and phi =52(2) degrees , the polar axis being parallel to c and phi being measured from the c-a* plane. This direction coincides, within experimental error, with the axis of elongation of the Jahn-Teller distorted octahedron of oxygen atoms about the Cu2+ ion. A multipole refinement of the moment distribution, to order two on quantum axes Z parallel to the moment direction and X, Y directed towards the four close oxygen neighbours, shows that Y20 is the only significant multipole. Its sign indicates that the moment distribution approximates to an oblate ellipsoid of revolution with its axis parallel to Z. Only two of six oxygen neighbours of the Cu2+ ion carry a significant transferred moment of 0.06(1) mu B. These observations are related to the exchange paths and covalency in the compound.

Electrochemical characteristics of copper tungstate single crystals

Fabrication and characterisation of photoelectrochemical solar cells employing flux-grown copper tungstate single crystals have been accomplished. Mott-Schottky plots have been drawn to provide a useful estimation of the properties of CuWO4 from the measurements, and thus the nature and the values of the parameters ND, EC, EF and EV of the semiconductor have been determined. The J-V characteristics of the crystal in contact with KCl/H2SO4 electrolyte are discussed with reference to the charge transfer mechanism operative at the interface.

Electrical conduction in copper tungstate

Electrical conduction in copper tungstate

Sintering of tungsten-copper composites of various origins

In the presence of a liquid phase the most active sintering was exhibited by W-Cu composites produced from copper tungstate (43% Cu) and from an oxide mixture annealed in air (20% Cu). The reason for this was that air-annealing preceding reduction completely (composite 2) or partially (composite 4) transformed the mechanical mixtures of oxides into homogeneous compounds. Under these conditions the tungsten and copper were “mixed together” at an almost atomic level, which imparted a high degree of homogeneity and dispersion to the W-Cu charges after reduction. In compacts from such a charge a disperse structure with a copper matrix readily forms in the initial stage of sintering, and it is this structure that ensures a high rate of densification. The dependence of the degree of homogeneity of a W-Cu charge on method of preparation was found to be reflected in an increase in the mean pore size in the initial stage of sintering. As expected, the mean pore size grew only negligibly in the initial stage of sintering of compacts from the most homogeneous charges (composites 2 and 4), while in composites 5 and 6 the increase in pore size constituted a serious obstacle to macroscopic shrinkage.

Kinetics of the Solid State Reaction between CuO and WO3

Abstract The solid state reaction of CuWO4-x formation from CuO and WO3 was studied by the contact method in air and nitrogen. The results showed that the reaction is governed by the diffusion of the W6+ and O2- ions and that the rate determining step is the diffusion of oxygen ions in the reaction product. This is in agreement with the defect structure of copper tungstate, an n-type semiconductor with oxygen vacancies through which the diffusion process is possible.

Solubilities of the molybdates and tungstates of silver and copper(II) in water by ion-selective electrodes

The solubilities of silver molybdate, silver tungstate, copper molybdate and copper tungstate in water have been determined over the temperature range 20–40°C using ion-selective electrodes. The molar heats of solution for these salts have been calculated at 25°C. The discrepancies between our data and the existing literature values have been discussed.

Primary Lithium‐Metallic Oxysalt Organic Electrolyte Batteries

The results of a systematic research carried out in our laboratories on the cathodic properties of various metallic oxysalts coupled with lithium in organic electrolytes are discussed. On the basis of these results, silver tellurate, silver molybdate, silver tungstate, copper molybdate, and copper tungstate, respectively, are selected as the most promising of the series and their performances are analyzed in view of applications in high energy primary lithium power sources.

The controlled reduction of copper tungstate in H2O/H2 mixtures

The controlled reductions of copper tungstate, copper tungstate plus blue tungsten oxide and CuO plus WO3 have been studied at temperatures of 500, 600 and 700δC using H2/H2O mixtures in a glass thermobalance. The copper-tungsten oxide composite powder products have been characterized by X-ray diffraction analysis and scanning electron microscopy. The morphologies of the copper-tungsten oxide products have been related to the morphologies of copper-tungsten powders obtained by dry hydrogen reduction. It is shown that widely varying copper-tungsten oxide morphologies may be obtained as precursors for metal powder production by control of the H2/H2O ratio in the reducing gas mixture.

Copper-tungsten composite powders by the hydrogen reduction of copper tungstate

Copper-tungsten composite powders by the hydrogen reduction of copper tungstate

Copper-tungsten composite powders by the hydrogen reduction of copper tungstate

The reduction of two different samples of copper tungstate at 500, 600 and 700° C has been studied using thermogravimetry, X-ray diffraction analysis and electron optical techniques. The morphologies of the resultant Cu-W powders have been related to the morphologies of the original tungstate samples and to the time and temperatures of reduction. The reduction mechanism of the tungstate has been shown to be equivalent to the reduction of pure tungsten oxides once the initial metallic copper phase has been produced. The end products of reduction are mixtures of β-W and Cu at 500° C and α-W and Cu at 600 and 700° C.

A note on the study of the magnetic susceptibility of copper tungstate

A note on the study of the magnetic susceptibility of copper tungstate

Dextran as a source of liver glycogen and blood reducing substance.

In earlier experiments in this laboratory it has been observed that dextran, fed to human subjects, is not recovered in the stools. Engstrom and Aberg have suggested that some of the dextran administered intravenously might be excreted into the gastrointestinal tract where it could be destroyed by bacterial action. Our own observations on dextran incubated with stools suggested that dextran disappears only very slowly, but Hehre has since shown that there are large numbers of anaerobic bacteria present in the intestinal flora, and that it is these, rather than the aerobes, that are capable of splitting dextran. Although ingested dextran may be in part degraded and consumed by the intestinal bacteria, it still seemed to us of interest to learn more about the disappearance of dextran fed by mouth. The following experiments show that dextran feeding leads to a sustained increase in blood sugar and a rise in liver glycogen in the fasted rat, and brings about an increase in the blood sugar of human subjects. Experimental. Male albino rats of the Sprague-Dawley strain, weighing 250-350 g were fasted for 24 hours. A group of 10 control animals were killed and both fractions of liver glycogen were determined by the method of Bloom, Lewis and Schumpert. Glycogen was determined (as glucose equivalent) by means of the anthrone reaction. The fasted experimental animals were given 5 ml of 18% dextran in 0.9% saline by stomach tube. An initial blood sample was taken from the cut end of the tail and additional samples were taken at intervals after feeding. Copper tungstate filtrates were prepared and reducing substances were determined by the method of Nelson. In a series of four rats, both total and fermentable reducing substances were determined. Two or four hours after feeding, the rats were anesthetized with Nembutal and the liver was removed and immediately frozen and powdered. Trichloroacetic acid-extractable and total glycogen was determined on aliquots of the well-mixed liver powder. In order to determine whether glycogen or dextran might be present, other samples were allowed to stand at room temperature for 1.5 to 2 hours in order that glycogenolysis might occur. Dextran was added to parallel samples in order to determine whether dextranolysis could occur in the liver preparation.