Silver Tungstate Research Articles

A thin layer, solid-state, primary Li�Ag2CrO4 polymer battery

The majority of lithium polymer batteries under development use intercalation compounds as cathode materials [1]. The lithium-intercalation compound combination benefits from high cyclability, but suffers from sloping charge and discharge voltage profiles. In previous work we have described some new types of lithium polymer batteries based on nonintercalation cathode materials which involved LilAg2WO 4 or LilCuWO4 couples [2]. The use of these electrochemical systems in combination with a highlyconducting polymer electrolyte membrane, allowed the fabrication of thin-layer, laminated batteries having very interesting features, such as flat, highvoltage discharge curves, high-rate discharge capability and a limited but significant cycling life. Considering these promising results, we have extended the study by considering the LilAg2CrO4 electrode system, which, although used in liquid electrolyte batteries [3], to our knowledge has never been tested in solid-state, lithium polymer electrolyte batteries. Silver chromate is expected to be more promising cathode material than silver tungstate both in terms of cost and of specific capacity. The results describing the fabrication of this new type of LilAg2CrO 4 polymer battery and its electrochemical evaluation, are illustrated and discussed in this work.

Kinetics and mechanism of solid state reactions of silver tungstate with mercuric bromide and mercuric chloride

The kinetics and mechanism of the Ag 2WO 4HgBr 2 and Ag 2WO 4HgCl 2 reactions have been studied in the solid state. The kinetics have been carried out by a visual technique. Both the reactions follow the parabolic rate law X 2 = Kt, where X is the thickness of product layer at time t and K is the parabolic rate constant. The kinetics have been studied at several temperatures, for different lengths of air-gap between the two reactants and for different particle sizes of the reactants. It has been demonstrated that diffusion in both the reactions is predominantly controlled by the vapour phase, but diffusion by surface migration is also significant. In order to understand the mechanism of the reactions, X-ray powder diffraction, chemical analysis, conductivity and thermal studies have been carried out. Silver tungstate reacts with mercuric bromide and mercuric chloride in the molar ratio 1:1 to give AgBr, HgWO 4 and AgCl, HgWO 4, respectively, as the end products.

ChemInform Abstract: Kinetics and Mechanism of Reactions of Silver Tungstate with Mercuric Bromoiodide and Mercuric Chlorobromide in the Solid State.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Kinetics and mechanism of reactions of silver tungstate with mercuric bromoiodide and mercuric chlorobromide in the solid state

The kinetics and mechanism of the Ag 2WO 4-HgBrI and Ag 2WO 4-HgClBr reactions were studied by X-ray diffraction, thermal and electrical conductivity measurements. The kinetics were studied at several temperatures and for different lengths of air- gap between the two reactants. The kinetic data fit the equation X n = Kt, where X is the thickness of the product layer at time t and n and K are constants. Silver tungstate reacts with mercuric bromoiodide and mercuric chlorobromide in the molar ratio 1:1 to give Ag(Br,I), HgWO 4 and Ag(Cl,Br), HgWO 4, respectively, as the end products.

Studies on silver tungstate-mercuric lodide reaction in solid state

The kinetics and mechanism of reaction of silver tungstate with rhombic and tetragonal mercuric iodide in solid state have been studied using X-ray diffraction, chemical analysis, and electrical conductivity measurements. The reaction is diffusion controlled and the data for lateral diffusion best fit the equation X n = kt. Activation energies suggest that rhombic HgI 2 is more reactive toward Ag 2 WO 4 than its tetragonal form. The reaction rate that rises abruptly near the transition temperature records a smooth rise with increase in temperature both below and above this temperature.

Heat capacity of silver tungstate between 80 and 500 K

Heat-capacity measurements at constant pressure are reported for silver tungstate between 80 and 500 K, from 80 to 300 K by adiabatic calorimetry and from 300 to 500 K by d.s.c. A small anomaly is apparent with a maximum near 276 K. Some results are also presented for the solid electrolyte Ag 6I 4WO 4 and these are compared with the summed heat capacities of the constituents: (4AgI + Ag 2WO 4), of the electrolyte.

Anomalous behavior of saturated aqueous tungstate solutions

Potentiometric measurements on a freshly prepared saturated silver tungstate solution at 25°C indicate the existence of at least four different ionic tungstate species in this solution leading to the formation of a four-component precipitate. Solubility measurements have been carried out on saturated aqueous silver tungstate solutions at 25°C at different ionic strengths and at various pH. An attempt is made to explain the appearance of the solubility curves. Conductivity measurements on saturated sodium tungstate solutions indicate a phase transition of solid sodium tungstate at 36.5±1.0°C. The assumption of a phase transition is supported by DTA and TGA measurements.

The high rate discharge characteristics of silver chromate, silver molybdate, and silver tungstate cathodes in molten nitrate electrolytes

Silver chromate, silver molybdate, and silver tungstate are promising solid cathode materials for molten nitrate electrolyte thermal battery cells. All three compounds show open circuit potentials more positive than the reversible Ag +/Ag couple. The dominant reduction process for all three cathodes at high rates is clearly the reaction to form metallic silver. Potentiostatic discharges at −0.200 V versus the 0.1 m Ag +/Ag reference indicates that all three cathode materials are capable of sustaining high current densities. Galvanostatic studies show that all three cathodes are capable of sustaining current densities over 500 mA cm −2 without excessive polarization. Cell discharges using lithium anodes demonstrate that the Ag 2CrO 4, Ag 2MoO 4 and Ag 2WO 4 cathodes can provide a practical alternative to the AgNO 3 cathode for high rate, molten nitrate electrolyte thermal batteries.

Microprobe study of enhanced Raman scattering effect on WO 3/Ag thin films

Enhanced Raman scattering effect on WO 3 thin films, sputtered on a silicon substrate coated-silver thin film, has been evidenced using the MOLE microprobe. The silver surface is very rough and the observed ERS effect seems to be due to the formation of tungsten bronze at the WO 3/Ag interface. Thermal treatment favours silver diffusion in the WO 3 film and the formation of silver tungstate.

Standard potentials of the silver—silver tungstate, silver—silver phosphate, and silver—silver arsenate electrodes in water—dioxane and water—urea mixtures and related thermodynamic functions

The standard potentials of the silver—silver tungstate, silver—silver phosphate and silver—silver arsenate electrodes in four different compositions of water—dioxane and water—urea mixtures at seven different temperatures from 5 to 35°C have been determined from EMF measurements of cells of the type Ag(s), AgCl(s), NaCl(c)//Na x Z(c/ x), Ag x Z(s), Ag(s), where x is 2 or 3, and Z is WO 4, PO 4 or AsO 4. These values have been used to evaluate the transfer thermodynamic quantities accompanying the transfer of 1 g ion of WO 2− 4. PO 3− 4 or AsO 3− 4 ion from the standard state in water to the standard state in water—dioxane or water—urea mixtures.

Effects of Processing Methods on the Contact Performance Parameters for Silver-Tungsten Composite Materials

A comparative study of electrical, mechanical, and microstructural properties of silver-tungsten contact materials (49 and 64 volume percent Ag) prepared by two different processing methods, namely press-sinter (PS) and press-sinter-infiltrate (PSI), is reported. Even with the same elemental composition, tungsten particle size and distribution, the two different techniques of preparation have resulted in no difference in electrical contact resistance, minor differences in microhardness, transverse rupture strength and thermal expansion, and significant differences in contact life and arc erosion properties. Oxidation weight gains at 600°C and 700°C are similar but the oxide layer morphology is quite different at 700°C. The oxidation rate at 700°C is more than ten times of that at 600°C. Silver tungstate is found to be absent at 700°C. High contact resistance is due to the formation of porous tungsten oxides and a porous tungsten layer where silver is removed by the electric arc. The arc erosion is dependent on crack formation and propagation which are not fully understood.

Solubility of Silver Tungstate in Aqueous Sodium Nitrate Solutions with Different pH Values at 25 degrees C. Evaluation of a Solubility vs. Ionic Strength Relation Valid for Ionic Strength up to 1.0 mol dm^-3.

Solubility of Silver Tungstate in Aqueous Sodium Nitrate Solutions with Different pH Values at 25 degrees C. Evaluation of a Solubility vs. Ionic Strength Relation Valid for Ionic Strength up to 1.0 mol dm^-3.

Thermodynamics of the silver—silver tungstate, silver—silver phosphate and silver—silver arsenate electrodes in aqueous medium at different temperatures

Thermodynamics of the silver—silver tungstate, silver—silver phosphate and silver—silver arsenate electrodes in aqueous medium at different temperatures

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.

Solubility of Silver Tungstate in Aqueous Solutions at Different Ionic Strengths and Temperatures. Thermodynamic Quantities of Ag2WO4.

Solubility of Silver Tungstate in Aqueous Solutions at Different Ionic Strengths and Temperatures. Thermodynamic Quantities of Ag2WO4.

Physicochemical Properties of Silver Tungstate

Physicochemical Properties of Silver Tungstate

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 Switching Performance of Refractory Carbide-Silver Contacts

Eight refractory carbide-silver contacts have been evaluated for switching performance: WC-Ag (WC 40 volume percent); WC-AG-Co ((a)WC 45 volume percent, Co 7 volume percent, (b) WC 35 volume percent, Co 7 volume percent); TiC-Ag ((a)TiC 80 volume percent, b) TiC 60 volume percent, c) TiC 48 volume percent); and NbC-Ag ((a)NbC 72 volume percent b) NbC 48 volume percent). The contacts were placed in an experimental switch and were operated to make and break a 20-A 110-V resistive circuit. The contact resistance was monitored at 0, 1000, 2000, and 3000 switching operations by measuring the temperature rise at the fixed contact terminal after 20 A had been flowing for ½ h. The contact surfaces were examined using a scanning electron microscope. The performance of the WC-Ag was similar to that which was previously observed with W-Ag contacts; high contact resistances were measured after only 1000 operations. The WC-Ag-Co contacts showed consistently lower contact resistance values than were observed for the WC-Ag contacts. The TiC-Ag and NbC-Ag contacts performed about as well as the WC-Ag-Co contacts did. These data showed that the presence of carbon in the WC-Ag contacts did little to alleviate the problem of high contact resistance values resulting from insulating oxides of W and Ag forming on the contact surfaces. The presence of Co, on the other hand, resulted in conditions which were not favorable to the formation of the silver tungstate. The TiC-Ag data showed that Ag was always present on the contact surfaces together with TiC and with oxides of titanium; there was no evidence of the formation of silver titanate. The NbC-Ag data were similar to the TiC-Ag data. After continued switching, however, the TiC and NbC contacts began to form a surface skin of refractory material on the contact surface. The relative merits of these refractory carbide-silver contacts are discussed.

Effect of the electric arc and the ambient air on the contact resistance of silver, tungsten, and silver-tungsten contacts

Contact pairs of Ag, W, and Ag-W were operated 6000 times in a 20-A 110-V ac circuit. The effect of contact-resistance change was observed by measuring the temperature rise (TR) at the fixed contact while passing the steady-state 20 A. The TR was measured before the switching had begun and after each 1000 operations. A large number of contact pairs were used in order to ensure a good statistical interpretation of the data. The chemical composition of the contact surfaces was measured using a Debye-Scherer x-ray analysis. The distribution of contact resistance for Ag contacts remained the same throughout the experiment. For W contacts, the distribution was initially higher than that for Ag: the result of conductivity and hardness differences. During the switching experiments, the formation of tungsten oxides on the contact surface resulted in high contact-resistance values. For Ag-W, the distribution was initially closer to that for Ag contacts: the result of a thin surface layer of Ag on the Ag-W. During the switching, the Ag-W contact-resistance distribution gradually increased in dispersion and had higher values than those measured for W contacts. The x-ray data showed that not only were tungsten oxides formed, but also there was a high probability that some of the free Ag on the contact surface formed an insulating silver tungstate.

(W 4O 16) 8− Polyion in the high temperature modification of silver tungstate

The high temperature form of silver tungstate, Ag 8W 4O 16, contains tetratungstate ions in which the tungsten atoms are coplanar and each is octahedrally coordinated to oxygen atoms. Two octahedra share three edges with other octahedra and two octahedra share two edges with other octahedra. Four types of coordination for the Ag + ion are found in the structure: distorted triangular prismatic (with an additional more distant oxygen through a quadrilateral face), octahedral, tetrahedral, and twofold linear. These have been observed before in different crystals, but not all in the same crystal. The deviation from centrosymmetry of the polyion appears to be highly stable as deduced from unsuccessful attempts to reverse the polarization of the crystal. Crystals of Ag 8W 4O 16 are orthorhombic, belong to space group Pn2n (C 10 2v) with lattice constants a=10.89, b=12.03, c=5.92 A ̊ all ±0.02 A ̊ and contain 2 Ag 8W 4O 16 per unit cell. X-ray diffraction data obtained with a Buerger-Supper single crystal automatic diffractometer were used to determine the crystal structure.