Showing papers on "Tungstate published in 1989"

Identification of tungstate complexes in lithium-tungstate-borate glasses by Raman spectroscopy☆

Abstract: Changes in the Raman spectra of (Li2B4O7)0.5(WO3)0.5 glasses, when prepared under slightly different conditions, are interpreted as arising from tungstate complexes in the glass matrix; one of the observed extra vibrational modes can be correlated with a permanent blue color center which is reminiscent of the electrochemically induced tungsten bronze centers.

Incorporation of tungsten and molybdenum into anodic alumina films

Abstract: The incorporation of tungsten and molybdenum into barrier films on aluminium, formed to 5–350V at 5 mA cm−2 in 0·1 M tungstate and molybdate electrolytes at 298 K, has been studied by Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy (TEM). RBS indicated that tungsten and molybdenum were incorporated at similar constant rates (2·9 × 1013 W atoms cm−2 V−1 and 2·7 · 1013 Mo atoms cm −2 V−1), with the surface layers of all films being enriched with either ∼5 × 1014 W atoms cm−2 or ∼9 × 1014 Mo atoms cm−2. The enrichment was a consequence of immersion in the electrolyte, since similar concentrations of tungsten were picked up by merely dipping electropolished aluminium or anodic alumina films into the tungstate electrolyte. TEM of film sections, assisted by the atomic-number contrast effect associated with incorporated species, revealed that tungsten incorporated into a 50 V film was distributed uniformly in the outer 0·3 of the thickness.

Corrosion inhibition by some oxyanions in coal-water slurries

Abstract: Corrosion rates of AISI 1010 steel samples in coal-water slurries in the presence and absence of chromate, molybdate, and tungstate oxyanion inhibitors were determined by electrochemical and weight loss measurement techniques. The corrosion rates obtained by the electrochemical technique were generally higher than the values obtained by weight loss measurement. The corrosion inhibition efficiencies of chromate, molybdate, and tungstate were almost the same and the shifts infree corrosionpotential suggest that these inhibitors are anodic in nature. Electron microprobe, X-ray photoelectron, and Auger electron data showed the presence of hexavalent molybdenum and tungsten oxides and trivalent chromium oxide species in the films that formed on the surfaces of the samples exposed to solutions containing inhibitor. The amount of inhibitor present in the films decreased in the order chromium > tungsten > molybdenum.

Experimental studies on the ionic (protonic) transport in ammonium para-tungstate pentahydrate

Abstract: Proton transport in ammonium para-tungstate pentahydrate (NH4)10W12O41.5H2O (APT.5H2O) has been established using coulometry transient ionic current IR and electrical conductivity measurements along with the TGA/DTA results of Kiss and co-workers. The mobile ions are NH4+, H+ and O2-. The ions (H+ and O2-) are the products of electrolysis of the inter-layer water. The temperature dependence of the electrical conductivity has been correlated with the accompanying dehydration and de-ammoniation reaction of APT.5H2O.

Anomalous Peak Intensities in the EXAFS of Polynuclear Molybdenum Compounds

Abstract: EXAFS (Extended X-ray Absorption Fine Structure) experiments on various polynuclear molybdate and tungstate compounds revealed the unusual phenomenon that Mo–O peaks which should appear at around 1.9 A in Fourier transforms of the EXAFS spectra for Mo6O192− and PMo12O403− are hardly discernible, while the tungstates and other molybdates give the metal–oxygen peaks normally. It is concluded that the Debye–Waller factors for the metal-bridging oxygen bonds in Mo6O192− and PMo12O403− are exceptionally large (≥0.08 A). The shape of the Raman bands for the Mo6O192− pertaining to the vibration involving the bridging oxygens supports the large σ values estimated. EXAFS measurements were also performed for AsMo12O403−, SiMo12O404−, and PMo12O403−. The compounds with large Debye–Waller factors seem to be unstable against reductants.

A New Laser Host Crystals - Lanthanum Tungstate La2 (WO4)3

Abstract: On presente les resultats preliminaires des investigations de l'action d'un nouveau laser a base de tungstate de lanthane dope au neodyme. Les mesures de fluorescence et d'absorption sont effectuees sur des echantillons a environ 2.4%. On trouve des proprietes qui permettent de bonnes applications pratiques

The Preparation of a New Multinuclear Heteropolytungstate Anion [Fe3Co4W17O70H11]−10

Abstract: The preparation of a salt of a new multinuclear heteropoly tungstate complex is reported. FABMS, analytical and spectroscopic (UV-VIS-IR) evidence is presented which strongly indicates that the new complex is isostructural with [Cu2Fe4W18O70H6]−10, for which the preparation and X-ray structure were reported earlier1. The new salt is tentatively formulated Na10H5[Fe3Co4W17O70H6]·37H2O, wherein one Fe+3 or Co+2 replaces one W+6 in the conventional [X2Z4W18O70] formulation of the earlier structure. Possibilities are thus foreseen for additional complexes, isostructural with the above and involving various combinations of transition metals. Such complexes have potential importance for magnetic interaction and bonding studies as well as for catalysis.

Indirect determination of tungstate in rat tissues by atomic absorption spectrometry.

Abstract: An indirect method is described for the determination of tungsten as tungstate in tissue samples by atomic absorption spectrometry (AAS). Tungstate forms a stable ion-association complex [Fe(dipy)3]2+WO2–4(dipy = 2,2′-dipyridyl) in acidic solution, which can be extracted into chloroform with an efficiency of higher than 98%. The extract can be analysed for iron (and hence indirectly for WO2–4) by flame AAS after stripping back into 60% perchloric acid. The calibration graph is linear up to 19 p.p.m. of WO2–4 and the limit of detection is 0.17 p.p.m. Many foreign ions do not interfere and the method has been applied successfully to the determination of tungstate in rattus norvegicus tissue samples.

Method for refining molybdenum or tungsten

Abstract: PURPOSE:To easily refine Mo by adding pyridyl azo compound and polyethylene glycol-mono-nonyl phenyl ether to an aqueous solution of ammonium molybdate of Mo containing U and Th. CONSTITUTION:The oxide of Mo or W, such as MoO3 or WO3, in whilch the amount of U and Th existing is regulated to >=1ppb is dissolved in aqueous ammonia by heating, by which an aqueous solution of ammonium molybdate or ammonium tungstate is formed. Then, pyridyl azo compound and polyethylene glycol-mono-nonyl phenyl ether are added to the above aqueous solution. At this time, it is preferable to regulate the additive quantities of the former and the latter to about 0.0001-1.0pts.wt. and about 0.05-200pts.wt., respectively, based on 100pts.wt. of MoO3 or WO3. By the above procedure, U, Th, Fe, etc., are taken in micelles together with the above pyridyl azo compound as a scavenger and separated. Subsequently, the above aqueous solution is formed into about 5-10N acid concentration by means of nitric acid to allow molybdic acid or tungstic acid to crystallize out, which is reduced so as to be formed into Mo or W containing

Piezoelectric ceramic and manufacturing method thereof

Abstract: A piezoelectric ceramic mainly composed of a lead system oxide contains at least one of lead iron tungstate (Pb(Fe 2/3 W 1/3 ) O₃), lead copper tungstate (Pb(Cu 1/2 W 1/2 ) O₃), lead cobalt tungstate (Pb(Co 1/2 W 1/2 ) O₃), lead nickel tungstate (Pb(Ni 1/2 W 1/2 ) O₃), and lead zinc tungstate (Pb(Zn 1/2 W 1/2 ) O₃), and an A-site/B-site molar ratio thereof is 1.01 or higher. In a manufacturing method thereof, a mixture of material powders arranged to comprise tungsten oxide an in addition thereof at least one of iron oxide, copper oxide, cobalt oxide, nickel oxide and zinc oxide, having said molar ratio is sintered.

Process for production of pure tungstic acid or molybdic acid from impure alkali metal tungstate or molybdate solutions

Abstract: Acidification of impure alkali or ammonium tungstate or molybdate solutions prior to electrodialysis to produce tungstic acid or molybdic acid is carried out by the addition of pure tungstic acid or molybdic acid as the salts of tungsten isopolyacids or molybdenum isopolyacids, respectively. This is less expensive than using pure HCl or H2 SO4 and prevents contamination with chloride or sulfate ions. The pure tungstic acid or molybdic acid is isolated from the product.

Modification of Zeolite Y by Tungsten Oxide

Abstract: A study of the modification of zeolite Y by WO 3 is described and discussed. Catalysts containing 0.1-10% WO 3 were prepared from impregnation of ammonium meta tungstate onto zeolite Y extrudates. Control of the pH during impregnation was found to be a useful means of preparing samples either uniformly coated with WO 3 or preferentially coated at the extrudate surface. The WO 3 /zeolite Y catalysts were used to investigate 1-hexene cracking at 200 to 380°C. Modification of zeolite Y by WO 3 can lead to improved catalytic activity and promising results were obtained for samples prepared by impregnation at pH 2. 1.

Forming a ceramic coating

Abstract: A method of forming a ceramic coating on a substrate comprises immersing the substrate in an aqueous solution containing a silicic acid compound and/or a metal oxoanion, and irradiating the substrate with a laser beam The laser beam may be a continuous oscillation laser beam, the beam having a pulse width of 05-12ms The silicic acid compound may be sodium silicate, sodium metasilicate, potassium silicate, lithium silicate or colloidal silica The metal oxoanion may be a tungstate, stannate, molybdate, phosphate, vanadate, borate, chromate, aluminate or permanganate In view of the use of a laser beam the process may be carried out at a relatively low temperature, eg 2-100 DEG C

Monooxo-Capped Tritungsten Carboxylate Clusters.

Abstract: An improved method for the preparation of the monooxotritungsten hexaacetate cluster (IIIa) is described starting with Na tungstate (I) as demonstrated in the scheme.