Tungsten oxide interaction

XPS and Electrochemical Studies on Tungsten-Oxidizer Interaction in Chemical Mechanical Polishing... 

Leclercq, L., Almazouari, A., Dufour, M., and Leclercq, G. 1996. Carbide-oxide interactions in bulk and supported tungsten carbide catalysts for alcohol synthesis. In Chemistry of transition metal carbides and nitrides, ed. S. T. Oyama, 345-61. Glasgow Blackie. 

The interaction of tungsten oxide with silica is weak, but is strong with titania, and intermediate with ceria and zirconia. 

Application of Raman spectroscopy to a study of catalyst surfaces is increasing. Until recently, this technique had been limited to observing distortions in adsorbed organic molecules by the appearance of forbidden Raman bands and giant Raman effects of silver surfaces with chemisorbed species. However, the development of laser Raman instrumentation and modern computerization techniques for control and data reduction have expanded these applications to studies of acid sites and oxide structures. For example The oxidation-reduction cycle occurring in bismuth molybdate catalysts for oxidation of ammonia and propylene to acrylonitrile has been studied in situ by this technique. And new and valuable information on the interaction of oxides, such as tungsten oxide and cerium oxide, with the surface of an alumina support, has been obtained. 

The measurements are performed in a non-interacting hydrocarbon solvent (e.g. cyclohexane) whose molecular mass is close to that of the donor (e.g. pyridine) in order to cancel out contributions from a dispersion component to the measured enthalpy [25]. As an example, the acid strength of tungsten oxide supported on a silica gel has been determined by this method [26]. 

Electrochemical interaction between the oxidizer and the metal is believed to play a key role in material removal in tungsten CMP. In this study, we use X-ray Photoelectron Spectroscopy (XPS) in conjunction with electrochemical measurements in both in-situ polishing conditions as well as in static solutions, to identify the passivation and dissolution modes of tungsten. Dissolution of tungsten oxides was found to be the primary non-mechanical tungsten removal mechanism in CMP. 

Huang X, Zhai HJ, Waters T, Li J, Wang LS (2006) Experimental and theoretical characterization of superoxide complexes [W O iO " )] and [WjO,(O W)] Models for the interaction of O with reduced W sites on tungsten oxide surfaces. Angew Chem Int Ed 45 657... 

Europium oxide interacts with stainless steel (grain boundary attack) above 500°C, to form europium silicate. No interaction occurs even at 1230°C when the silicon content of the steel is less than 58 ppm. Molybdenum or tungsten could be used as protective barriers, since these metals do not react with EU2O3 at elevated temperatures. ... 

Rhenium oxide supported on alumina is easily reduced compared to tungsten oxide on alumina, denoting a smaller interaction between carrier and promoter. ... 

Andersson, K.M. and Bergstrom, L., DLVO interactions of tungsten oxide and cobalt oxide surfaces measured with the colloidal probe technique, J. Colloid Interf. Sci.. 246, 309, 2002. 

The X-ray photoelectron spectrum of Na,W03 (x = 0.547) can be explained by assuming the presence of the three oxidation states for tungsten +6, -1-5, and -1-4. Electrochemical reduction of Na2W04-W03 has been studied and a reappraisal of the electrolysis given in which the tungsten species interacts directly with the cathode according to one of the following equations ... 

An equivalent process is the tungsten oxide-catalyzed interaction of epoxides and peracetals <89JCS(P1)1031). An example is the condensation of styrene epoxide and the peracetal of benzaldehyde to give 3,6-diphenyl-1,2,4-trioxane. 

Oxides are normally stable at the operating temperatures necessary to enhance the interaction between their surface and the gas phase, much more stable compared to organic materials. They are normally operated between 500 and 800 K where the conduction is electronic and oxygen vacancies are doubly ionized. Different oxides have been proposed for conductometric chemical sensors, the most studied is by far tin dioxide that has also been commercialized in form of thick film sensors. Other oxides studied are titanium oxide, tungsten oxide, zinc oxide, indium oxide and iron oxide, first in form of thick and then in form of thin films. Furthermore, the use of mixed oxides, as well as the addition of noble metals, has been studied to improve not only selectivity but also stability. 

Titanium dioxide exhibits optical properties very similar to those of tungsten oxide. Electrons in the conduction band become localized by the electron-phonon interaction and give rise to polaron absorption. Coatings of titanium oxide are less stable in an electrochromic device than films of tungsten oxide, and have therefore not been used so much. 

A cobalt-tungsten interaction species was also detected when cobalt was supported at pH 5 over a 12% WO3/AI2O3 composite [26]. However, a portion of cobalt could not be reduced to the metallic state, although Co in C0WO4 was totally reducible to metallic Co. It was shown that the Co-W interaction species were also present on C0/WO3 catalysts (Impregnation pH 2) and on a commercial cobalt/tungsten oxide compound and that these species were the active catalytic centers in the conversion of Hj and CO to methane. 

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