Tungsten selenide

Canfield D. and Parkinson B. A. (1981), Improvement of energy conversion efficiency by specific chemical treatments of molybdenum selenide (n-MoSei) and tungsten selenide (n-WSci) photoanodes , J. Am. Chem. Soc. 103, 1279-81. 

The a-furildioxime method has been used for determining nickel in silicate and sulphide minerals [16], tungsten selenide [83], steel [16], indium and aluminium [84], cadmium [85], alkalis [3], beryllium [86], rhenium [87], compounds of rare-earth elements [88,89], petroleum products [90], and boiler water [91]. 

If one wants to use p-type semiconductors where the water reduction can be obtained by illumination, one suffers from the small band gaps and has to apply an auxiliary external voltage. Such systems could be used for a photoassisted electrolysis where only part of the power needed comes from the direct light absorption in the semiconductor electrode. The additional voltage could be taken from a photovoltaic cell coupled in series to the electrolysis cell. A p-type tungsten selenide electrode appears suitable for this purpose because its conduction band is located somewhat above the hydrogen potential in acidic solution. 

Energy conversion has been always a preferred application of thermoelectro-chemical methods. PECs work with semiconductor films in contact with reversible redox couples. Intense sunlight illumination generates free charge carriers and induces a cell voltage. In [172], temperature increase enhances the usable current at a tungsten selenide electrode in contact with iodinefiodide solution. 

Chromium(III) sulfide, CrySs chromium selenide, CrSe chromium(III) telluride, Cr2Tc3 molybdenum(IV) sulfide, M0S2 (molybdenite) molybde-num(IV) selenide, MoSe2 molybdenum(IV) telluride, MoTey tungsten(IV) sulfide,... 

WS2 (tungstenite) tungsten(VI) sulfide, WS3 tungsten(IV) selenide, WSc2 tungsten(IV) telluride, WTe2. 

Relatively few tungsten(Vl) selenide or telluride species are known. Treatment of frani -[W E2(PMe3)4] (E = S, Se, Te) with aldehydes afforded the metalla-oxirane derivative [W E2(PMe3)2(/c -OCHR)] (25). Reaction of species containing WO + with (NH4)2Sx in the presence of 2,1 -dipyridyl (bipy) afforded the mononuclear species [WO(/c -S2)2(bipy)] and reaction of [W02S2] with elemental sulfur and hydrazinium hydrochloride afforded [ WO(A -S2)2 2(/r2-S7)(M2-NH2NH2)] (26). 

Transfer of material from one surface to another is a common phenomenon when surfaces rub against one another, and Rabinowicz suggests that it may be universal in dry contact. Some material combinations are of course much less prone to transfer than others, but Bowden and Tabor describe transfer between a diverse variety of material pairs, inciuding lead selenide and rock-salt, chromium and diamond, tin and platinum, and tungsten, iead or copper and steei. 

Bis-3,4-(trifluoromethyl)-l,2-diselenete 651 is prepared by refluxing selenium with hexafluoro-2-butyne. It reacts with triphenylphosphine and triphenyl-arsine. Triphenylphosphine selenide was isolated, but no other compounds were identified.Ring-opened complexes with nickel, copper, vanadium, molybdenum (652), tungsten, iron, and cobalt are analogous to complexes of the 1,2-dithiete (527) (Section XXXV.2.C.). 

Se chemical shifts span a wide range of ca. 3300 ppm the extremes are marked by selenoaldehydes, some molybdenum selenides, and cationic heterocycles (up to S = 2434) at the high-frequency end and bridging selenium (p) in tungsten complexes (3 = —900) at the low-frequency end. A detailed discussion of electronic influences on Se chemical shifts and its variation in different classes of compounds has been published. In the following, some general characteristic tendencies are collected. 

Some epidemiological studies report data from populations exposed to selenium in the food chain in areas with high selenium levels in soil. It is likely that selenite, selenate, and the selenium found in food and in dietary supplements comprise the majority of selenium compounds to which oral, off-site selenium exposures will occur at or near hazardous waste sites. Aside from the variation in effective dose, the health effects from exposure to selenate, selenite, and dietary selenium are not expected to differ greatly. However, oral exposures to many other compounds of selenium could occur (primarily through soil or edible plant ingestion) if those compounds were deposited at the site, or if local environmental conditions greatly favor transformation to those forms. Heavy metal selenides, aluminum selenide, tungsten diselenides, and cadmium selenide are used in industry and may end up in waste sites. 

Alumina catalysts activated by additions of dehydrogenating catalysts, e.g., nickel oxide, copper oxide or sulfide, zinc oxide or sulfide, cobalt selenide, zinc phosphate, cadmium tungstate, mixtures of the oxides of zinc and tungsten, of cadmium and molybdenum, etc., are claimed to be superior in the formation of acetaldehyde from mixtures of steam and acetylene at 350° to 400° C.l-la Zinc oxide catalysts may be activated in a similar way by the addition of small amounts of molybdates or molybdic acid, and are effective at 300° to 350° C.121b... 

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