Ferric selenide

Aluminium and magnesium selenides are very similar light brown powders, unstable in air. Zinc and iron (ferrous) selenides are more stable in air, the zinc compound being citron-yellow and the iron compound black and metallic in appearance.8 The latter becomes brown in air owing to oxidation. Ferric selenide is difficult to obtain pure. Cadmium selenide, which is dark brown, is very stable in colour and is used as a pigment. With thallium, selenium is said to form three distinct compounds,9 but analyses of these compounds have led to discordant results. The selenides of aluminium, chromium and uranium cannot be prepared in the wet way. Nickel selenide, unlike the sulphide, shows no tendency to form a colloidal solution. 

Ferric selenide or iron sesqui-selenide, Fe2Se3, was obtained by Little 2 by heating iron to redness in selenium vapour, cooling, and fusing the product with excess of selenium under a layer of borax. It also results when hydrogen selenide is passed over ferric oxide at red heat.3 It is a grey crystalline powder. 

The potentiostatic electrodeposition of iron selenide thin films has been reported recently in aqueous baths of ferric chloride (FeCb) and Se02 onto stainless steel and fluorine-doped TO-glass substrates [193], The films were characterized as polycrystalline and rich in iron, containing in particular a monoclinic FesSea phase. Optical absorption studies showed the presence of direct transition with band gap energy of 1.23 eV. 

This compound is readily obtained by the action of potassium hydro-selenide on an aqueous solution of pyramidone chloride. It forms pale yellow, hard needles, melting at 196° C., sparingly soluble in cold water, readily soluble in alcohol, chloroform, benzene or dilute acids. The aqueous" solution gives a faint yellowish-red turbidity with ferric chloride, and a yellow colour with sulphur dioxide. The hydrochloride is a crystalline product, melting at 177° C., and deliquescent in air. The mercurichloride and platinichloride are white and yellowish-red precipitates respectively. When a chloroform solution of seleno-pyramidone is treated with chlorine, the dichloride is formed, which has the constitution ... 

Iron diselenide, FeSe2, is prepared by heating anhydrous ferric chloride to dull red heat in hydrogen selenide.3 When ignited in oxygen, it yields ferric oxide and selenium dioxide. 

The behavior of selenium in soils mirrors that of the pure oxides (Goldberg, 1985). In acid soils, selenium is likely to occur mainly as Se(lV) strongly adsorbed to iron oxides. Less commonly, Se(IV) may form highly insoluble iron compounds such as ferric selenite (Fe2(0H)4Se03) or iron selenide (FeSe). In alkaline, oxidized and selenium-rich soils, most of the selenium is likely to be present as Se(Vl) which is very weakly adsorbed. Furthermore, there are no common insoluble selenate minerals. Hence, selenate accumulates in soluble form particularly in arid and semi-arid areas where evaporation tends to concentrate selenium along with other soluble salts (Deverel et al., 1994). 

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