Chromium cadmium selenide

Cadmium chromium(III) selenide can be prepared by the direct combination of the elements or by the reaction of cadmium selenide with chromium(III) selenide. Crystals of cadmium chro-mium(III) selenide have been prepared by flux growth1 in cadmium chloride, by vapor transport,2 and by a liquid-transport method3 with a platinum metal catalyst. The synthesis given... 

Although high-purity cadmium and selenium are commercially available, high-purity chromium(III) chloride is not. Therefore, if high-purity cadmium chromium(III) selenide is desired, it is best to make chromium(III) chloride by passing chlorine over high-purity chromium metal at high temperatures (ca. 1200°C.). 

The ampul is removed from the furnace and opened. Caution. Hydrogen selenide vapors are formed during the washing, and it is advisable that this operation also be performed in a hood. The crystals of cadmium chromium(III) selenide can be washed in water to remove the cadmium chloride. The crystals are black octahedra which vary in size up to about 3 mm. on an edge. The only impurities detected in these crystals by arc emission spectrographic analysis were Mg and Cu, and these are present only in amounts of less than 20 p.p.m. Anal. Calcd. for CdCr2 Se4 Cd, 21.1 Cr, 19.5 Se, 59.3. Found Cd, 20.8 Cr, 17.7 Se, 58.6. 

Cadmium chromium(III) selenide is a ferromagnetic semiconductor with a Curie temperature of 130 K. Crystals grown by this method are p type. Cadmium chromium(III) selenide has the spinel structure with a cubic cell edge of 10.75 A. 

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. 

Samarium selenides. Reductive cleavage of ArSeSeAr by samarium is catalyzed by a great number of metal halides bismuth(III) chloride, cadmium chloride, chromium(IIl) chloride, cobalt(II) chloride, potassium iodide, and titanium(lV) chloride. The resulting samarium arylselenides readily react with various organic halides. 

From the nineteenth century other pigments might be admixed or substituted for lead antimony oxide, such as cadmium yellow (cadmium sulfide) and lead chloride oxide (qq.v.). Modem paints called Naples yellow typically contain substitutes based on cadmium sulfide (or sulfide selenide) with yellow ochre or red iron oxide and a white pigment such as lead, titanium dioxide or zinc white chromium/nickel titanium yellows and those based on (parachloro-)orthonitraniline are also used (Carlyle, 2001 Wainwright et al.). 

Cadmium sulfides and selenides group Tin sulfides group Tungsten group Berndtite Cassiterite Chromium tin oxide Cobalt tin oxide Copper tin oxide Herzenbergite Lead antimony tin oxide Lead tin oxide Lead tin silicon oxide Ottemannite Romarchite Tin chromate Tin(IV) oxide Tin(IV) sulfide Bronze colours-, Egyptian blue Lead tin yellow Mosaic gold Mosaic silver, Tin white... 

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