Tellurium tellurides

Sulfation Roasting. Acid roasting technology (Fig. 2) relies on differences in the volatility of the tetravalent oxides of selenium and tellurium at roasting temperatures of 500—600°C to selectively volatilize selenium from slimes. Acid roasting uses sulfuric acid as the oxidant for the conversion of selenium/selenides and tellurium/tellurides to their respective tetravalent oxides. Typical oxidation reactions are as follow ... 

A few reactions were carried out that proved that the telluride anion adds to carbon-carbon triple bonds. The corresponding diorgano telluriums were obtained in low yields. Tellurium, when heated with acetylene, water, and a base, produced divinyl tellurium. Telluride was claimed to be a product of the disproportionation of tellurium3. When this reaction was carried out with aqueous potassium hydroxide and hexamethylphosphoric triamide at 120° in a steel autoclave under 10 atm acetylene, the yield of divinyl tellurium was 30%4. The yield increased to 94% when tin(II) chloride was present in the reaction mixture5 1. 

Te tellurium >Te, tellanediyl =Te, tellanylidene telluroxo tellurium telluride (general) Te -, tellanidyl, telluride( l—) Te2-, tellanediide, telluride(2—) telluride tellurido (general) Te -, tellanidyl, tellurido( l—) Te2-, tellanediido, tellurido(2—)... 

Tellurium Tellurides produce a dense white smoke, part ofwhich passes through the tube and part of (Te) which settles as a thick, white sublimate on the lower side. On heating of the sublimate of TeO, small oil-like drops are formed. 

Selenium and tellurium react similarly, forming selenides and selenates(IV), and tellurides and tellurates(IV) respectively. Like the sulphide ion, S , the ions Se and Te form polyanions but to a much lesser extent. 

Hydrogen selenide (selenium hydride), HjSe, and hydrogen telluride (tellurium hydride), HjTe... 

These closely resemble the corresponding sulphides. The alkali metal selenides and tellurides are colourless solids, and are powerful reducing agents in aqueous solution, being oxidised by air to the elements selenium and tellurium respeetively (cf. the reducing power of the hydrides). 

Tellurium is occasionally found native, but is more often found as the telluride of gold (calaverite), and combined with other metals. It is recovered commercially from the anode muds that are produced during the electrolytic refining of blister copper. The U.S., Canada, Peru, and Japan are the largest Free World producers of the element. 

Tellurium improves the machinability of copper and stainless steel, and its addition to lead decreases the corrosive action of sulfuric acid on lead and improves its strength and hardness. Tellurium is used as a basic ingredient in blasting caps, and is added to cast iron for chill control. Tellurium is used in ceramics. Bismuth telluride has been used in thermoelectric devices. 

Lead Telluride. Lead teUuride [1314-91 -6] PbTe, forms white cubic crystals, mol wt 334.79, sp gr 8.16, and has a hardness of 3 on the Mohs scale. It is very slightly soluble in water, melts at 917°C, and is prepared by melting lead and tellurium together. Lead teUuride has semiconductive and photoconductive properties. It is used in pyrometry, in heat-sensing instmments such as bolometers and infrared spectroscopes (see Infrared technology AND RAMAN SPECTROSCOPY), and in thermoelectric elements to convert heat directly to electricity (33,34,83). Lead teUuride is also used in catalysts for oxygen reduction in fuel ceUs (qv) (84), as cathodes in primary batteries with lithium anodes (85), in electrical contacts for vacuum switches (86), in lead-ion selective electrodes (87), in tunable lasers (qv) (88), and in thermistors (89). 

Mercury Telluride. Compounds of mercury with tellurium have gained importance as semiconductors with appHcations in infrared detection (9) and solar cells (10). The ratio of the components is varied, and other elements such as cadmium, zinc, and indium are added to modify the electronic characteristics. 

Dimethoxybiphenyl can also be prepared by simply refluxing bis(4-methoxyphenyl)tellurium dichloride with degassed commercial Raney nickel. The yields are, however, lower and less reproducible, and the product may contain some bis(4-methoxyphenyl) telluride. 

The polar tellurium(II)-nitrogen bond is readily susceptible to protolysis by weakly acidic reagents. Eor example, the reaction of [Te(NMe2)2]oo with two equivalents of Ph3CSH produces the monomeric thiolato derivative Te(SCPh3)2. Alkynyl tellurides may be prepared by the reaction of terminal acetylenes with arenetellurenamides (Eq. 10.13). ... 

Tellur-verbindung, /. tellurium compound, -vorlegierung,/. tellurium prealloy, -wasser-stoff, m. hydrogen telluride. -wasserstoff-sSure, /. hydrotelluric acid (hydrogen telluride). -wismut, n. bismuth telluride. 

Selenium and Tellerium Tantalum is attacked by selenium and tellurium vapours at temperatures higher than 80°C. Only slight attack is observed on the metal by liquid selenides and tellurides of ytirum, the rare earths, and uranium at temperatures of 1300 to 2100°C, and tantalum is considered to be a satisfactory material in which to handle these intermetallic compounds. 

A process for the gravimetric determination of mixtures of selenium and tellurium is also described. Selenium and tellurium occur in practice either as the impure elements or as selenides or tellurides. They may be brought into solution by mixing intimately with 2 parts of sodium carbonate and 1 part of potassium nitrate in a nickel crucible, covering with a layer of the mixture, and then heating gradually to fusion. The cold melt is extracted with water, and filtered. The elements are then determined in the filtrate. 

Fig. 3. Tellurium helices in copper telluride halides. (Redrawn from J. Fenner and H. Schulz, Acta Cryst. B35, 307 (1979), Fig. 2, p. 311.)...

All the dialkali monosulfides are soluble in water and give alkaline solutions. The tellurides are instantly decomposed by air. They are soluble in water, but the solutions are easily oxidized to red polytellurides. The alkali metal tellurides are strong reducing agents which reduce tellurites to metallic tellurium. 

---