Metals tellurium

Other Metals. Tellurium has been added to copper-base, lead-base, and tin-base bearing aUoys. In babbit-type aUoys, teUurium controls the stmcture and improves uniformity and fatigue resistance by restraining the tendency to segregation (see Bearing Materials). 

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. 

See Ammonium nitrate Metals Chlorine Metals Chlorine trifluoride Metals Copper(II) nitrate Tin Fluorine Metals Iodine bromide Metals Iodine heptafluoride Metals Potassium dioxide Metals Sodium peroxide Metals Sulfur Metals Tellurium Tin... 

Elemental composition H 1.56%, Te 98.44%. The gas is identified by its physical properties and measured by chemical analysis. Two most confirmatory methods recommended here are (1) GC/MS, the characteristic mass ions should be in the range 126 to 132, and (2) furnace-AA or ICP emission spectroscopic analysis for metalic tellurium. For the AA analysis, hydrogen telluride gas should be passed through water and the solution acidified and analyzed for tellurim. Hydrogen may be measured by the classical combustion method involving oxidation to form water, followed by gravimetry. 

Tellurium burns in air with a greenish-blue flame. The combustion product is dioxide, Te02, the most stable oxide of the metal. Tellurium also forms other oxides the monoxide, TeO, the trioxide, TeOs, and the pentoxide, Te205. Monoxide has not yet been obtained in solid form. Like sulfur and selenium, tellurium forms oxyacids. Such oxyacids include orthotelluric acid, HeTeOe and tellurous acid, H2Te03, in which the metal is in +6 and +4 valence states respectively. 

Tellurium is not an essential element, and tellurium compounds are in general more toxic than their selenium counterparts. Metallic tellurium is known to have a teratogenic effect in rats, though no studies have been done on the toxicity of tellurium donor compounds (35). 

Both alkyl and aryl tellurosilanes act as a good source of Rib and Te2 ligands, forming transition metal-tellurium clusters with cobalt(II) and copper(I) salts. The nuclearity of the cluster is determined primarily by the phosphine present, but also by... 

Selenium forms a volatile derivative, piazselenol, which can be subjected to GC analysis (Scheme 5.39). Young and Christian [612] treated selenium with 2,3-diaminonaph-thalene at pH 2.0 and extracted the resulting piazselenol into -hexane. With the use of an ECD, down to 5 10-I° g of selenium could be detected. The procedure, applied to the analysis of selenium in human blood, urine and river water, led to results equivalent to those obtained by neutron activation analysis. Similarly, Nakashima and Toei [613] performed the reaction of selenium (as selenious acid) with 4-chloro-o-phenylenediamine at pH 1 and extracted the derivative into toluene. They reported a detection limit of 0.04 jug. Shimoishi [614] analysed the content of selenium in metallic tellurium by this method. The sample was dissolved in aqua regia, followed by reaction with 4-nitro-o-phenylenediamine and extraction into toluene. Down to 10 ng of selenium could be determined using only a few milligrams of sample. Common ions did not interfere even when present in a large excess. Selenium in marine water was determined after the same derivatization step [615],... 

Ferric tellurite occurs in nature as the mineral durdenite in Honduras,4 associated with metallic tellurium. Hardness 2 to 2 5. Its chemical composition closely approaches that represented by the formula Fe2O3.3TeO2.4H2O, or Fe(Te03)3.4H20. Emmonsite is another naturally occurring ferric tellurite found in Colorado 5 as yellowish green scales, associated with lead carbonate and quartz. 

Electrodeposition of Main Group Elements and Transition Metals. The electrodeposition of tellurium, Te, has been investigated in an acidic EMlCl-ZnCl2 ionic liquid [84]. Tellurium tetrachloride, TeCLi, is soluble in the ionic liquid. The electrodeposition of metallic tellurium occurs at around 1 V vs. Zn/Zn(II). The formation of the Zn-Te alloys also occurs at more negative potentials. The further reduction of metallic tellurium to Te(—11) is reported as well just as in the chloroaluminate ionic liquid. 

Typical procedure. A mixture of di(p-methoxy)phenyltelluride (684 mg, 2 mmol) P(pyrro)3 (579 mg, 2.4 mmol) and Ni(PEt3)4 (106 mg, 0.2 mmol) in acetonitrile (5 ml.) was heated at 80°C overnight (20 h). The reaction mixture was poured into 10 mL of 1 M HCl to liberate metallic tellurium instantly. Extraction using CHjClj, drying over MgS04 and concentration afforded the crude product, which was subsequently passed through a short silica gel column (ethyl acetate/chloroform/hexane = 0.5 l 8) to give pure 4,4-methoxybiphenyl as a white solid (394 mg, 1.84 mmol, 92%). 

Metallurgy. — Metallic tellurium may be prepared from the precipitated tellurium dioxide by either the dry or the wet process. In the former the material is carefully dried, and... 

A variation of the above scheme gave tetrachlorotellurophene by heating for 40 hours at 250° a mixture of hexachloro- 1,3-butadiene and metallic tellurium.47... 

Technectium, properties of. See Transition metals Tellurium core radius, 362 elemental, 92f structure, 93... 

Ten /13-TePh ligands adopt an unsymmetrical pattern of one shorter , one longer and one intermediate Cu-Te bonding distances. These distances (2.552(3)-2.708(3) A) are, expectedly, shorter than their Ag-Te counterparts, and reflect the difference between the ionic radii of the two metals.This contraction of the metal-tellurium bonding distances is reflected in the overall size of the cluster frame. Thus, for comparison, the Te4 - Te7 distance is 12.29 A in 5 and 12.95 A in 3a similarly the telluride ligands Tel5-- Tel6 are 7.72 A apart in the copper complex whereas they are separated by 8.81 A in the silver cluster 3a. 

From evidence of diatomic selenium and tellurium in the vapor state and of octameric puckered rings in monoclinic selenium, as well as evidence of metallic tellurium at high pressure (23), it is suspected that in principle (if sluggish kinetics can be overcome) pressure and temperature may induce transformations in other group VI A elements comparable with those observed in sulfur. 

Deviations from the general trend exist within this group. Fibrous sulfur does not have the A8 structure of selenium and tellurium, and the helical sulfur molecule ( 83) is different from the helical selenium molecule ( Si). Also tellurium rings have not been observed, and metallic sulfur does not have properties similar to metallic tellurium or polonium. Thus, any generalized phase diagram will have serious limitations. 

Tellurium and compounds (as Te) Complaints of sleepiness, nausea, metallic taste, and garlicky odor on breath and perspiration associated with workplace exposures. Neuropathies have been noted in high-dose studies. Hydrogen telluride causes pulmonary irritation and hemolysis however, its ready decomposition reduces likelihood of a toxic exposure. Some tellurium compounds are fetotoxic or teratogenic in test animals. 0.1 mg/m (as Te) 25 mg/m (as Te) Metallic tellurium Is a solid with a sllveiy-whlte or grayish luster. 

The ability to control product formation, the reproducibility of results, and the relatively mild conditions under which the reactions proceed, have made cluster syntheses by this method very attractive. Furthermore, the starting materials are themselves readily prepared and easily stored and handled. This is especially valuable in metal telluride chemistry, in which suitable reagents for cluster syntheses are often unstable and must be generated in situ, leading to complex mixtures of reaction products. The use of the silylated tellurium reagents Te(TMS)2 and RTe-TMS has allowed access to a wealth of metal tellurium clusters with unique structures and properties. " ... 

Reactions.- Dehalogenatlon. Reductive dehalogenation of 1,2-dibromoalkanes has been reported using sodium telluride (prepared in situ from metallic tellurium and sodium formaldehydesulphoxylate... 

Tellurium exhibits a particularly complicated release behavior from overheated nuclear fuels. As a result, for a rather long time contradictory statements were made in this field. In the early years of nuclear technology, Parker and Lorenz (1963) reported on heating experiments of low-irradiated UO2 that under otherwise identical conditions tellurium release from Zircaloy-cladded fuel appeared to be lower by about a factor of 40 than from steel-cladded or non-cladded UO2. From this behavior they concluded that tellurium release from LWR fuel rods would not be identical to that from the UO2 fuel itself, but was controlled by some additional mechanism. In order to find out the reasons for these differences in behavior, the experimental results reported by different authors were systematically evaluated by Lorenz et al. (1983). It is well known from basic studies that metallic tellurium... 

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