Tellurium deposition

The work of Verbrugge and Tobias on CdTe [8] comprises a comprehensive source of information about the electrochemistry of the compound and its components. Deposition features are reviewed, and thermodynamic, transport, and kinetic parameters for cadmium and tellurium deposition are reported. 

Telluretted hydrogen is soluble in water to some extent, but in course of time the telluretted hydrogen is decomposed and tellurium deposited. 

CdTe was also obtained using rotating disc electrode the kinetics of tellurium deposition process on solid tellurium electrode was analyzed, and the kinetic parameters were calculated [205]. 

Madoz-Escande, C, Garcia-Sanchez. L.. Bonliomme, T., and Morello, M. (2005). Influence of rainfall characteristics on elimination of aerosols of cesium, strontium, barium and tellurium deposited on grassland. J. Environ. Radioact. 84, 1-20. 

In principle, tellurium deposition on stainless steel in the primary system would largely prevent this element from being released to the containment. However, tellurium vapor could react chemically with a variety of metallic aerosols to form tellurides in particular it has a high affinity for silver and cadmium, as well as for tin volatilized from the Zircaloy claddings. Thus, tellurium transport through the primary system would be primarily controlled by aerosol transport characteristics. Spence and Wright (1987) have calculated that inclusion of these processes of depo-... 

The radioactive tellurium isotopes decay to their isobaric iodine daughter products. This means that from each location where tellurium deposits have formed, radioactive iodine isotopes will be released to the steam flow. However, the magnitude of these iodine sources can be assumed to be small compared to the direct volatilization of iodine from the fuel. Thus, they can usually be ignored when evaluating iodine input into the containment, with the only exception possibly being the short-lived... 

The main differences between VICTORIA and RAFT predictions are attributable to [15] the Tellurium deposition profile. Neither VICTORIA nor VICTORIA contain a chemisorbtion model for tellurium spedes or SnTe, respectively. Further more the wall condensation is the dominant deposition mechanism according to RAFT and TRAPFRANCE, whereas VICTORIA predicts aerosol deposition as the main process. Hnally the bend retention models are different in VICTORIA and RAFT. 

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert siHca or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acryHc acid were prepared from bismuth, cobalt, kon, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic siHcic acids. Preferred second-stage catalysts generally are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity and productivity (39,45,46). 

Tellurium and many other impurities remain undissolved. The solution is filtered and cooled to reverse the reaction and to deposit soHd selenium. Oeselenized liquor is recycled to the dissolution step. 

N. D. Sindeeva, Mineralogy andTypes of Deposits of Selenium and Tellurium, Interscience Pubhshers, a division of John Wiley Sons, Inc., New York, 1964. 

Like selenium, tellurium minerals, although widely disseminated, do not form ore bodies. Hence, there are no deposits that can be mined for tellurium alone, and there are no formally stated reserves. Large resources however, are present in the base-metal sulfide deposits mined for copper, nickel, gold, silver, and lead, where the recovery of tellurium, like that of selenium, is incidental. 

Production and Economic Aspects. Thallium is obtained commercially as a by-product in the roasting of zinc, copper, and lead ores. The thallium is collected in the flue dust in the form of oxide or sulfate with other by-product metals, eg, cadmium, indium, germanium, selenium, and tellurium. The thallium content of the flue dust is low and further enrichment steps are required. If the thallium compounds present are soluble, ie, as oxides or sulfates, direct leaching with water or dilute acid separates them from the other insoluble metals. Otherwise, the thallium compound is solubilized with oxidizing roasts, by sulfatization, or by treatment with alkaU. The thallium precipitates from these solutions as thaUium(I) chloride [7791 -12-0]. Electrolysis of the thaUium(I) sulfate [7446-18-6] solution affords thallium metal in high purity (5,6). The sulfate solution must be acidified with sulfuric acid to avoid cathodic separation of zinc and anodic deposition of thaUium(III) oxide [1314-32-5]. The metal deposited on the cathode is removed, kneaded into lumps, and dried. It is then compressed into blocks, melted under hydrogen, and cast into sticks. 

Tellurium [13494-80-9] M 127.6, m 450 . Purified by zone refining and repeated sublimation to an impurity of less than 1 part in 10 (except for surface contamination by Te02). [Machol and Westrum J Am Chem Soc 80 2950 1958.] Tellurium is volatile at 500°/0.2mm. Also purified by electrode deposition [Mathers and Turner Trans Amer Electrochem Soc 54 293 1928]. 

Selenium was isolated some 35 y after tellurium and, since the new element resembled tellurium, it was named from the Greek askrivr], selene, the moon. The discovery was made in 1817 by the Swedish chemist J. J. Berzelius (discoverer of Si, Ce and Th) and J. G. Gahn (discoverer of Mn) they observed a reddish-brown deposit during the burning of sulfur obtained from Fahlun copper pyrites, and showed it to be volatile and readily reducible to the new element. 

Tellurium and cadmium Electrodeposition of Te has been reported [33] in basic chloroaluminates the element is formed from the [TeCl ] complex in one four-electron reduction step, furthermore, metallic Te can be reduced to Te species. Electrodeposition of the element on glassy carbon involves three-dimensional nucleation. A systematic study of the electrodeposition in different ionic liquids would be of interest because - as with InSb - a defined codeposition with cadmium could produce the direct semiconductor CdTe. Although this semiconductor can be deposited from aqueous solutions in a layer-by-layer process [34], variation of the temperature over a wide range would be interesting since the grain sizes and the kinetics of the reaction would be influenced. 

The solution should be free from the following, which either interfere or lead to an unsatisfactory deposit silver, mercury, bismuth, selenium, tellurium, arsenic, antimony, tin, molybdenum, gold and the platinum metals, thiocyanate, chloride, oxidising agents such as oxides of nitrogen, or excessive amounts of iron(III), nitrate or nitric acid. Chloride ion is avoided because Cu( I) is stabilised as a chloro-complex and remains in solution to be re-oxidised at the anode unless hydrazinium chloride is added as depolariser. 

Deslouis C, Maurin G, Pebere N, Tribollet B (1988) Investigation of tellurium electrocrystal-Uzation by EHD impedance technique. J Appl Electrochem 18 745-750 Yagi I, Nakabayashi S, Uosaki K (1998) In situ optical second harmonic rotational anisotropy measurements of an Au(l 11) electrode during electrochemical deposition of tellurium. J Phys Chem B 102 2677-2683... 

Gregory WB, Norton ML, Stickney JL (1990) Thin-layer electrochemical studies of the underpotential deposition of cadmium and tellurium on polycrystalline Au, Pt and Cu electrodes. J Electroanal Chem 293 85-101... 

Dennison S, Webster S (1992) An investigation into the effect of ionic species on the deposition of tellurium and the formation of cadmium telluride. J Electroanal Chem 333 287-298... 

The induced co-deposition concept has been successfully exemplified in the formation of metal selenides and tellurides (sulfur has a different behavior) by a chalcogen ion diffusion-limited process, carried out typically in acidic aqueous solutions of oxochalcogenide species containing quadrivalent selenium or tellurium and metal salts with the metal normally in its highest valence state. This is rather the earliest and most studied method for electrodeposition of compound semiconductors [1]. For MX deposition, a simple (4H-2)e reduction process may be considered to describe the overall reaction at the cathode, as for example in... 

Telluro-cyanide (presumably TeCN ) has been explored as a source of tellurium for electrodeposition of CdTe [14], on account of the possible advantage that this species is less likely than tellurium dioxide to oxidize the cathodically produced telluride ion. Bath solutions were prepared by dissolving powdered Te in a concentrated aqueous solution of KCN and adding CdCb and EDTA. Stoichiometric CdTe deposits, free of excess Te, were reported. 

Darkowski and Cocivera [94] investigated trialkyl- or triarylphosphine tellurides, as low-valent tellurium sources, soluble in organic solvents. They reported the cathodic electrodeposition of thin film CdTe on titanium from a propylene carbonate solution of tri-n-butylphosphine telluride and Cd(II) salt, at about 100 °C. Amorphous, smooth gray films were obtained with thicknesses up to 5.4 p,m. The Te/Cd atomic ratio was seen to depend on applied potential and solution composition with values ranging between 0.63 and 1.1. Polycrystalline, cubic CdTe was obtained upon annealing at 400 C. The as-deposited films could be either p- or n-type, and heat treatment converts p to n (type conversion cf. Sect. 3.3.2). 

The electrodeposition of tellurium and silver has been investigated in dilute aqueous solutions of tellurous acid and Ag " ions (concentrations in the order of 10 to 10 " M) in 0.1 M HCIO4 [164], In particular, cyclic voltammetry experiments were conducted with rotating glassy carbon disk electrodes in baths with various concentration ratios of Ag(I) and Te(IV) precursors, and their outcome was discussed in terms of the voltammetric features. For a Ag(I)/Te(IV) ratio close to 0.8, formation of quasi pure silver telluride, Ag2Te, was reported. The authors, based on their measurements and on account of thermodynamic predictions, assumed that silver is deposited first on the electrode (Ag" + e Ag), and then Te(IV) is reduced on the previous silver deposit with formation of Ag2Te according to the reaction... 

Cathodic deposition of bismuth(in) telluride films has been reported [224] also on copper and nickel foils, from aqueous nitric acid solutions of bismuth oxide and tellurium oxide in molar ratios of Bi Te = 3 3 and 4 3, at 298 K. The... 

Gerritsen HJ (1984) Electrochemical deposition of photosensitive CdTe and ZnTe on tellurium. J Electrochem Soc 131 136-140... 

Numerous works have been implemented on tellurium electrochemistry and its adsorption at metal surfaces. The morphological structures of electrodeposited Te layers at various stages of deposition (first UPD, second UPD, and bulk deposition) are now well known [88-93]. As discussed in the previous paragraphs, Stickney and co-workers have carried out detailed characterizations of the first Te monolayer on Au single-crystal surfaces in order to establish the method of electrochemical atomic layer epitaxy of CdTe. 

A similar procedure has been used to cathodically deposit lead telluride, PbTe, onto n-Si(lOO) wafers from an acidic electrolyte containing Pb(ll) and Te(IV) species at ambient conditions [106], Rock salt PbTe particles with size from 80 to 180 nm were obtained, distributed randomly on the Si substrate. The mechanism of PbTe nucleation was considered to involve OPD of 3D islands of tellurium followed by lead UPD. The barrier for anodic current formed at the n-Si/PbTe interface rendered the deposition of PbTe irreversible, although high-efficiency photooxidation... 

Gregory BW, Suggs DW, Stickney JL (1991) Conditions for the deposition of CdTe by electrochemical atomic layer epitaxy. J Electrochem Soc 138 1279-1284 Suggs DW, Stickney JL (1991) Characterization of atomic layers of tellurium electrodeposited on the low-index planes of gold. J Phys Chem 95 10056-64 Suggs DW, Stickney JL (1993) Studies of the structures formed by the alternated electrodeposition of atomic layers of Cd and Te on the low-index planes of Au. 1. LEED and Auger studies. Surf Sci 290 362-374... 

Yagi I, Lantz JM, Nakabayashi S, Corn RM, Uosaki K (1996) In situ optical second harmonic generation studies of electrochemical deposition of tellurium on polycrystalline gold electrodes. J Electroanal Chem 401 95-10... 

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