Thallium oxide deposition

Heating in the course of annealing precursors that were cathodically deposited on metal substrates can cause cracking of deposits [204] as a result of different thermal expansion coefficients. However, as a result of the high uniformity of component distribution, the time and, sometimes also, the temperature of the thermal treatment can be substantially reduced. The last factor is particularly essential for thallium systems because it allows one to carry out annealing without any additional sources of thallium oxide vapor [194,195,199]. 

It was found that at pH > 11 in the region of low anodic overpotentials the product of thallium oxidation on an inert substrate represents the individual phase of a mixed-valence oxide which was previously unknown [352,253]. On a copper substrate, this same phase can be formed simultaneously with thallium cuprate, while at the higher overpotentials the amounts of both products in the deposit prove to be small due to the preferential formation of TI2O3 which proceeds at a high rate. At anodic overpotentials that are not too high, the rations of the amount of thallium cuprate to that of the mixed oxide in the deposits grown on copper correlates with the rate of active dissolution of copper [354], i.e., cuprate is preferentially formed at the higher pH. 

Thallium oxide supported on differenf materials was studied as a catalyst in benzene acylation with In general, TIO deposited on... 

Craig and co-workers (17) have recently made a very thorough study of both the silver deposition and dissolution coulometers. They prefer the latter for very precise work and have used it to redetermine the electrochemical equivalent of silver and the faraday as 1.117972 0.000019 mg/coulomb and 96490.0 2.4 coulomb/g-equiv. (chemical scale), respectively. Foley (18) has suggested a silver and thallium oxide coulometer utilizing silver and thallium salts at pH 9.5 to give an overall cell reaction of... 

Thallium can be quantitatively separated by deposition as thallium oxide on a platinum anode at 0.70 V vs. normal hydrogen electrode from an ammoniacal sulphate electrolyte (224). The direct oxidation of thallium (I) to thallium (III) on a platinum anode at 1.34 V vs. SCE does not proceed with 100 per cent current efficiency in 1 M sulphuric acid. Ck)riou, Hure, and Meunier (225) showed that traces of thalUum deposited into a mercury cathode could be redissolved without oxidizing noticeable quantities of mercury. 

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. 

When burned in suitable pits, pyrite yields, among other products, sulfur dioxide, arseniouS and selenious adds, and the oxide of thallium, which are carried over into the first lead chamber, with the ferruginous dust. In this first chamber, espedally if it has no other communication with the following ones than the gas pipe, the oxide of thallium deposits and accumulates, and finally thallium sulfate, with sulfates of lead, iron, and other foreign substances coming fiom the pyrite. 

Not only compositions containing all the HTSC metal components, but also simpler subsets, may be considered as the precursors. Thus, by a combined technique [189], Ba-Ca-Cu films were obtained by electrodeposition and then thallium was introduced from the vapor phase in the course of simultaneous oxidation. In [190, 191], it was shown that reproducible preparation of Bi-Pb cuprates can be achieved when three-component precursors are deposited and the alkaline earth cations are then introduced before annealing. It is practically impossible to provide reproducible deposition of five-component precursors. Two-stage electrosynthesis of HBCCO [200] included the intermediate annealing of a Ba-Ca-Cu deposit followed by mercury electrodeposition on the resulting oxide substrate. 

Suspensions of HTSC for the electrophoretic deposition of bismuth [403-409] and thallium [403] HTSC, various cuprates of rare-earth metals and barium [204, 407,410-414], and also silver HTSC [415,416] and PbO-HTSC [417] compositions have been used. These are prepared in acetone, acetonitrile, toluene, butanol, methylethylketone, or mixed solvents. They contain chemically pure materials (silver is introduced as AgaO) dispersed thoroughly, first mechanically and then in liquid) by ultrasonic treatment (in which case the particles became charged). The choice of solvent is by and large determined by its effect on the stability of the deposited oxide [417]. 

Thallium diethyl carbonate.—When the corresponding bromide or iodide is boiled with silver oxide m aqueous solution, and the filtrate evaporated in the presence of air, the carbonate is deposited in glistening needles, which decompose at 20-t" C. The salt may be recrystallised from alcohol, or precipitated from alcoholic solution by ether, and it is less soluble in hot water than in cokL Its solutions show an alkaline reaction, and wdien treated with acids, salts are formed with the evolution of carbon dioxide. 

Thallium diphenyl acetate is obtained by treating the oxide with boiling glacial acetic acid, the evaporated solution depositing fine, transparent needles, M.pt. 262° C. The salt is completely soluble in hot pyridine, chloroform, toluene, ethyl acetate, or alcohol, moderately soluble in carbon tetrachloride or water, slightly soluble in ether or acetone, and insoluble in light petroleum. 

Aluminum is the commonest metallic element on Earth, occurring widely in aluminosilicate minerals and in deposits of the hydroxide bauxite. It is very electropositive and potentially very reactive, but forms a stable oxide film. Gallium, indium and thallium are rarer and less electropositive. 

It takes place at atmospheric pressure, between 450 and 550 C in the presence of a silver oxide based catalyst deposited on silica or of earth alkali metal oxides, thallium and lead, and with excess propylene. An inert (nitrogen, steam, etc.) is used as diluent, in order to absorb the heat generated daring the conversion, whose molar yield is 7Q per cent in relation to propylene. 

It is advisable to protect T1 from surface oxidation by coating it with a layer of paraffin or storing it under glycerol or petroleum. II. Brown and McGlynn report preparation of a good, smooth, cohesive electrolytic deposit of metallic T1 from a thallium perchlorate bath containing peptone as an anodic depolarizer and cresol as a further additive. Current densities of 0.5 to 1.8 amp./ 100 cm. are used. 

An alternative to cathodic deposition of the elemental metal is anodic deposition of a higher oxide (Table 2). For lead, thallium, manganese, and cobalt, this allows separation from the vast majority of metals. This concept can be extended to determination of bromide and chloride, as the respective insoluble silver halides. 

The chemical properties span a range similar to the representative elements in the first few rows of the periodic table. Francium and radium are certainly characteristic of alkah and alkaline earth elements. Both Fr and Ra have only one oxidation state in chemical comhina-tions and have little tendency to form complexes. Thallium in the 1+ oxidation state has alkah-like properties, but it does form complexes and has extensive chemistry in its 3+ state. Similarly, lead can have alkaline earth characteristics, hut differs from Ra in forming complexes and having a second, 4+, oxidation state. Bismuth and actinium form 3+ ions in solution and are similar to the lanthanides and heavy (Z > 94) actinides. Thorium also has a relatively simple chemistry, with similarities to zirconium and hafiuum. Protactinium is famous for difficult solution chemistry it tends to hydrolyze and deposit on surfaces unless stabilized (e.g., by > 6 M sulfuric acid). The chemistry of uranium as the uranyl ion is fairly simple, hut... 

Other superconducting materials deposited by the sol-gel process using metal alkoxide precursors are the 1,2,4 compound YBazCu408, bismuth strontium calcium copper oxides, bismuth lead strontium calcium copper oxide, and thallium... 

In addition to these direct NP oxidation detection experiments, the underpotential deposition (UPD) of metal ions from solution onto metal NPs during collisions between the NPs and an inert electrode was also reported (see Figure 8.18). Reactions for UPD of thallium and bulk electrodeposition of cadmium onto Ag NPs were used for detection, which formed bimetallic core-shell NPs (denoted Ag Tl and Ag Cd, respectively). For the case of thallium, it was shown that up to a... 

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