Thallium oxide volatility

Crystal growth of these compounds is complicated by the high volatility of thallium oxides and thallium-containing compounds at elevated temperatures and the toxicity of thallium. Also, the similarity in structures leads to problems controlling phase purity and samples which appear to be single crystals based on their morphology can be shown to be complicated intergrowths by X-ray diffraction studies. 

Bluish white metal very soft and easily fusible density 11.85 mp 303.5°C (578°F) bp 1457°C (2654°F) volatilizes around 174°C (345°F) oxidizes in air, forming a coating of thallium oxide, TI2O reacts with sulfuric and nitric acids. 

Al, Ga, In and T1 differ sharply from boron. They have greater chemical reactivity at lower temperatures, well-defined cationic chemistry in aqueous solutions they do not form numerous volatile hydrides and cluster compounds as boron. Aluminium readily oxidizes in air, but bulk samples of the metal form a coherent protective oxide film preventing appreciable reaction aluminium dissolves in dilute mineral acids, but it is passivated by concentrated HN03. It reacts with aqueous NaOH, while gallium, indium and thallium dissolve in most acids. 

All metallic chlorides, except silver chloride and mercurous chloride, are soluble in H.O. but lead chloride, cuprous chloride and thallium chloride are only slightly soluble. Metallic chlorides when heated melt, and volaiilize or decompose, e.g.. sodium chloride, mp 804 (2 calcium, strontium, barium chloride volatilize at red heal magnesium chloride crystals yield magnesium oxide residue and hydrogen chloride cupric chloride yields cuprous chloride and chlorine. Sec also Chlorine Chlorinated Organics. Halides Hypochlorites and Sodium Chloride. 

Single-stage chemical synthesis by annealing stoichiometric mixtures of individual oxides is often used for preparing ceramics. When highly volatile oxides are used (thallium- and mercury-based HTSCs), the process is carried out in hermetically sealed ampoules with an excess of the volatile component. The heating temperatures usually exceed those of the crystallization and can take up to lOh or more. 

Many normal oxides are formed on burning the element in air or oxygen. This is true not only of the non-metals boron, carbon, sulphur and phosphorus, but also for the volatile zinc, cadmium, indium and thallium, the transition metals cobalt and iron, in finely divided condition, and the noble metals osmium, ruthenium and rhodium. With some elements, limiting the supply of oxygen produces the lower oxide (e,g, P40g in place of P4O40 (p. 332)). 

The metals of the aluminium sub-group are permanent in the air at ordinary temperatures, but when heated in oxygen or the air they become coated with their oxide. The volatility of the metals increases with the atomic weights, and the heavier metals are more easily reduced than those of lower atomic weight. The metals are all malleable, fusible, have small atomic volumes and form hydroxides, M(OH)3, which are typically amphoteric in the first three elements of the sub-group and basic only in the case of thallium. The last four members of the family form alums, and both aluminium and thallium form organo-metallic compounds, resembling zinc in this respect. 

Thallium Is moderately volatile In elemental form, as well as in halide, oxide or nitrate forms. Inorganic compounds of Tl(lll) thermally decompose to yield the respective Tl(l)-compounds, and the organic ones pyrolyze to Tl° or TI2O (see Table 1). 

When heating the samples, the volatility of Tl-compounds has to be taken into consideration. Either oxygen or hydrogen, respectively hydrogen diluted with nitrogen, can be used as carrier gas. The volatility in oxide, chloride or elemental forms leads to evaporation of Tl and some other trace elements selectively from the solid sample, which has to be considered also in technical processing of thallium-containing ores and other materials. 

These tests showed that thallium is also unsuitable for this reaction because the reduced form of the oxide is lost from the reactor due to its volatility. Hence, only the highly selective mdium(i)/mdium(iii) oxide remained as the catalyst of choice. 

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