Thallium , colloidal

Colloids of more electronegative metals such as cadmium and thallium also act as catalysts for the reduction of water. In the colloidal solution of such a metal, an appreciable concentration of metal ions is present. The transferred electrons are first used to reduce the metal ions, thus bringing the Fermi potential of the colloidal particles to more negative values. After all the metal ions have been reduced, excess electrons are stored as in the case of silver. 

Violence of reaction depends on concentration of acid and scale and proportion of reactants. The following observations were made with additions to 2-3 drops of ca. 90% acid. Nickel powder, becomes violent mercury, colloidal silver and thallium powder readily cause explosions zinc powder causes a violent explosion immediately. Iron powder is ineffective alone, but a trace of manganese dioxide promotes deflagration. Barium peroxide, copper(I) oxide, impure chromium trioxide, iridium dioxide, lead dioxide, manganese dioxide and vanadium pentoxide all cause violent decomposition, sometimes accelerating to explosion. Lead(II) oxide, lead(II),(IV) oxide and sodium peroxide all cause an immediate violent explosion. 

Karski and co-workers found that thallium acts also as a promoter and prevents the poisoning of the palladium particle with oxygen. Indeed, a bimetallic system which contained 5 wt% of Th led to 100% selectivity to gluconic acid at 95% conversion [117]. On their side, Boimeman et al. reported that charcoal-supported Pd-Pt catalysts prepared from a colloidal solution of Pd-Pt/NOct4Cl exhibit a superior activity and selectivity than industrial heterogeneous Pd-Pt-based catalysts [118]. 

Aluminium and magnesium selenides are very similar light brown powders, unstable in air. Zinc and iron (ferrous) selenides are more stable in air, the zinc compound being citron-yellow and the iron compound black and metallic in appearance.8 The latter becomes brown in air owing to oxidation. Ferric selenide is difficult to obtain pure. Cadmium selenide, which is dark brown, is very stable in colour and is used as a pigment. With thallium, selenium is said to form three distinct compounds,9 but analyses of these compounds have led to discordant results. The selenides of aluminium, chromium and uranium cannot be prepared in the wet way. Nickel selenide, unlike the sulphide, shows no tendency to form a colloidal solution. 

Violence of reaction depends on concentration of acid and scale and proportion of reactants. The following observations were made with additions to 2—3 drops of ca. 90% acid. Nickel powder, becomes violent mercury, colloidal silver and thallium powder readily cause explosions zinc powder causes a violent explosion... 

Metals or Metal Oxides. Explosions result on contact with Ni powder, Hg, colloidal Ag, thallium powder, Zn powder, PbO, Pb304, and Na202 violent decomposition occurs with barium peroxide, CuO, impure Cr03, iridium dioxide, Pb02, Mn02, and V205 and with Fe powder contaminated with a trace of Mn02.3... 

Thallium dimethyl hydrosulphide,—When an excess of yellow ammonium sulphide is added to an ammoniacal solution of thallium dimethyl bromide, a white precipitate of the hydrosulphide separates. This is washed with hydrogen sulphide water to purify it, but it tends to form a colloidal solution, wliich is difficult to filter. Wffien dry it decomposes witli explosion on heating or in contact with fuming nitric acid. It dissoh cs in dilute nitric acid, with the separation of sulphur and in dilute siilplmrie or acetic acid, with the evolution of hydrogen sulplude. 

A somewhat different, but very interesting, study on the chemical properties of colloidal thallium(O) in aqueous solution has been reported recently by Ershov and Henglein 362). When a deaerated 0.1 mM TICIO4 aqueous solution was y-irradiated, its absorption spectrum changed as shown in Fig. 20. The solution contained also 0.1 M... 

Bidogho G, Gibson PN, O Gorman M, Robert KJ (1993) X-ray absorption spectroscopy investigation of surface redox transformations of thallium and chromium on colloidal mineral oxides. Geochim Cosmochim Acta 57 2389-2394... 

Lindau J, Komg H-J, Dorfler H-D (1983) Systematisierung der Tfeftemperaturmodifikationen homologer Thallium(I)-Salze aUphatischer Carbonsauren durdi ihre Mischbaikeitsbeziehungen. Colloid Polymer Sci. 261 236... 

As noted in the introduction, the small band gap azides of lead, silver, and thallium exhibit many similar properties which differentiate them from the large band gap azides. Barium azide may be an intermediate case since with irradiation it shows properties similar to both groups of materials. The small band gap azides in question detonate while barium azide deflagrates but will not sustain detonation. When the small band gap azides, barium azide, and silver and lead halides are exposed to radiation, decomposition appears to take place in both the metal and anion sublattices. Apparently, colloidal metal is formed from the metal sublattice [7,8,81-84] and, in addition, nitrogen [85,86] or halogen gas [87,88] is liberated from the anion sublattice. The relationship... 

The photolysis of pressed pellets of thallous azide was studied by Deb and Yoffe [239]. Decomposition led to the formation of a thin surface layer which was assumed to be thallium. No induction period in the rate was observed. The rate at constant temperature for the full output of mercury lamp was proportional to the light intensity. The activation energy for decomposition was found to be 0.33 eV (405 < X < 436 nm) or 0.14 eV (320 < X < 380 nm), with a quantum yield of 2 X 10" for X = 365 nm. Studies of the photo-induced colloidal bands in TIN3 are reviewed by Wiegand (see Section D). 

The results indicate that, on the basis of the ductile-brittle temperatures, lead azide should be most susceptible to the fracture method of initiation. The ductile-brittle temperatures of sodium azide and thallium azide are the same, implying similar shock sensitivities this is contrary to experience. (See, however, the discussion in Sections C.2.a and C.3.a of Chapter 5 relating to stability, in the energetic sense, against conversion to the end products colloidal metal and nitrogen gas. These bear on the magnitude of the exothermicity parameter Q appearing in the heat-transfer equation and can qualitatively explain the discrepancy. Sensitivity and stability are concepts not independently defined or operable). 

The photolytic method has, of course, a long and important history in the formation of photographic images from silver halide emulsions. Over the past twenty years, predominantly from the work of Henglein and of Belloni, a wide variety of colloidal metals has been prepared by this method encompassing both main group metals such as cadmium [87, 88], thallium [89, 90] and lead, [91] as well as other noble [92-98] and non-noble transition metals [99-101]. Radiolytic methods differ in the type of redudng spedes which is formed under irradiation, which is a function of solvent and any added solute. The radiolysis of aqueous solutions of metal ions produces solvated electrons which may either react with the dissolved... 

Organic free radical reactions are also catalyzed by metal colldds. For example, although 1-hydroxy-l-methyethyl, (CH3)2COH , radicals generated by the photolysis of 50-propanol/acetone mixtures are unreactive towards thallium(I) ions or methylene chloride in water, the presence of colloidal silver induces them to reduce T1 to colloidal thallium (a one electron process) and CH2O2 to CHQ3 and Q (a two electron process Eqn. 6.9). [273]... 

In this chapter, special attention is given to the use of radiation for the synthesis of colloidal nano-particles and for the investigation of their chemical and electronic properties. Radiolytic preparation under strictly anaerobic conditions has been shown to be an especially useful method, which allows one to control particle formation in a reproducible manner. Most studies in the literature are concerned with particles of the noble metals, i.e. of Au, Pt, Ag and Cu. The radiolysis method enables one to prepare also colloids of the more electronegative metals, such as of cadmium and thallium. In addition, this method has also been used to initiate chemical reactions on the surface of nanoparticles in a controlled manner. 

Abuin, E., Lissi, E. Thallium) l+)/sodium(l+) competitive binding at the surface of dodecyl sulfate, Biij 35 mixed micelles. J. Colloid Interface Sci. 1992,151(2), 594-597. 

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