Selenium particles

Under the assumption that the gaseous sulfur, fine particle selenium and secondary fine particle sulfur measured at an ambient site originates from a single point source the tracer hybrid receptor model can be expressed in terms of the two equations... 

The color obtained is a function of both the composition and the particle size of the precipitated crystals. A redder color results from both increased selenium to sulfur ratio and from larger crystals, caused by a more severe heat treatment. Hence, it is possible to make, from the same glass, a series of color filter types, by controlled reheating. 

As discussed earlier the whole process is a redox reaction. Selenium is reduced using sodium borohydride to give selenide ions. In the above reaction, the metal ion reacts with the polymer (PVP or PVA) solution to form the polymer-metal ion solution. Addition of the selenide ion solution to the polymer-metal ion solutions resulted in instantaneous change in the colour of the solutions from colourless to orange (PVA) and orange red (PVP). This indicates the formation of CdSe nanoparticles. The addition of the selenide solution to the polymer - metal ion solution resulted in gradual release of selenide ion (Se -) upon hydrolytic decomposition in alkaline media (equation 4). The released selenide ions then react with metal ion to form seed particles (nucleation). 

We have reported a simple, green, bench top, economical and environmentally benign room temperature synthesis of MSe (M=Cd or Zn) nanoparticles using starch, PVA and PVP as passivating agents. The whole process is a redox reaction with selenium acting as the oxidant and MSe as the reduction product. An entire "green" chemistry was explored in this synthetic procedure and it is reproducible. The optical spectroscopy showed that all the particles are blue shifted from the bulk band gap clearly due to quantum confinement. Starch capped CdSe nanoparticles showed the presence of monodispersed spherical... 

Losi ME, WT Frankenberger (1997) Reduction of selenium oxyanions by Enterobacter cloacae SLDla-1 isolation and growth of the bacterium and its expulsion of selenium particles. Appl Environ Microbiol 63 3079-3084. 

Fine powdered cadmium reacts violently with selenium when it is heated. Nevertheless, the reaction is less violent than that of zinc with selenium. Therefore, one has to be careful when preparing cadmium selenide. The particle size of both reagents is a crucial safety factor regarding this reaction. 

Nickel and selenium interact with incandescence on gentle heating [1], as do also sodium and potassium, the latter mildly explosively [2], Uranium [3] and zinc [4] also incandesce when their mixtures with selenium are heated, and platinum sponge incandesces vividly [5], The particle size of cadmium and selenium must be below a critical size to prevent explosions during synthesis of cadmium selenide by heating the elements together. Similar considerations also apply to interaction of cadmium or zinc with sulfur, selenium or tellurium [6], Interaction of powdered tin and selenium at 350° C is extremely exothermic [7],... 

Antimony telluride films have been grown from antimony(III) and tellurium(IV) oxides.167 Antimony telluride films were stoichimetric and consisted of nanoscale particles of the size 100 nm. The films had a good crystallinity.167 Indium selenide films were grown from indium sulphate and selenium oxide precursors.168 The films consisted of large particles, 70 to 200 nm in diameter. The band gap was 1.73 eV.168... 

The bioavailability of selenium to a benthic deposit-feeding bivalve, Macoma balthica from particulate and dissolved phases was determined from AE data. The selenium concentration in the animals collected from San Francisco Bay was very close to that predicted by a model based on the laboratory AE studies of radiolabelled selenium from both particulate and solute sources. Uptake was found to be largely derived from particulate material [93]. The selenium occurs as selenite in the dissolved phase, and is taken up linearly with concentration. However, the particle-associated selenium as organoselenium and even elemental selenium is accumulated at much higher levels. The efficiency of uptake from the sediment of particulate radiolabelled selenium was 22%. This contrasts with an absorption efficiency of ca. 86% of organoselenium when this was fed as diatoms - the major food source of the clam. The experiments demonstrated the importance of particles in the uptake of pollutants and their transfer through the food web to molluscs, but the mode of assimilation was not discussed. 

Nanosized selenium particles were deposited onto Ti02 by the photocatalytic reduction of selenate (Se(VI) and selenite (Se(IV) ions) [317], The deposition of Se particles on TiOz was only observed in... 

Procedure. Transfer 5 g of air-dried soil, ground to pass a 2-mm mesh sieve, into a Kjeldahl flask and add four sodium sulphate tablets and one copper-selenium tablet. Add 25 ml sulphuric acid. Swirl the acid until no particles of the sample adhere to the bottom of the flask. 

In summary, coal-fired power plants appear not to be the major source of most enriched elements on particles In urban areas, despite the great attention devoted to mechanisms by which those elements become preferentially attached to fine particles (e.g.. Refs. 18, 34). However, the detailed studies of processes In coal-fired plants are of considerable value, as the fundamentals should be applicable to other kinds of combustion sources. Furthermore, It may be necessary to use this fundamental approach to develop methods for predicting the source compositions for coal-fired power plants that have not been measured. Selenium Is much... 

Other Sources of Selenium. In 1820 Leopold Gmelin prepared pure selenium from the fuming sulfuric acid of Graslitz [Kretzlitz] in Bohemia, and in the following year Buch and Wohler showed that this selenium came originally from the particles of iron pyrites dispersed in the alum shale from which the sulfuric acid had been prepared. 

Figure 8.2 depicts the principle of such an experiment. In air mass A below the cloud, there are sulfate and trace metals such as selenium in suspended particles, and S02 and oxidants in the gas phase. As the air... 

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