Cadmium particle size

The photoelectrochemical properties of CdS nanoparticles formed in LB films of cadmium arachidate on ITO glass (indium tin oxide-coated glass) were investigated [188]. The CdS particles were formed by exposure to H2S gas, and then the cadmium arachidate structure was regenerated by exposing the gas-treated films with aqueous solutions of CdCL. Gassing/immersion cycling increased the particle size from 2.3 0.7 nm after one cycle to 9.8 2.4 nm after five cycles. The 9.8-nm particles showed UV-visible ab-... 

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],... 

Brus and co-workers produced nanoparticles of CdSe from the pyrolysis of the single-molecular cadmium selenate precursor [Cd(SePh)2].392 The similar metal(benzylthiolate) compounds [M(SCH2C6i Is)2] (M = Zn, Cd) were also used in the solid-state preparation of ZnS and CdS particles and produced mixtures of the hexagonal and cubic phases of the crystallites, with sizes of 5nm, on thermolysis between 200 °C and 400 °C under nitrogen.393 The bis(trialkylsilyl)chalco-genides [(Me3SiE)2Cd] (E = S, Se), prepared by heterocumulene metathesis as in Equation (11), were used to produce nanoparticles. If the reactions are carried out in TOPO, TOPO-passivated CdE nanoparticles can be obtained although there was little control over particle size 394... 

Fig. 17 Cadmium selenide QDs, dissolved in toluene, fluorescing brightly in the presence of a ultraviolet lamp, in three noticeably different colors (blue 481 nm, green 520 nm, and orange 612 nm). The blue QDs have the smallest particle size, the green dots are slightly larger, and the orange dots are the largest. (Adapted from http //www. amazingrust.com/ experiments/current proj ects / Misc.html)...

Borgmann, U. and K.M. Ralph. 1986. Effects of cadmium, 2,4-dichlorophenol, and pentachlorophenol on feeding, growth, and particle-size-conversion efficiency of white sucker larvae and young common shiners. Arch. Environ. Contam. Toxicol. 15 473-480. 

Toxicology. Cadmium oxide fume is a severe pulmonary irritant cadmium dust also is a pulmonary irritant, but it is less potent than cadmium fume because it has a larger particle size. Chronic exposure is associated with nephrotoxicity. Several inorganic cadmium compounds cause malignant tumors in animals. 

Inhalation exposure to high levels of cadmium fumes or dust is intensely irritating to respiratory tissue. Particle size appears to be a more important determinant of toxicity than... 

Cadmium oxide is prepared by the reaction of cadmium vapor with oxygen. The metal is first melted in a steel retort and transported into a heated chamber where it is vaporized. The vapor is reacted with air, and the cadmium oxide formed is collected in a bag house. The particle size of the product depends on the ratio of air to cadmium vapor. The oxide may be further purified and particles of uniform size may be obtained by calcination at low red heat. 

The finely divided cadmium may be stored for several months either as a slurry or in a dry state. (A dry 7 month-old sample was just as reactive as a fresh sample.) Strict anhydrous, airless conditions must be maintained, however. The cadmium crystallite sizes are variable but are generally in the 100-1000 A range. Particle sizes range up to several microns, with some particles even much larger. (Nontransition metals yield more nonuniform particle distributions than transition metals, which form stronger complexes with the solvent). 

Cadmium sulfide suspensions are characterized by an absorption spectrum in the visible range. In the case of small particles, a quantum size effect (28-37) is observed due to the perturbation of the electronic structure of the semiconductor with the change in the particle size. For the CdS semiconductor, as the diameter of the particles approaches the excitonic diameter, its electronic properties start to change (28,33,34). This gives a widening of the forbidden band and therefore a blue shift in the absorption threshold as the size decreases. This phenomenon occurs as the cristallite size is comparable or below the excitonic diameter of 50-60 A (34). In a first approximation, a simple electron hole in a box model can quantify this blue shift with the size variation (28,34,37). Thus the absorption threshold is directly related to the average size of the particles in solution. 

In the presence of an excess of sulfide ion, [Cd2+ /[S2-] = 5, and in the absence of any protecting agent such as HMP, the absorption threshold of the cadmium sulfide particles reaches that of the particles obtained in aqueous solution (41) (490 nm) and the presence of HMP makes it possible to obtain smaller particle sizes (absorption threshold of the order of 470 nm). 

The fluorescence of cadmium sulfide is strongly dependent on the particle size and the presence or absence of sulfide vacancies (57,58). The fluorescence of cadmium sulfide particles observed in solution in water (37,59,60) and in acetonitrile solution (59) is dependent on the particle method of preparation of CdS particles ... 

In the presence of an excess of sulfide ions two fluorescence emissions are observed. The first is centered at 450 nm and is attributed to the direct recombination of charge carriers. The second emission band, observed at around 650 nm, depends on the particle size. This second emission band is very weak and is very often quenched by the presence of species absorbed at the interface. By analogy it could be attributed to cadmium ion vacancies. 

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