Sulfur formation

The formation of colloidal sulfur occurring in the aqueous, either alkaline or acidic, solutions comprises a serious drawback for the deposits quality. Saloniemi et al. [206] attempted to circumvent this problem and to avoid also the use of a lead substrate needed in the case of anodic formation, by devising a cyclic electrochemical technique including alternate cathodic and anodic reactions. Their method was based on fast cycling of the substrate (TO/glass) potential in an alkaline (pH 8.5) solution of sodium sulfide, Pb(II), and EDTA, between two values with a symmetric triangle wave shape. At cathodic potentials, Pb(EDTA)2 reduced to Pb, and at anodic potentials Pb reoxidized and reacted with sulfide instead of EDTA or hydroxide ions. Films electrodeposited in the optimized potential region were stoichiometric and with a random polycrystalline RS structure. The authors noticed that cyclic deposition also occurs from an acidic solution, but the problem of colloidal sulfur formation remains. 

The bromine water test is somewhat more satisfactory for pure tryptophane than the glyoxylic acid test. Hydrogen sulfide may interfere (owing to sulfur formation) and must be boiled out first. The solution to be tested must be acid with acetic acid. 

Formation Mechanisms. Sulfur Oxides, Module 6 Air Pollutants and Control Techniques, OL 2000 An Online Training Resource Basic Concepts in Environmental Science, North Carolina State University http //www.epin.ncsu.edu/apti/ ol 2000/module6/sulfur/formation/formfram1.htm... 

Potassium chlorate Sulfur Formation of explosive mixture sensitive to shock and friction... 

Increasing Vanadium and ADA Content. Raising the concentration of vanadium in the Stretford solution can increase the rate of elemental sulfur formation in the absorber/reactor, and thus lower the concentration of sulfur compounds that are converted to thiosulfate in the oxidizer (Moyes 1974 and Nicklin 1977). It may also be necessary to increase the ADA concentration as well, in order to convert the additional tetravalent vanadium that will be formed back into its pentavalent state. 

Due to the good nucleophilic nature of sulfur, formation of new C—S bonds is relatively easy. This property has been used for intramolecular peptide cyclization 1 and was exploited for preparation of methylenethio ether surrogates, t >[CH2—S], initially as peptide gap inhibitors for blocking collagenase action. 2 These surrogates were later converted into sulfoxide and sulfone derivatives. This expansion of amide replacements compelled a more generalized nomenclature system for pseudopeptides (amides with one or more amide bond surrogates) and led directly to the psi-bracket convention. 1 ... 

With respect to the overall mechanism, it is worthwhile to comment briefly on the APCI results of high elemental sulfur yields, even in the absence of air. The results suggest that the reaction responsible for the elemental sulfur formation under these conditions may be reaction (12). The main reason for this contention is the fact that transition metals and their sulfides are known to be very good catalysts for H2S decomposition (11,... 

Iron monosulfides comprise about 20% of the iron sulfide minerals in the noneuxinic sediment and about 50% in the euxinic sediment. Their greater preservation in the euxinic sediment, as in sediment from Walker Lake, is probably a result of insufficient elemental sulfur formation in this extremely reducing environment. Seasonally aerobic conditions at the sediment-water interface of the noneuxinic sediment would promote elemental sulfur formation from the oxidation of H2S that accumulates in pore water. 

The gas reacts with metals (As, Sb, Mg, Zn, Cd, Tl, Pb, Mn, Ni, Co, Ag, etc.) reductively to give metal sulfides and metal oxides, although secondary reactions often lead to sulfates or sulfur formation. 

Werne J. P., Lyons T. W., Hollander D. J., Formolo M. J., Formolo M. J., and Sinninghe Damste J. S. (2003) Reduced sulfur in euxinic sediments of the Cariaco Basin sulfur isotope constraints on organic sulfur formation. Chem. Geol. 195, 159-179. 

Hiroyoshi et al. (1997) monitored the oxygen consumption, sulfur formation, total iron, and Fe(II) concentrations at different pH levels during the oxidation of chalcopyrite. On the basis of the reaction products formed, it was concluded that ferrous ions catalyzed the oxidation by dissolved oxygen in acidic media ... 

The solubility of CaS04(s) is about 0.016 M at 25°C. According to the foregoing rough calculation, sulfur should form in the reduction of in saturated CaS04(s) only if the pH is somewhat below 7. There are some indications that this conclusion agrees with the condition of natural sulfur formation. Elemental sulfur may be formed, however, as a kinetic intermediate or as a metastable phase under many natural conditions. 

Sulfur formation along the coast of eastern India near the village of Kona (Masulipatam, Madras) was described by lya and Sreenivasayi (1944,1945). Clays in certain coastal areas of the Bay of Bengal may be flooded during monsoons for several months at a time so that they become logged with sea water halophilic sulfate-reducers develop abundantly in the lower black clays. Diffusing sulfide ions are oxidised near the surface and produce colloidal and crystalline sulfur to a depth of some 20 cm. 

Sokolova, G.A., 1962. Microbiological sulfur formation in Sulfur Lake. Mikrobiologiya, 31 324—327. 

Taylor, C.D. and Wirsen, C.O. (1997) Microbiology and ecology of filamentous sulfur formation. Science, 277, 1483-1485. 

If the kinetics are rapid enough, as experienced at high oxidation concentration and high temperature, surface polarization may occur sufficient to cause both CuS and sulfur to form. Sulfur formation occurs by the reaction... 

The data suggest that sulfur formation on the electrode surface inhibits further oxidation of sulfide or polysulfide because extensive oxidation is absent after the first anodic peak and a sharp second anodic peak is absent under conditions where the chemical reaction is slow such as lower temperatures and sulfide concentrations (see Figures 1, 3, and 5). However, under conditions conducive to Reaction 7, there is a significant increase in the extent of oxidation (see Figures 1 and 4, and Figures 5 and 6). These data suggest that the sulfur film can be removed by Reaction 7 to form hypersulfide and/or its dimer. With the film removed, the hypersulfide can be readily oxidized to sulfur. Thus, the chemical reaction appears to assist in the oxidation process. 

In phase 1, with the higher pH s used, the sulfur formed by Reaction 25 or 26 would be expected to react more readily to give thiosulfate by Reaction 28. Thus, sulfur formation is reduced or eliminated and a greater amount of thiosulfate is formed (12). Also in phase 1, with excess bisulfite, the polythionate chain is not built up as in Reaction 29, but rather tends to be degraded to trithionate and thiosulfate, Reactions 14 and 27. 

Effective Clusterization Temperature as Function of Centrifugal Factor mv /T. At a 0.1 atm pressure and high centrifugal factor of mv /T 1, the effective clusterization temperature in sulfur (formation of Se and Sg) is about 850 K. Using the condensation temperature of sulfur, 7) 550 K, at 0.1 atm, estimate the effective clusterization temperature of sulfur as a function of the centrifugal factor. 

One of the other early investigations came from Lianos and Thomas [346] who used AOT micelles in heptane for the synthesis. Two solutions, one containing cadmium perchlorate hexahydrate and another containing sodium sulfide nonahydrate, were prepared. Mixing of the two solutions in the reverse micelles produced small particles of CdS. The solutions were bubbled with nitrogen gas for deoxygenation and avoiding colloidal sulfur formation. The same authors used... 

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