Metal sulphides properties

Hydrogen sulphide oeeurs naturally, e.g. in natural gas and petroleum, voleanie gases, and from deeaying organie matter. It may be present near oil wells and where petroleum is proeessed. Commereially it is obtained as a by-produet from many ehemieal reaetions ineluding off-gas in the produetion of some synthetie polymers (e.g. rayon, nylon) from petroleum produets, and by the aetion of dilute mineral aeids on metal sulphides. Physieal properties are summarized in Table 9.14 and effeets of temperature on vapour pressure are shown in Figure 9.5. 

Hydrogen sulphide is used in the preparation of metal sulphides, oil additives etc., in the purification and separation of metals, as an analytical reagent and as raw material in organic synthesis. Physical properties are summarized in Table 8.11 and effects of temperature on vapour pressure are shown in Figure 8.4. 

A method [62] has been described for the determination of down to 2.5pg kg-1 alkylmercury compounds and inorganic mercury in river sediments. This method uses steam distillation to separate methylmercury in the distillate and inorganic mercury in the residue. The methylmercury is then determined by flameless atomic absorption spectrophotometry and the inorganic mercury by the same technique after wet digestion with nitric acid and potassium permanganate [63]. The well known adsorptive properties of clays for alkylmercury compounds does not cause a problem in the above method. The presence of humic acid in the sediment did not depress the recovery of alkylmercury compounds by more than 20%. In the presence of metallic sulphides in the sediment sample the recovery of alkylmercury compounds decreased when more than lmg of sulphur was present in the distillate. The addition of 4M hydrochloric acid, instead of 2M hydrochloric acid before distillation completely, eliminated this effect giving a recovery of 90-100%. 

Relations between the structure and properties have been investigated in a variety of solids such as metal oxides, chalcogenides, pnictides and halides. In addition to studying model systems for testing theoretical predictions, solid state chemists have been preparing new classes of solids as well as novel members of known types of solids. In this section, we have chosen three classes of solids, viz. metal oxides, metal sulphides and metal fluorides, to discuss structure-property relations we shall concentrate especially on their electrical and magnetic properties. 

Correlations between catalytic activity and a variety of bulk properties of semiconductors have been reported (i) the average band gap of III-V and II-VI semiconductors and activity towards hydrogenation of isopropanol (ii) enthalpy of oxides and their activity towards oxidation of propylene and (iii) number of d-electrons (and crystal field stabilization energy) or 3rf-metal oxides and their activity towards N2O decomposition. The last correlation, due to Dowden (1972), is important since it provides a connection between heterogeneous catalysis and coordination chemistry of transition-metal compounds. A correlation between the catalytic activity of transition-metal sulphides towards hydrodesulphurization of aromatic compounds and the position of the transition metal in the periodic table has been made by Whittingham ... 

With sulphur, arsenic forms three stable sulphides of composition As2S2, As2S3 and As2S5. The two latter possess acidic properties and with metallic sulphides form series of thio-salts, analogous to the arsenites and arsenates. Intermediate oxythio-salts are also known. 

CATALYTIC PROPERTIES OF TRANSITION METAL SULPHIDES FOR THE DEHYDROGENATION OF SULPHUR CONTAINING MOLECULES. 

The catalytic properties of unsupported transition metal sulphides have been examined for the reaction of dehydrogenation of tetrahydrothiophene. This study has shown that a selectivity higher than 90% for thiophene formation can be obtained for the most active catalysts, essentially the second row sulphide catalysts. The comparison between the catalytic activities in both dehydrogenation of tetrahydrothiophene and... 

A number of important structure types are found in transition-metal sulphides which have no counterparts among oxide structures, notably the various layer structures and the pyrites, marcasite, and NiAs structures. Further, many sulphides, particularly of the transition metals, behave like alloys, the resemblance being shown by their formulae (in which the elements do not exhibit their normal chemical valences, as in 0983, Pd4S, TiSa), their variable composition, and their physical properties-metallic lustre, reflectivity, and conductivity. The crystal structures of many transition-metal sulphides show that in addition to M-S bonds there are metal-metal bonds as, for example, in monosulphides with the NiAs structure (see later), in chromium sulphides, and in many sub-sulphides such as Hf2S,... 

We have noted one difference between complex oxides and sulphides, namely, the compounds of class (c) have no counterpart among oxy-compounds. A second difference is that sulphides other than those of the most electropositive elements show more resemblance to metals than do oxides. Metal-metal bonding occurs only rarely in simple oxides whereas it is more evident in many transition-metal sulphides. In many complex sulphides of class (c), as indeed in simple sulphides such as those of Cu, it is not possible to interpret the atomic arrangements and bond lengths in terms of normal valeilce states of the metals, suggesting a partial transition to metallic bonding, as is also indicated by the physical properties of many of these compounds. 

Sulphur (S, at. mass 32.06) occurs in the oxidation states -II (in sulphide), IV (in SO2 and sulphite), and VI (in H2SO4 and sulphate). Sulphur dissolves in certain organic solvents (e.g., CS2 and CeHe) when dissolved in an alkali metal sulphide solution, it yields yellow polysulphides (S + nS —> Sn+i j. When heated with an alkaline solution of sulphite, sulphur forms thiosulphate. Sulphide, sulphite, and thiosulphate are reducing agents. Persulphate has strongly oxidizing properties. Complexes are formed by sulphide e.g., with As, Sb, Mo), and also by thiosulphate [e.g., with Ag, Cu, and Fe(lII)]. The most stable sulphur species is sulphate, which forms sparingly soluble compounds, for example with Ba and Pb, and stable soluble complexes with Zr and Th. 

Metal sulphide semiconductors/polymer nanocomposites are considered to be highly functional materials with many applications, such as in photoluminescent, photoelectric and non-linear optical materials. The flexibility and processability of polymer matrices can provide good mechanical properties. 

Other Metal Sulphides. The equilibrium between stoicheiometric TaSj and a non-stoicheiometric phase Ta g4 has been established by measurement of the electrical properties of compositional isotherms with the vapour pressure of sulphur between 900 and 1200 °C. The rules governing the formation of stable structures in the series of compounds (ZnO, and chalcogenides... 

The concept was elaborated as the expansion of the theory of liquid semiconductors [30] applied to the problem of electrochemical decomposition of liquid chalcogen-ide compounds [26, 31]. In particular, basic components of namral metal ores, non-oxidised metal sulphides, exhibit the properties of PFC in the fused state. According to Velikanov, the PFC is an idealised complex ion-electron conductor where several electron transport mechanisms (ionic, semiconductor, metallic) of different physical nature contribute to the overall conductivity, and each of these contributions exhibits its own temperature dependency of the conductivity [26,31]. 

True nanotubes built from layered inorganic materials have extraordinary mechanical properties and are already used in many applications. Especially the transition-metal sulphides M0S2 and WS2 have been studied to a large extent, and their most prominent application is as lubricants. Some systems have been investigated with respect to their ability of hydrogen storage and battery applicability. The synthetic routes for these systems are already well established paths, e.g. via... 

Sulphur dioxide will normally oxidize metals at elevated temperatures, simultaneously forming metal sulphides and oxides. Liquid sulphm- dioxide is a relatively efficient solvent with some water-like properties. Polar inorganic compounds are usually insoluble or only sparingly soluble in liquid sulphur dioxide, whereas covalent inorganic and organic compoimds are often dissolved, mostly forming stable solutions. The fact that aromatic hydrocarbons will dissolve more readily than aliphatics in sulphur dioxide is exploited on an industrial scale for the extraction of aromatics from crude oil according to the Edeleanu process. 

Many metal sulphides, selenides and tellurides have been prepared either as powders or as thin films. Sulphides like CdS can be also formed in colloidal suspension, whose optical properties depend on their particle size. 

Mrowec S, lanowski 1, Similarities and differences in defect dependent properties of transition metal sulphides and oxides , in Johannesen O, Andersen A G, Selected Topics in High Temperature Chemistry, Amsterdam, Elsevier, 1989, p. 55. 

Grzesik Z, Mrowec S, Walec T, Dabek J, New microthermogravimetric apparatus. Kinetics of metal sulphidation and transport properties of transition metal sulphides , J Therm Anal Cal, 2000 59 985-997. 

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