Polysulfides melting

The process of sulfurization is usually carried out by a sulfur bake, in which the dry organic starting material is heated with sulfur between 160 and 320°C a polysulfide bake, which includes sodium sulfide a polysulfide melt, in which aqueous sodium polysulfide and the organic starting material are heated under reflux or under pressure in a closed vessel or a solvent melt, in which butanol, CeUosolve, or dioxitol are used alone or together with water. 

Polysulfide Melt. Cl Sulfur Black 1 [1326-82-5] (Cl 53185), derived from 2,4-dinitrophenol, is the most important dye in this group which also includes the indophenol-type intermediates. The latter are appHed in the stable leuco form. The derived dyes are usually confined to violet, blue, and green shades. Other members of this group are intermediates capable of forming quinoneimine (10) or phenazone stmctures (11) that produce red-brown or Bordeaux shades ... 

Liquids. Some Hquid dyes are made directly from the thionation melt by additions of caustic soda and sodium hydrosulfide. Hydrotropic substances are sometimes added, either at the initial thionation stage or after the polysulfide melt is finished in order to keep the reduced dye in solution. Pardy reduced Hquids are also available. They are usually more concentrated than fully reduced Hquids, thus saving packaging and transportation costs. However, they require a further addition of reducing agent to the dyebath in order to obtain full color value. On the other hand, fully reduced Hquids are... 

Polysulfides are the key reactants in the high-density sodium-sulfur and Hthium-sulfur batteries [4] which are based on the following reversible redox reaction taking place in the polysulfide melt ... 

The understanding of the reduction process of sulfur requires the identification of the reduced forms of sulfur, that is, polysulfides or S . The phase diagrams of M2S —Sg systems (where M is an alkali-metal cation) have been reviewed [23], as also the properties of polysulfide melts [24]. Many polysulfides have been characterized in the solid state by x-ray diffraction, infrared and Raman spectroscopy [25]. The identification of polysulfides in solution is often rather difficult. The reason is that the dissolution of a M2S polysulfide leads, for most of them, to a disproportionation process of the type ... 

Sulfur dyes are a special class of dyes with regard to both preparation and application, and knowledge of their chemical constitution [1], They are made by heating aromatic or heterocyclic compounds with sulfur or species that release sulfur. Sulfur dyes are classified by method of preparation as sulfur bake, polysulfide bake, and polysulfide melt dyes. Sulfur dyes are not well-defined chemical compounds but mixtures of structurally similar compounds, most of which contain various amounts of both heterocyclic and thiophenolic sulfur. 

The characteristic properties of Polysulfide Melt (Chinonimin-) Dyes can be expressed to a large extent in a simplified model (see Scheme 2.8, p. 83). 

This class of compounds also includes phcnazone, phenothiazone, and phe-noxazone derivatives (12), and so these polysulfide melt dyes are also referred to as quinoneimine or indophenol sulfur dyes. 

The structure 15 can thus be regarded as the prototype of the polysulfide-melt dyes (quinoneimine or indophenol sulfur dyes) (Scheme 2.8). 

Polysulfide melt dyes, which are applied chiefly with dithionite and commonly show a higher degree of fastness, are called sulfur vat dyes. They include such dyes as C.I. Vat Blue 43 and C.I. Sulphur Black 11. 

The polysulfide melt process yields mainly reddish brown, violet, blue, green, and black sulfur dyes, depending on the intermediate. 

Polysulfide Melt, Solvent Reflux, or Reflux Thionation... 

Tables 3.9 and 3.10 present some examples of the preparation of polysulfide-melt dyes.

With polysulfide melt dyes (i.e., quinoneimine sulfur dyes), the reducing agent can attack not only the disulfide groups but also the quinoneimine group (as in the case of vat dyes). Dispersible pigments are used particularly for pad dyeing. 

The leuco form is absorbed by the substrate and then oxidized to the insoluble dye. Since several mercapto groups are present per dye molecule, oxidation causes not only dimerization but also cross-linking of dye monomers . For polysulfide melt dyes, the quinonimine group is also involved in the reaction. This is apparent in the change in shade that occurs during reduction. 

The life-limiting increase of resistance and decrease of capacity of cycled cells is usually attributed to the deteriorating effects of corrosion of the positive current collector— the cell container in the case of sodium core cells or a rod in the case of sulfur core cells. Apart from consuming the active material, corrosion may lead to the deposition of poorly conductive layers at the current collector surface, thus interrupting the contact of the inert electrode fibers with the current collector. Corrosion products may also deposit and block both the solid electrolyte and the electrode surface. The thermodynamic instability of metals in polysulfide melts severely limits the choice of materials interfacing the sulfur electrode.A fully satisfactory solution has not yet been reported. 

Another, exploratory version of the Na-S system (aimed at present at stationary applications) is under development at Dow Chemical Company. It operates at 300°C and utilizes hollow sodium borate glass fibers as electrolyte in the form of thousands of thin hollow fibers sealed at one end and open at the other to a common reservoir of molten sodium. The fibers are wrapped in Mo-coated aluminum foil which serves as a positive electrode for the polysulfide melt, which fills the space between the fiber wall and the Al. 

The physical, chemical, and electrochemical properties of the sulfur-sodium polysulfide system influence many aspects of cell performance. For example, the 300°C operating temperature is dictated by the requirement that reaction products be liquid, and it is likewise this requirement which ultimately limits the extent of cell discharge. The phase behavior of sulfur-sodium polysulfide melts has been determined by both differen-... 

Other physical properties of the sulfur-polysulfide melt influence cell performance and have been studied. Density is perhaps foremost among these since density variation during discharge will dictate cathode void volume requirements. Furthermore since the sulfur-polysulfide melt is a two-phase system (see Figure 2) over much of the discharge range, density in conjunction with viscosity and surface tension establish the nature of the phase separation. Measurements of density (19, 23) demonstrate that the reaction proceeds at 360°C according to ... 

The sulfur-sodium polysulfide system has received the attention of electrochemists but few of the studies have been under conditions comparable to sodium-sulfur battery operating conditions. The thermodynamics of the system have been studied by means of open-circuit potentials (17,27), and dynamic measurements have been made in fused salts (28). The most pertinent studies are those of sulfur-polysulfide electrochemistry in the actual sulfur-polysulfide melts (24, 29, 35). The results of these studies seem to indicate that both the oxidation and reduction reactions are rapid, although the oxidation reaction is hindered by the formation of an insulating sulfur film. These studies also concluded that the electrode reaction sequences were quite complex because of the multitude of polysufide species. As the system becomes better characterized more quantitative descriptions are possible as evidenced by a recent work which modeled the resistive drop through an actual sulfur impregnated graphite electrode in order to correlate the spatial distribu-... 

It is not possible to review all the work concerning sulfur electrode reactions in molten salts but only to highlight the main features.Much of this work has been motivated by interests in high-temperature batteries and in the electrolytic recovery of metals from their sulfides. 8olvents such as LiCl-KCl and KCN8 have been employed, but many studies have concerned pure molten polysulfide melts (cf. the Na-8 battery). 

Thompson SD, Newman J (1989) Differential diffusion coefficients of sodium polysulfide melts. J Electrochem Soc 136(ll) 3362-3369... 

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