Dielectrics Chlorinated

Progressive chlorination of a hydrocarbon molecule yields a succession of Hquids and/or soHds of increasing nonflammability, density, and viscosity, as well as improved solubiUty for a large number of inorganic and organic materials. Other physical properties such as specific heat, dielectric constant, and water solubihty decrease with increasing chlorine content. 

Aryl and, more so, chlorine substituents on silicon enhance thermal stability of silacyclobutanes. The rate of the first-order thermal decomposition of silacyclobutanes varies inversely with the dielectric constant of the solvent used. Radical initiators have no effect on the thermal decomposition and a polar mechanism was suggested. Thermal polymerization of cyclo-[Ph2SiCH212 has been reported to occur at 180-200°C. The product was a crystalline white powder which was insoluble in benzene and other common organic solvents [19]. 

Poly (vinyl chloride) occurs as a colourless rigid material. It is having a high density and low softenting point. It is also having a higher dielectric constant and power factor. The high chlorine content of poly (vinyl chloride) makes it flame retardant polymers. 

PCBs are attractive for industrial applications because of their stability and dielectric properties [351-354]. Figure 1 shows the structure of the biphenyl molecule along with examples of chlorination that can occur at any of the positions on the rings. The physical and chemical properties of both isomers and mixtures used in industrial applications depend upon the degree and position of the chlorine atoms [355 -358]. There are 209 possible chlorobiphenyl isomers and Table 4 lists the number of isomers for various degrees of substitution. However, many of these isomers do not occur in significant amounts in commercial products, and isomers with four or five chlorine atoms on one ring but none on the other are not detectable in PCB mixtures [359-362]. 

Polychlorinated biphenyls (PCBs) were manufactured by catalytic chlorination of biphenyl to produce complex mixtures, each containing 60-90 different PCB molecular species or congeners (see Chaps. 1 and 4). In the United States, PCB mixtures were manufactured by Monsanto under the trade name Aroclor and were widely used as dielectric fluids in capacitors and transformers from 1929 to 1978. PCBs are widespread contaminants of aquatic sediments and continue to be a focus of environmental concern because they tend to accumulate in biota and are potentially toxic. The following sections show the most effective bioremediation techniques applied to various PCB contaminated environments ... 

Uses Dielectric liquids in fixed paper capacitors heat-transfer liquid widely used in transformers and utility transmission lines swelling agents for transmission seals ingredient in lubricants, oils, and greases plasticizers for cellulose products, vinyl, and chlorinated rubbers in polyvinyl acetate to improve fiber-tear properties. In fluorescent and high-intensity discharge ballasts manufactured prior to 1979 (U.S. EPA, 1998) and in electric motors (Monsanto, 1960). 

The polychlorinated biphenyls (PCBs, coplanar biphenyls) have been used in a large variety of applications as dielectric and heat transfer fluids, lubricating oils, plasticizers, wax extenders, and flame retardants. Their industrial use and manufacture in the USA were terminated by 1977. Unfortunately, PCBs persist in the environment. The products used commercially were actually mixtures of PCB isomers and homologs containing 12-68% chlorine. These chemicals are highly stable and highly lipophilic, poorly metabolized, and very resistant to environmental degradation they bioaccumulate in food chains. Food is the major source of PCB residues in humans. 

Physical Properties.—Sulphuryl chloride is a colourless, fuming liquid, with an extremely pungent odour. Z)2 = 1-6074 ->t " = l-4437. It boils at 69-1° C. at 760 mm. pressure, and freezes at —46° C.5 The vapour density is normal at first, but when the chloride is kept, even at 100° C., its vapour commences to dissociate into sulphur dioxide and chlorine. At 200° C. dissociation is almost complete.6 When dissolved in benzene the substance shows a molecular- weight corresponding with S02C12. At ordinary temperatures the specific heat is 0-233, the latent heat of evaporation 32-4 calories per gram, and the heat of formation from the elements approximately 89,540 calories per gram-molecule.7 The dielectric constant at 20° C. is 8-5. As a solvent, the ebullioscopic constant of sulphuryl chloride has been found to have... 

FLUOROCARBON. A number of organic compounds analogous to hydrocarbons, in which the hydrogen atoms have been replaced by fluorine. The term is loosely used to include fluorocarbons that contain chlorine these should property be called chlorofluorocarbons or fluorocarbon chlorides, since ii is these which arc though) to deplete the ozone layer or (he upper atmosphere. Fluorocarbons are chemically inert, nonflammable, and stable to heat up to 260-3l6°C. They are denser and more volatile lhan the corresponding hydrocarbons, and have low refractive indices, low-dielectric constants, low solubilities, low surface tensions, and viscosities comparable to hydrocarbons. Some arc compressed gases others are... 

FORMAMIDE. Form amide (meibanamide), HCONHi. is the lirsi member of the primary amide series and is the only one liquid at room temperature. II is hygroscopic and has a faint odor of ammonia. Formamide is a colorless to pale yellowish liquid, freely miscible with water, lower alcohols and glycols, and lower esters and acetone. It is virtually immiscible in almost all aliphatic and aromatic hydrocarbons, chlorinated hydrocarbons, and ethers. By virtue of its high dielectric constant, close to that of water and unusual for an organic compound, formamide has a high solvent capacity lor many heavy-metal salts and for salts of alkali and alkalinc-carth metals. It is an important solvent, in particular for resins and plasticizers. As a chemical intermediate, formamide is especially useful in the synthesis of heterocyclic compounds, pharmaceuticals, crop protection agents, pesticides, and for the manufacture of hydrocyanic acid. 

Liquid insulators are required for circuit breakers, transformers, and some cable applications. Natural hydrocarbon mineral oils are commonly-used, as well as chlorinated aromatic liquids (desirable because of nonflammability). For high-temperature situations, silicone fluids may be used. Permittivities range between 2 and 7. Insulating liquids function both as electrical insulators and heat-transfer media. See also Dielectric Theory. 

PCBs are industrial compounds used as industrial, dielectric and heat transfer fluids, organic solvents, flame retardants, plasticizers, sealant and surface coatings. They may also be released to the atmosphere by waste incineration (Fig. 3). The worldwide production of this compound has been 1.3 million tonnes, of which 97% in the northern hemisphere [23]. The amount of chlorine atoms in the biphenyl mixtures is related to the duration and temperature of the chlorination process. The commercial mixtures were distributed under names such as Aroclor (Monsanto, USA) or Clophen (Bayer, EU). The chlorine atoms can substitute the para, meta and/or ortho positions of the biphenyls. There are 209 possible congeners. PCBs can be divided into nine isomeric groups and one decachlorobiphenyl, all with an empirical formula of C Hjo-uCln (n = 1-10) (Fig. 4). 

Chlorobenzenes have been widely used as solvents and degreasing agents in pesticides, including dichlorodiphenyltrichloroethane (DDT), and in dielectric fluids as industrial precursors in the production of phenols and as dyestuff intermediates. Chlorobenzenes represent a unique class of compounds because their hydrophobicity increases with chlorine substitution,... 

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