Insulators dielectric properties

Moisture and vapor penetration Condensation Electrical insulation Dielectric properties... 

Synthetic polymers are best known for their insulating dielectric properties which have been exploited for numerous applications in both the electrical and electronic industries. It was found recently that some polymers can also be rendered conductive by an appropriate treatment, thus opening the way to a new field of applications of these materials (2, 3). Usually, electrical conductivity is obtained by doping a neutral polymer, rich in unsaturation, with donor or acceptor molecules. These polymers are rather difficult to synthesize, which makes them very expensive besides they are often sensitive to environmental agents, like oxygen or humidity, thus restricting their practical use to oxygen-free systems. 

These postulated mechanisms3 are consistent with the observed temperature dependence of the insulator dielectric properties. Arrhenius relations characterizing activated processes often govern the temperature dependence of resistivity. This behavior is clearly distinct from that of conductors, whose resistivity increases with temperature. In short, polymer response to an external field comprises both dipolar and ionic contributions. Table 18.2 gives values of dielectric strength for selected materials. Polymers are considered to possess... 

Electrical Properties. Like unfluorinated siHcone counterparts, fluorosihcone elastomers have inherently good electrical insulating properties. The dielectric properties remain relatively unchanged when the elastomer is exposed to severe environments. 

Another important use of dielectrics is as intermetal dielectrics (IMDs), where the dielectrics insulate metal lines from each other. The dielectric material must fill small gaps with high aspect ratios (depth to width) while maintaining all other dielectric properties. It is essential that the IMDs are void-free at submicrometer dimensions for both performance and rehabiUty. 

Electrical Properties. AH polyolefins have low dielectric constants and can be used as insulators in particular, PMP has the lowest dielectric constant among all synthetic resins. As a result, PMP has excellent dielectric properties and alow dielectric loss factor, surpassing those of other polyolefin resins and polytetrafluoroethylene (Teflon). These properties remain nearly constant over a wide temperature range. The dielectric characteristics of poly(vinylcyclohexane) are especially attractive its dielectric loss remains constant between —180 and 160°C, which makes it a prospective high frequency dielectric material of high thermal stabiUty. 

The electrical-insulating and dielectric properties of the pure EPM/EPDM are excellent, but in compounds they are also strongly dependent on the proper choice of fillers. The electrical properties of vulcanizates are also good at high temperatures and after heat-aging. Because EPM/EPDM vulcanizates absorb Htde moisture, their good electrical properties suffer minimally when they are submerged in water. 

The dielectric properties of polar materials will depend on whether or not the dipoles are attached to the main chain. When they are, dipole polarisation will depend on segmental mobility and is thus low at temperatures below the glass transition temperatures. Such polymers are therefore better insulators below the glass temperature than above it. 

Low density polyethylene (LDPE). This is one of the most widely used plastics. It is characterised by a density in the range 918-935 kg/m and is very tough and flexible. Its major application is in packaging him although its outstanding dielectric properties means it is also widely used as an electrical insulator. Other applications include domestic ware, tubing, squeeze bottles and cold water tanks. 

Another example is the influence of the electrical resistance of PVC cable insulation. This is caused not by the organic pigment itself but by ethoxylated surfactants, which are added as auxiliaries in the manufacture of these pigments, especially azo pigments. Contrary to a repeatedly expressed view, a possible electrolyte content, which laked azo pigments for example can have, has no effect on the dielectric properties of PVC [34]. Some pigment manufacturers offer special product ranges with verified dielectric properties for this purpose. 

P.Y.17 may be used for mass coloration and also to print PVC film. For these purposes, P.Y.17 is frequently prepared on a VC/VAc (vinyl chloride/vinyl acetate) mixed polymer basis. Good dispersibility in plastics makes these preparations suitable even for thin films. The dielectrical properties of P.Y.17 allow its application in PVC cable insulations. 

P.R.41 is also known as pyrazolone red. It has lost most of its commercial importance in recent years. P.R.41 production is now limited to the USA, where it is mostly employed to lend color to rubber. To a lesser extent, P.R.41 is found in PVC excellent dielectrical properties make it a suitable candidate for PVC cable insulations. The pigment provides a medium to bluish red of limited brilliance, it is much bluer than P.R.38. P.R.41 is somewhat less fast than P.R.38, which is also true for its stability to a variety of organic solvents. However, it parallels P.R.38 in its alkali and acid resistance. P.R.41 is very lightfast in rubber 1% pigment concentrations equal step 6-7 on the Blue Scale, which meets practically any require-... 

P.R.lll is chemically related to the pyrazolone pigments P.O.34 and P.R.37. Its hue is somewhat bluer than that of its pyrazolone counterparts it equals that of Signal Red (RAL 3000). The lightfastness of P.R.lll is somewhere between that of P.O.34 and of P.R.37. P.R.lll performs similarly as far as other fastness properties are concerned. The pigment lends itself particularly to the coloration of rubber and PVC excellent dielectrical properties also render it suitable for cable insulations. Thermally, P.R.lll is not sufficiently stable to be used in polyolefins, styrene, ABS, and similar plastics. 

P.R.48 4 does not bloom in plasticized PVC and is almost completely fast to bleeding. Its tinctorial strength in this medium is equally good. Desirable dielectric properties make P.R.48 4 a suitable candidate for use in PVC cable insulations. The pigment is also used for mass colored secondary acetate threads, fibers, and films wherever it meets the requirements for application. 

P.R.57 1 is employed in cable insulations because of its good dielectrical properties. It is much more lightfast in rigid PVC transparent colorations (0.1% pigment) equal step 6 on the Blue Scale, while white reductions with TiOz match between step 4 and step 2, depending on the standard depth of shade and on the TiOz content. 

Good dielectrical properties make it a suitable candidate for PVC cable insulations. 

There are patents on the use of FCIO3 as a heat transfer medium in refrigeration (165) and as an insecticide-fungicide (123). Owing to its ability to absorb intensively slow electrons (138), FClOs can be used as a gaseous insulator. Its dielectric properties are superior to those of SFg, and it hardly deteriorates on exposure to y-irradiation (104). 

Many of the fundamental relationships and concepts governing the electrical properties of materials have been introduced in the previous section. In this section, we elaborate upon those topics that are more prevalent or technologically relevant in ceramics and glasses than in metals, such as electrical insulation and superconductivity, and introduce some topics that were omitted in Section 6.1.1, such as dielectric properties. 

In this section, we consider the insulating properties of polymers as dielectrics, and we also describe their electrical- and ion-conducting capabilities. Given the highly insu-lative nature of most polymers, we begin with dielectric properties and then describe special types of polymers that conduct either electrons or ions. 

See Dielectric Properties of Explosives Refs 1) Kirk 8c Othmer 5(1950), 51 75 (Dielectrics) 2) Kirk Othmer 11, 2nd edit(1966) pp 776ff (Insulation, Electric)... 

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