Volume resistivity temperature

Electrical Properties. Polytetrafluoroethylene is an excellent electrical insulator because of its mechanical strength and chemical and thermal stabihty as well as excellent electrical properties (Table 6). It does not absorb water and volume resistivity remains unchanged even after prolonged soaking. The dielectric constant remains constant at 2.1 for a temperature range of —40 to 250°C and a frequency range of 5 Hz to 10 GHz. 

Electrica.1 Properties. Because of excellent electrical properties, FEP is a valuable and versatile electrical insulator. Within the recommended service temperature range, PTFE and EEP have identical properties as electrical insulators. Volume resistivity, which is >10 H/cm, remains unchanged even after prolonged soaking in water surface resistivity is >10 H/sq. 

Electrical and Mechanical Properties. Electrical properties include dielectric strength, dielectric constant, dissipation factor, and volume resistivity these properties can change with temperature and absorbed water. 

Poly(vinyl chloride) has a good resistance to hydrocarbons but some plasticisers, particularly the less polar ones such as dibutyl sebacate, are extracted by materials such as iso-octane. The polymer is also resistant to most aqueous solutions, including those of alkalis and dilute mineral acids. Below the second order transition temperature, poly(vinyl chloride) compounds are reasonably good electrical insulators over a wide range of frequencies but above the second order transition temperature their value as an insulator is limited to low-frequency applications. The more plasticiser present, the lower the volume resistivity. 

PTFE is an outstanding insulator over a wide range of temperature and frequency. The volume resistivity (100s value) exceeds lO Gm and it appears that any current measured is a polarisation current rather than a conduction current. The power factor is negligible in the temperature range -60°C to -i-250°C at frequencies up to lO" Flz. The polymer has a low dielectric constant similarly unaffected by frequency. The only effect of temperature is to alter the density which has been found to influence the dielectric constant according to the relationship... 

The nylons are reasonably good electrical insulators at low temperatures and under conditions of low humidity but the insulation properties deteriorate as humidity and temperature increase. The effects of the amount of absorbed water on the volume resistivity of nylon 66 is shown in Figure 18.15. This effect is even greater with nylon 6 but markedly less with nylon 11. Some typical electrical properties of the nylons are given in Table 18.5. 

The more the polysulphide the higher will be the dielectric constant and the lower the volume resistivity. There will be reduction in tensile strength and heat distortion temperature but an increase in flexibility and impact strength. 

Resin Material Compressive Modulus, psi x 103 Heat Distortion Temperature, °F, 264 psi Heat Resistance, Continuous °F Thermal Expansion, in./in.- C x 10-5 Thermal Conductivity, cal/cm2-sec-°C-cm x 10 4 Volume Resistivity, ohm-cm... 

FIGURE 19.6 Dependency on carbon black loading of perimeter distance between the nearest aggregates obtained from three-dimensional-transmission electron microscopic (3D-TEM) images (dp) and volume resistivity at room temperature (pv). (From Kohjiya, S., Kato, A., Suda, T., Shimanuki, J., and Ikeda, Y., Polymer, 47, 3298, 2006. With permission.)... 

The dielectric constant of a polymer (K) (which we also refer to as relative electric permittivity or electric inductive capacity) is a measure of its interaction with an electrical field in which it is placed. It is inversely related to volume resistivity. The dielectric constant depends strongly on the polarizability of molecules tvithin the polymer. In polymers with negligible dipole moments, the dielectric constant is low and it is essentially independent of temperature and the frequency of an alternating electric field. Polymers with polar constituents have higher dielectric constants. When we place such polymers in an electrical field, their dipoles attempt... 

For polyamine-cured resin, recycle of presoaked epoxy also increased both impact strength and heat deflection temperature. For polyamide-cured resin, recycle also increased volume resistivity. Pre-soaked recycle dramatically increased adhesion to aluminum, especially in the anhydride system. 

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