Volume resistivities values

Electrostatic spraying is based on the fact that most plastic powders are insulators with relatively high volume resistivity values. They accept a charge (positive or negative polarity) and are attracted to a grounded or oppositely charged object (that is the one being coated). 

Electrical Properties. The electrical properties of silicone gels are essentially the same as those of most clean, unfilled silicone elastomers and fluids. Typical values for dielectric constant and dissipation factor when tested at 25°C and 100 Hz are 2.7 to 2.9 and 0.001 to 0.002 respectively. Volume resistivity values, usually, fall in the 10 ohm- centimeter range. 

The Ki-value determination of PVC cable compounds The specific volume resistivity is the most important electrical property of an electrical grade PVC. It is measured on a heavily plasticised product, the cable compound, pressed to a 2 mm. thick sample sheet. Cable manufactures usually test the resistivity of these compounds on cable samples and express the results in a so-called Ki-value. The Ki-value is in fact a volume resistivity value (see below) but measured on a cable sample with tapwater as low potential measuring electrode. A series of Ki-value determinations was performed to investigate the different parameters influencing this quantity. 

I = measured current, Ampere A = electrode area, m2 d = electrode distance, m p = a specific volume resistivity value, Ohm.m... 

The results of the electrical resistivity and the agglomerate area ratio as a function of SME for polyamide 6 composites filled with 5 wt% Nanocyl NC7000 prepared under different melt mixing conditions are summarized in Figure 7.8. To vary the SME, different rotation speeds and mixing times were used. The lowest volume resistivity value was found at 2000 Q cm for the composites mixed at 50 rpm and 15 min corresponding to a SME of 0.5 kW h kg ... 

Volume resistivity is the ratio of the DC potential applied to electrodes embedded in a material to the current between them, typically expressed in megohm-centimeters. The measured current flows between electrodes 1 and 3, while stray current flows between electrodes 2 and 3, as shown in Fig. 8.15. Table 8.8 shows the volume resistivity values of some common fiberglass-reinforced material types. 

Table 1 lists the volume resistivity values measured for some metals, eutectic solders, electrically conductive adhesives, oxide-filled resins, and unfilled polymers. 

High-volume resistivity materials are desirable in applications requiring superior insulating characteristics. Table 4-3 lists typical volume resistivity values of some common plastics. 

Most elastomers do not conduct electricity or static well. In contrast, ECO and GECO elastomers characteristically have volume resistivity values as low as... 

Including a conductive carbon black, N472, in a CO compound can give volume resistivity values in the conductive range, as low as 1.6 X 10 ohm-cm, as shown in Figure 7.10. 

A linear relationship exists between the cohesive energy density of an abrasive (10) and the WoodeU wear resistance values occurring between comndum H = 9) and diamond H = 42.5). The cohesive energy density is a measure of the lattice energy per unit volume. 

Electromagnetic interference (EMI) testing has become more prevalent for materials that either emit or are affected by EMI. Shielding efficiency (SE) of materials is deterrnined by measuring electric field strength between a transmitter and receiver with or without the presence of the material under test. Several researchers have suggested a correlation between volume resistivity and SE values (300,301). 

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 apparent volume resistivity is dependent on the polarisation time (Figure 15.10). The initial polarisation current is effective for some time and if only a short time is allowed before taking measurements low values for volume resistivity will be obtained. 

The membranes also have a certain, though small ionic conductivity. The electrical resistance of membranes when referred to unit surface area is 10 to 10 Q-cm, which when allowing for the small membrane thickness (about 10 nm) corresponds to the rather high value of specific (volume) resistance of 10 to 10 Q-cm. 

For mixed solvents the volume average value for the product is used [248]. Typical values for low molecular weight solutes fall in the range 0.5-3.5 x 10 m /s. The higher value is typical of organic solvents of low viscosity such as hexane, and the lower value for polar aqueous solvents. The column flow resistance... 

The bulk (or volume)-specific resistance is one of the most useful general electrical properties. Specific resistance is a physical quantity that may vary more than 10 in readily available materials. This unusually wide range of conductivity allows wide variety of electrical applications. Conductive materials, such as copper, have specific resistance values of about 10 fl-cm, whereas good insulators such as polytetrafluoroethylene and LDPE have values of about 10 fl-cm. Specific resistance is calculated from the following equation where R is the resistance in ohms, a is the pellet area in square centimeters, t is the pellet thickness in centimeter, and P is the specific resistance in ohm-centimeter ... 

In contrast to metals and semiconductors, the valence electrons in polymers are localized in covalent bonds.The small current that flows through polymers upon the application of an electric field arises mainly from structural defects and impurities. Additives, such as fillers, antioxidants, plasticizers, and processing aids of flame retardants, cause an increase of charge carriers, which results in a decrease of their volume resistivity. In radiation cross-linking electrons may produce radiation defects in the material the higher the absorbed dose, the greater the number of defects. As a result, the resistivity of a radiation cross-linked polymer may decrease. Volume resistivities and dielectric constants of some polymers used as insulations are in Table 8.3. It can be seen that the values of dielectric constants of cross-linked polymers are slightly lower than those of polymers not cross-linked. 

Volume Resistivity and Dielectric Constant Values of Polymeric insulating Materials... 

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