Volume resistivity table

To learn more about the possible effects of ionic impurities on volume resistivity, we added known quantities of various impurities which are frequently present in polyvinyl chloride. Lead chloride is postulated as the end-product when lead compounds are used to stabilize polyvinyl chloride. Laurie and benzoic cids probably result from wasteful decomposition of the lauroyl and benzoyl peroxides used to initiate the polymerization reaction. Of these impurities, only benzoic acid had any noticeable effect on volume resistivity (Table III). 

Lead compounds are generally added to polyvinyl chloride in electrical formulations in order to stabilize them against thermal decomposition 7 p.h.r. of National Lead Tribase XL modified tribasic lead sulfate was used throughout the present study. Since the stabilizer itself is an ionic impurity, it is remarkable to note that it actually increases volume resistivity (Table IV). 

Migration of ions through the plasticizer is frequently considered to be a function of the mobility of the plasticizer itself (2,5). In many electrical applications, where fugitive monomeric plasticizers like DOP can cause damage, they can be replaced by non-fugitive polymeric plasticizers such as viscous liquid polyesters. Comparison of DOP vs. a typical polymeric plasticizer, Rohm Haas Paraplex 0-25 poly (propylene sebacate), showed no significant improvement in volume resistivity (Table VI), particularly when its lower plasticizing efficiency was considered. Thus plasticizer mobilitv alone does not help us explain volume resistivity (5). 

Table 10.8 shows electric strengths. Table 10.9 shows volume resistivities, Table 10.10 shows dielectric constants, and Table 10.11 shows dissipation factors for coatings using most of the available resins. Magnet wire insulation is an important use for organic coatings. National Electrical Manufacturer s Association (NEMA) standards and manufacturers trade names for various wire enamels are shown in Table 10.12. This information can be used to guide the selection of coatings. However, it is important to remember the aforementioned warnings about blends of various resins and the effects on performance properties.

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. 

Low—medium alloy steels contain elements such as Mo and Cr for hardenabiHty, and W and Mo for wear resistance (Table 4) (7,16,17) (see Steel). These alloy steels, however, lose their hardness rapidly when heated above 150—340°C (see Fig. 3). Furthermore, because of the low volume fraction of hard, refractory carbide phase present in these alloys, their abrasion resistance is limited. Hence, low—medium alloy steels are used in relatively inexpensive tools for certain low speed cutting appHcations where the heat generated is not high enough to reduce their hardness significantly. 

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. 

Incorporation of AlCacac) into the polyimide disappointingly shows no significant reduction in volume resistivity relative to the polymer alone. Replicate measurements (1.59 x 10 and 1.12 x 10 ° ohm-cm) on two independently cast films support this conclusion. Reorientation of the same film in the electrode assembly yielded identical results suggesting uniform behavior throughout the film containing Al(acac),. Similar results were obtained on NiCl bl O filled polyimides. (Table V)... 

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. 

Table 8.3 Volume Resistivity and Dielectric Constant Values of Polymeric Insulating Materials. ..185...

Nevertheless, it would seem reasonable that, in the absence of any liquid plasticizer medium at all, mobility of ionic impurities would be reduced to such a low level that volume resistivity would remain high. For example, it is well known that polyvinyl chloride can be blended with nitrile rubber, such as Goodrich Hycar 1032 butadiene/acrylonitrile copolymer, and such polyblends are quite soft and flexible without the use of any liquid plasticizer at all (Table VII). 

The effect of cryogenic temperatures on the volume resistivity and electrical strength of G-10CR and G-l ICR epoxy laminates was first reported by Kasen et al. [21], as summarized in Table 5. The electrical strength was found to be independent of both temperature and composite type. The effect of temperature on the volume resistivity was similar for the two composites, increasing 1.5 to 2 orders of magnitude on cooling from 295 to 4 K. 

TABLE 9.8 Volume Resistivities of Metals, Conductive Plastics, and Various Insulation Materials... 

The volume resistivity of polytetrafluoroethylene remains unchanged even after a prolonged soaking in water, because it does not absorb water. The surface arc-resistance of PTFE resins is high and is not affected by heat aging. They do not track or form a carbonized path when subjected to a surface arc in air [39]. The electrical properties of PTFE are summarized in Table 3.6. 

Addition of a filler such as AKO s an alternate method to reduce creep. As shown in Table 3 this filler also increases mechanical strength as well as lowering the coefficient of thermal expansion. The latter aspect can be an important consideration when trying to match material coefficients of expansion in an encapsulating situation. It should also be noted that volume resistivity measurements of unfilled material (see Table 3) indicate these formulations provide satisfactory electrical insulation for encapsulating purposes. 

The results of the specific volume resistivity measurements on PK terpolymer are listed in Table 9.12 and plotted as a function of the reciprocal, absolute temperature in Figure 9.19. The p-dc value of PK terpolymer decreases about five decades (from about 1E14 Ohm.m to 1E9 Ohm.m) due to the change in the amorphous phase from a glassy into a rubbery state. The measured resistivity level is too high to be responsible for the low frequency background losses as measured in the 0.1 kHz. curve of Figure 9.17. 

The nummerical results of these measurements are listed in Table 10.1. Figure 10.11 shows resistivity values plotted as a function of the anti-static additive concentration. The addition of this additive certainly works the surface resistivity decreases about four decades and the volume resistivity decreases about eight decades due to the addition of 4 %wt. of Neostatic HB155 anti-static additive. The shape of these curves indicates that addition of higher concentrations of this additive will be hardly effective. 

Table 21.13 Volume Resistivity of PP/Epoxy/CB (70/30/6) and PP/Epoxy/CB (40/60/4) Blends with Different Processing Sequences.

The volume resistivity of an unplastlclzed pottant material such as EVA is 10 ohm-cm. The module current leakage at 1.5 kV with EVA is an order of magnitude lower than with plasticized PVB at 25-30°C and there appears to be no rise in leakage at 50-60°C. (See Figure H and Table I.) Similarly, the current leakage of modules containing plasticized PVB can be blocked by the Insertion of an additional high volume resistivity layer such as polyethylene terephthalate film as discussed below, which is resistant to the solvation effect of dlester plasticizers. 

Electrical and Chemical. Oven aging at ISO C for 26 days had no effect on the electrical volume resistivities of either FVF or EVA films. Both maintained 10 J2-cm (see Table IV). The plFVB increased from 10 il-cm to 10 J2-cm in four days due to the evolution of plasticizer and absorbed water. Both plasticizer and absorbed water in plFVB cause its low initial volume resisitivity. Low volume resistivity material used in a photovoltaic panel can cause electrical current leakage (1.). BAgMMA decreased from 10 n-cm to 10 5 in 10 days. 

Table 2.3 Volume resistivity versus cure conditions for a silver-filled epoxy adhesive ...

Table 2.4 Volume resistivities for silver-filled epoxy adhesives (ohm-cm)...

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