Volume resistivities measurement

Surface and volume resistivity measurements have been performed on films of polymer alone and polymer with Al(acac) added. Special care was taken to insure that only films of uniformly high quality were measured. Regardless of the film pretreatment, volume resistivities on two independently cast films of polymer alone fall in the 10- - ohm-cm range. No previously published resistivity is available on this particular polymer although upon surveying several ether polyimides from independent sources we measured similar volume resistivities. 

Figure 13-1. Electrode systems, (a) Showing fringing effect and surface conduction in volume resistivity measurement (b) showing volume conduction in surface resistivity measurement (c) electrodes, guard ring and circuit for volume resistivity measurement (d) electrodes, guard plate and circuit for surface resistivity measurement. (G = glavanometer or other current measuring device.)...

Experimental determinations of resistivity have used several different arrangements of the electrical connections to the sample, variously termed electrodes, terminals or probes, as illustrated in Fig. 5.19. The simplest volume resistivity measurements use two electrodes, a 2-terminal method, in two basic arrangements. One is a rectangular or cylindrical block with electrodes on the ends, Fig. 5.19(a). The other is like that used for measurements of relative permittivity where electrodes are applied to either side of a thin disc, Fig. 5.20. The latter is more appropriate to high-resistivity materials. In both cases the volume resistivity is related to the measured resistance R between the electrodes by... 

Here we see that the resistance is independent of the electrode separation. The physical reason is that the major part of the voltage drop occurs in the immediate vicinities of the tips of the electrodes, and we may think of the resistance as the sum of a spreading resistance from the source electrode and a convergence resistance to the drain electrode. From this we conclude that 2-point probe measurements will not be very reliable or reproducible, because they will depend so sensitively on the small sample of material at the electrode tips. On a pliable material the form of indentation and contact area will be especially difficult to control with precision, and, in addition, we recognise that the material will be most distorted by the electrode pressure in just that region to which the resistance measurement is most sensitive. Therefore 2-point volume-resistivity measurements are not recommended. 

Fig. 5.22 Diagram of volume resistivity measurement with a 4-point probe.

Values of "dry" leakage currents for encapsulated samples which are presumed accurate and measure in the lOOpA-lnA range, should be easily verifiable by a volume resistivity measurement of the polymer, since the polymer s resistivity would have to be less than approximately lxlO1 ohms-cm. 

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 automated volume resistivity/dielectric properties measuring system is schematically drawn in Figure 5.2. The whole system is controlled by the HP9000/300 computer which runs either the specific volume resistivity measuring program or the dielectric properties measuring program. 

If the Ic-value after 60 seconds is used as I(dc) -value, for both experiments shown in the Figures 5.4 and 5.5, this l(dc) value contains a time dependent contribution i.e. it is too high. Thus, the calculated resistivity value will be lower than the real dc resistivity value. The results of all specific volume resistivity measurements (including the Ic[60 seconds] values) are plotted in Figure 5.6. The curves show that the difference between the I(dc)-data and the ic(60)-data is mainly present if the sample is in its glassy phase. For temperatures higher than 29°C the time dependent part of the charging current has vanished within 60 seconds i.e. Ic(60) and Idc are equal. 

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. 

In general, the instruments used for volume resistivity measurement will be satisfactory for surface resistivity. Charging current will rarely be a significant factor. 

Volume resistivity measurements have been reported on epoxy resin-polyaniline (PANI) blends resulting in the establishment of a correlation between a shoulder in... 

The most widely accepted test for determining conductivity of plastics is ASTM D257, which details procedures for measuring surface and volume resistivity. Where the intention is to find out dissipation of electrostatic charges, the more meaningful is surface resistivity. Volume resistivity measurements are useful in indicating the dispersion of a conductive additive throughout the matrix. 

The volume resistivity of a material is the ratio of the potential gradient parallel to the current in the material to the current density. Insulating materials are generally used to insulate and support components of an electric network from each other and from the ground. Therefore, it is desirable to have the insulation resistance as high as possible, consistent with acceptable mechanical, physical, chemical, and thermal properties. Volume resistivity measurements are designed to isolate the inherent properties responsible for the dc insulating qualities of a plastic material. Resistivities above 10 ohm cm are considered to be insulators those with values of 10 to 10 ohm cm are partial conductors. 

Fig. 9.5. Electrode arrangement for surface and volume resistivity measurement.

Surface and volume resistivity (measured by ASTM D257) of fluoropolymers is extremely high and they make good electrical insulation material. Neither properties are affected by time and temperature and are about 10 Q cm (volume resistivity) and 10 Q per square (surface resistivity). 

Volume resistivity measures the ability of a material to resist moving charge through its volume. The lower the volume resistivity of a material is, the more conductive the material. This test procedure is also described in detail in ASTM D257. 

Chomerics, Electrically Conductive Elastomers Volume Resistivity Measurement Procedures, (1995)... 

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