Dielectric loss tangent maximum

Direct differentiation on the contribution of the Debye or the Wagner-Maxwell polarization to the ER effect was carried out by Hao [35]. The strategy employed in Hao s paper is to compare the temperature dependence difference of the dielectric loss tangent maximum values of commonly encountered thrcc-lypc polarizations, the ionic polarization, the Debye polarization, and the interfacial polarization. As shown in Eq.(147) in Chapter 7, for the Maxwell-Wagner polarization (also called the interfacial polarization) the dielectric loss tangent can be expressed as follows if the particle conductivity Op is much larger than that of the medium... 

An analysis of the dielectric data similar to that for the dynamic mechanical data was undertaken. The natural logarithm of the time to peak maximum vs. 1/T was plotted for the two peak maxima observed in the dielectric loss tangent as shown in Figure 11. The activation energies derived from linear least squares fit of the data in these plots are listed in Table II. 

Table 5.1 The dielectric loss/tangent delta maximum...

Figure 8.13 Mechanical and dielectric loss tangent tan 8 and NMR absorption line width (maximum slope, in gauss) of polytrifluorochloroethylene (Kel-F) (41).

The relaxation time i can be correlated with the dielectric dispersion peak frequency, fmax, at which the dielectric loss tangent shows a maximum value,... 

The maximum value of the dielectric loss tangent, tgt%, polarization can be expressed ... 

In conclusion, from a basic fact that the entropy of ER fluids. should greatly reduce after an electric field is applied, it is theoretically demonstrated that the maximum value of dielectric loss tangent of the dispersed particle should be larger than 0.1, which agrees well with the... 

As illustrated in Appendix 1 it can be proved that the relaxation time T2 corresponds to the frequency of the maximum in dielectric loss tangent (tan ). In this method the characteristic time constant T2 was chosen from the frequency at the maximum in tan( ). Hence, by using the relation T2 = T -JS equation (20) can be modified to... 

Fig. 6 shows a typical example for dielectric loss tangent, tan, curve according to equation (36). The measured data for dielectric loss tangent can be fitted to equation (36) in order to estimate values for S and T2. In addition, to estimate S and T2 the coordinates at the peak value (maximum) in tan can also be used ( see Fig 6). The T2 can be calculated using the frequency corresponding to the maximum in tan and S can be estimated using the peak value of tan as described in Appendix 1. 

Fig. 16 shows the dielectric loss tangent, tas (j), as a function of frequency for PYR14TSFI, at different temperatures. In order to estimate T2 and 5 these tan plots can also be used. Curve fitting to equation (39) or coordinates of the maximum in tan(j) can be used to determine T2 and 8. 

In addition to high breakdown strength, the electrical insulators for superconducting magnets must have excellent dielectric properties at cryogenic temperatures. Chant reported the results of measurements on dielectric constant and loss tangent (tan 5) for several polymers over the temperature range from 4.2 to 300 K [83], The variation of dielectric constant of samples as a function of temperature is shown in Fig. 15. The dielectric constants of nonpolar polymers, such as polyethylene, polypropylene and polytetrafluoroethylene, are substantially independent of temperature, whereas those of polar polymers except polyimide decrease by a maximum of 20% as the temperature is reduced. The values of tan 8 at the frequency of 75 cps for nonpolar polymers decreased by... 

Research of influence of introduction of hexsaazocyclanes on a microstructure of polyethylene terephthalate is carried out. The increase in ability modified PETP to crystallization, in comparison with not modified PETP, as hexsaazocyclanes play a role of the original centers of crystallization is revealed. Research plasticization effect of hexsaazocyclanes on polyethylene terephthalate is carried out. It is revealed, hexsaazocyclanes introduction influences a maximum of a tangent of dielectric losses polyethylene terephthalate, displacing it aside smaller temperatures. 

For initial polyethylene terephthalate the maximum of a tangent of dielectric losses (tg 8), corresponding depolsegmentation mobility, is observed at 115° C. 

For initial PETP maximum of tangent of dielectric losses (tg 8), corresponding to dipole segmental mobility, is observed at 115°C. Position of this maximum on temperature axis during introduction of 0,1% of hexaazocyclane, does not change, and by absolute value it decreases by 1,5 times. Further growth of modifier concentration by 1-3% causes sharp... 

The dielectric loss data calculated from the I(discharge) currents according to equation 5.19 show a clear maximum due to the glass-rubber transition for the experiments at 29°C and 20°C. These data are plotted in Figure 5.7 as a function of the frequency together with the AC data. The results of both measuring systems can be fitted reasonably. The measured dielectric loss and tangent delta maximum temperatures are... 

This equilibrated frequency point is well determined by the loss tangent, tan, or dielectric loss, which predicts the ability of the material to convert the incoming energy into heat. For example, for water, the maximum value for the dielectric loss is around 2.0 GHz, which lies in the range of domestic microwave ovens. 

Figures 1 and 2 respectively show the temperature dependence of the relative permittivity and loss tangent of relaxor ferroelectric PLZT (9.5/65/35). As the temperature increases from -60°C to 100°C, the relative permittivity generally increased due to the unfreezing of domains. Between 0°C and 10°C, a broad peak can be seen in the lower frequency curves. This peak corresponds to the diffuse phase transition in this relaxor ceramic from the ferroelectric to the paraelectric state (also called the relaxor phase). Further heating continued to increase the relative dielectric permittivity until a maximum was achieved, at which point, the crystal s structure became cubic. This maximum in the permittivity, which is frequency dependent, occurs at the Curie temperature. Evidence of these phase transitions can also be seen in the loss tangent graph in figure 2.

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