Sl. Wu et Ic. Tung, DIELECTRIC-RELAXATION AND ELECTRICAL-CONDUCTION AT LOW-FIELD OF MINERAL-FILLED EPOXY, Journal of Materials Science, 31(8), 1996, pp. 2177-2186
Dielectric properties and conduction of the epoxy and its composites w
ere measured over the temperature range -20 to 70 degrees C and the fr
equency range 10(-4)-10(-1) Hz. Dielectric properties were obtained by
performing Fourier transforms on the charging and discharging curves.
The resulting isothermal frequency spectra of dielectric constants an
d dielectric loss factors were analysed using the Cole-Cole law to obt
ain the activation energy for each material. The activation energies w
ere also obtained for isothermal d.c. current. Current density-electri
c field-temperature characteristics are obtained for field levels up t
o 60 kV cm(-1), with step excitation of the applied field and currents
recorded after a delay time of 10 min. Current density and electric f
ield were computed and plotted for constant temperature. The linear (o
hmic) curves were obtained for fields up to about 60 kV cm(-1) for tem
peratures up to about 20 degrees C. The non-linearity at the higher fi
elds and temperatures did not imply the occurrence of non-ionic conduc
tion. It has been demonstrated that both electric conduction and relax
ation behaviour were ionic and could be fit by the Nakajima model for
the unfilled epoxy and the Taylor model for the composites.