Electrical impedance properties of zeolite-epoxy composites

The AC electrical properties of zeolite-epoxy composites have been studied as a function of grain size, temperature and frequency. Tests were conducted on epoxy composites containing 15 wt-% natural zeolite filler of grain size 63, 125 or 300 mm. The impedance, dielectric constant, dielectric loss, relaxation time and conductivity all showed frequency, temperature and zeolite grain size dependence. The dielectric constant and dielectric loss increased with decreasing zeolite grain size and decreased with increasing applied frequency according to the polarisation processes. The AC conductivity of the composites increased with increasing applied frequency and decreased with increasing grain size of the zeolite filler. The electrical conduction was also studied as a function of temperature for the 125 mm grain size composite. The dielectric constant, dielectric loss and AC conductivity increased with temperature, whereas the relaxation time and activation energy decreased. A statistical physical model is presented to explain the observed AC electrical properties as a function of grain size, and the electrical properties were explained on the basis of the grain boundary conductivity in addition to the electronic and ionic mobility in zeolite channels and impurities. The study concludes that the overall AC electrical behaviour is influenced by changing the measuring conditions.