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Surface degradation and dielectric response of inorganic fillers in the polyethylene matrix

The dielectric properties of PE composite materials with various inorganic fillers (aluminum oxide, Al<sub>2</sub>O<sub>3</sub>; aluminum nitride, AlN, zirconium dioxide, ZrO<sub>2</sub>, titanium dioxide, TiO<sub>2</sub>, silicon dioxide, SiO<sub>2</sub> boron nitride, BN) were characterized at room temperature using dielectric spectroscopy in a wide range of frequencies (10<sup>-2</sup> Hz - 10 kHz). In few cases, we found a slight change of real permittivity (ε<sub>r</sub>) after addition of 20%vol of fillers. The permittivity values found for the different composite films investigated ranged from 2.4 to 22.5 (ε<sub>r</sub>) at 0.1 Hz, depending on the additive. The composites with TiO<sub>2</sub> and ZrO<sub>2</sub> additives were found to have the highest values of permittivity. Furthermore, at high frequencies, almost all composite films were found to reach a low dielectric constant (i.e. comparable to that of neat PE) whatever the permittivity value of the fillers. Surface erosion tests showed a good surface resistance to partial discharges when the filler permittivity was low.