Electrical properties of filled silicone rubber

Rubber materials for high-voltage outdoor applications have been studied. They were prepared as mixtures of silicone polymer with different concentrations of powdered aluminium trihydrate as a filler. The dielectric properties, chi*(omega) = chi' - i chi , were measured at different temperatures using a low-frequency dielectric spectroscopy technique. Without any filler a classical interfacial relaxation was pronounced with dominating direct-current (dc) conduction in the losses, chi . On increasing the concentration of filler, a low-frequency dispersion mechanism started to dominate: the relaxation behaviour. On adding the filler, the de conduction first decreased and then increased again after a certain concentration level was passed. This behaviour showed that the filler particles acted like scattering centres or traps for conduction when the concentration was low. As the concentration increased, the conductivity of the filler particles and of the interface (between the filler particles and the polymer matrix) started to dominate the conduction. Master curve shifts of the data showed an Arrhenius type of activation. The data were modelled by superposition of three different processes, Havriliak-Negami dipolar relaxation, de conduction and low-frequency dispersion (hopping conduction) contributions, using a nonlinear least-squares fitting method.