Electrical behaviour at high voltage on surface of SiC-β′-SiAlON ceramic composites

This study describes the electrical behaviour of SiC-β′-SiAlON particulate composite materials under pulsed high electric fields. If such composite materials present interesting mechanical and thermal behaviour at high temperature, they also display enhanced discharges on the surface when a high electric field is applied. The global electric field required for the discharge is much reduced compared to those for similar air gaps at the same atmosphere pressure. Furthermore, the electric field required for discharge varies weakly over a large range of the atmosphere pressure. Such composite materials can be used for electric devices, where a local high energy level at high temperature is necessary. It is shown that the electrical discharge proceeds in successive steps, the first one being the local ionisation of the air atmosphere. During this step, the mechanisms involved follows Paschen's law at the microscopic scale for gaps between conductive SiC grains, but also at the macroscopic scale for the electrode gap. When the air pressure increases, a departure from Paschen's law is observed and a mechanism of breakdown is proposed based on Fowler-Nordheim's law for field emission at thin SiC grain boundaries.