Flash sintering of alumina: Effect of different operating conditions on densification

Nearly pure α-alumina samples produced by uniaxial pressing were flash sintered under electrical fields ranging from 500 V/cm to 1500 V/cm in experiments at constant heating rate. Sintering temperature significantly decreased with the applied E-field even down to ≈900 °C at 1500 V/cm. The onset temperature for flash sintering can be successfully modelled as a function of the applied voltage. The sintering temperature is also shown to be strongly affected by the electrode materials used during the treatment: using silver or carbon electrodes the sintering temperature is about 300 °C lower than when using platinum electrodes. In addition, the bulk density and porosity of the sintered alumina ceramic correlate strongly with the imposed current limit. Power dissipation was analysed before and during flash sintering; the activation energy for conduction was calculated in both cases, indicating that the process is based on ionic diffusion phenomena. Finally, we showed that during flash sintering the activation energy for conduction decreases, suggesting the occurrence of physical or structural modifications induced by current localization at the grain boundaries.