Sintering of alumina in microwave-induced oxygen plasma

Small cylindrical tubes were sintered in a microwave-induced oxygen plasma, initiated and sustained inside a tunable, single-mode cavity. Temperature and shrinkage measurements of the specimens were achieved using an optical-fiber thermometer black-body sensor and a dilatometer, respectively. Sintering experiments at constant heating rate mere accomplished to obtain the activation energy for sintering of alumina in the plasma and in a conventional rapid-heating furnace. Diffusion of aluminum interstitials along grain boundaries was believed to be the dominant sintering mechanism, with an estimated activation energy of 488 +/- 20 kJ/mol for conventional sintering and an average activation energy of 468 +/- 20 kJ/mol for plasma sintering, A comparison of specimens sintered in the plasma to those sintered in a conventional furnace under the same temperature-time excursions and oxygen pressures showed an athermal effect due to the plasma, To further explore this athermal effect, sintering experiments in plasmas of different oxygen pressure mere conducted. The athermal effect was ascribed to an increase of aluminum interstitial concentration during plasma sintering, Sintering data were interpreted using the combined-stage sintering model.