| Small cylindrical tubes made from alumina and alumina doped with magnesia were sintered in a microwave induced oxygen plasma, initiated and sustained inside a tunable single mode (TM;A comparison of specimens sintered in the plasma to those in the conventional furnace under the same temperature-time excursions and oxygen pressures shows an athermal effect due to the plasma. To further explore this athermal effect, sintering experiments in plasmas of different oxygen pressures were conducted. Sintering data were interpreted using the combined stage sintering model. The athermal effect was ascribed to an increase of aluminum interstitial concentration during plasma sintering. It is proposed that the energy required for the creation of point defects in plasma sintering was likely contributed from the recombination reactions of electrons and oxygen ions on the particle surfaces.;One of the ultimate objectives for sintering studies is to be able to predict densification results under different thermal histories for a given processing method. Based on the combined stage sintering model, a new concept of the master sintering curve was developed, which characterizes the sintering behavior for a given powder, green density, and green body process regardless of the heating profiles. This concept was applied to various powder systems (ceramics, metals, and composites) to demonstrate its validity. Using this new concept, we are able to predict densification behavior under arbitrary temperature-time excursions following a minimal set of preliminary experiments, and to use these predictions in planning sintering strategies. Deviations of some experimental data from the master sintering curve were explained. This new developed concept was adapted in the analysis of above sintering data of alumina in and out of plasma. |
