MICROWAVE SINTERING OF MULLITE AND MULLITE ZIRCONIA COMPOSITES

摘要

The objective of this research is to evaluate microwave sintering as a viable option to process high strength mullite and mullite zirconia composites utilizing reduced time and energy. Mullite samples were sintered using a 3 K.W, 2.45 GHz microwave furnace. Sintering temperatures were in the range of 1400 to 1500°C, keeping the sintering time constant at 60 minutes. With an increase in sintering temperature from 1400°C to 1500°C, the porosity decreases from 30 to 13% and the compressive strength increases from 128±18 MPa to 387±21MPa when lwt% MgO was added as a sintering aid to mullite. Furthermore, 5 wt% yttria stabilized tetragonal zirconia (YTZP) was incorporated to prepare zirconia toughened mullite composites. A maximum compressive strength of ～ 632±29 MPa was obtained for 5 wt% ZrO2 reinforced lwt% MgO doped mullite composites sintered at 1500°C in a microwave furnace. Microwave sintering data, when compared with those of conventional sintering, revealed that localized heating of microwaves led to faster neck growth between mullite grains by surface diffusion and significantly enhanced compressive strength with a minimal change in density in mullite zirconia composites.