| Popis: |
The microwave sintering (ms) process is observed to be superior to conventional sintering (cs) in the densification of Y/sub 3/Fe/sub 5/O/sub 12/ materials. A density of 97.3% theoretical density (T.D.) with pure garnet phase and small grain size (5/spl sim/7 /spl mu/m) was obtained for materials microwave sintered at 1300/spl deg/C for 20 minutes. By contrast, only 94.3% of T.D. can be reached for materials sintered by conventional processing at 1425/spl deg/C for 8 h and the grains are large (/spl sim/25 /spl mu/m). A higher densification rate in the microwave sintering process, as compared with that in conventional sintering processing, is ascribed to the lower activation energy of densification (i.e., (E/sub a/)/sub ms/=83.3 kcal/mol and (E/sub a/)/sub cs/=163.2 kcal/mol). On the other hand, small grain size in microwave sintered samples is attributed to the fact that the (E/sub a/)/sub ms/-value is smaller than the activation energy of grain boundary migration (E/sub g/=94.8 kcal/mol). |
