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Microwave Enhancement Effects

Author: langfeng Time: 2018-09-25

Microwave Enhancement Effects

There have been numerous reports of enhancement of sintering kinetics when using microwave processing. Probably the most startling is a report of as much as a 400 ºC reduction in sintering temperature along with a dramatically reduced activation energy for Al2O3 processed in a 28-GHz microwave cavity (Janney and Kimrey, 1988, 1990). As discussed in Chapter 3 of this report, significant errors in temperature measurement can lead to misleading processing results. Shielded and grounded thermocouples, as discussed in Chapter 3, as well as optical pyrometers, were used to minimize temperature-measurement errors, and carefully designed insulation systems were used in the studies referenced above to minimize temperature gradients. By switching the microwave power off and on, and observing thermocouple response, it was demonstrated that the microwave field did not bias the thermocouple output (Janney et al., 1991a). While temperature measurement may yet be a problem, it is difficult to imagine a 400 ºC error.



Significant reductions in sintering temperatures or enhancements in the diffusion coefficient for sintering have also been reported for Al2O3 (Patil et al., 1991; Cheng et al., 1992)

and Al2O3 doped with MgO (Cheng et al., 1992). Reductions in sintering temperature and activation energy have been reported for the sintering of zirconia-toughened alumina (Kimrey et al., 1991) and zirconia (Janney et al., 1991b, 1992a). A variety of other ceramics were similarly sintered using microwaves, including B4C (Holcombe and Dykes, 1991a), LaCrO3 (Janney and Kimrey, 1992), and Si3N4 (Tiegs et al., 1991; Kiggans et al., 1991; Kiggans and Tiegs, 1992). These results, for a broad range of materials, indicated that the reduction in sintering temperature was observed in insulators and ionically conducting materials but not in electronically conducting materials. Reductions in sintering temperature and activation energy were greater at 28 GHz than they were at 2.45 GHz.


Changsha Langfeng Microwave Technology Co., Ltd.



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