Temperature measurements during microwave processing: The significance of thermocouple effects

Reliable and accurate temperature measurement during microwave processing o f ceramic bodies is controversial. Although thermocouples are routinely use d in conventional thermal furnaces, their presence in microwave furnaces ca n locally distort the electromagnetic field, conduct heat away from the sam ple, induce thermal instabilities and microwave breakdown, and lead to seri ous measurement errors. These thermocouple effects have been studied and fo und to be more pronounced in low- and medium-loss ceramic materials. To dec rease the thermocouple effects during the processing of advanced ceramic ma terials, an optical, noncontact temperature sensing system has been develop ed, calibrated, and incorporated into a computer-controlled microwave furna ce.