Temperature Assessment Of Microwave-Enhanced Heating Processes

Abstract

In this study, real-time and in-situ permittivity measurements under intense microwave electromagnetic fields are proposed as a powerful technique for the study of microwave-enhanced thermal processes in materials. In order to draw reliable conclusions about the temperatures at which transformations occur, we address how to accurately measure the bulk temperature of the samples under microwave irradiation. A new temperature calibration method merging data from four independent techniques is developed to obtain the bulk temperature as a function of the surface temperature in thermal processes under microwave conditions. Additionally, other analysis techniques such as Differential Thermal Analysis (DTA) or Raman spectroscopy are correlated to dielectric permittivity measurements and the temperatures of thermal transitions observed using each technique are compared. Our findings reveal that the combination of all these procedures could help prove the existence of specific non-thermal microwave effects in a scientifically meaningful way.

Evolution and Analysis of Dielectric Properties of Typical Materials Under Strong Microwave Field

“…10. It is easy to find that the InP and GaAs samples have has a nonlinear temperature rising characteristics within the studied power range, and the temperature variation ranges from room temperature to about 80 • C, not exceeding 90 • C. However, the temperature of the Al 2 O 3 and BN samples in the experiment did not change more than 2 • C. Here gives two points description about the temperature acquisition: (1) in reference [31], the temperature is detected from the quartz tube, and the sample temperature is obtained by calibration algorithm. In this paper, we obtain the temperature of the sample directly; (2) from the Fig.…”

“…In this paper, we obtain the temperature of the sample directly; (2) from the Fig. 6 in [31], we can find that the surface temperature and the body temperature of the sample are of highly consistency in the low temperature zone (less than 200 • C). Therefore, the temperature obtained by the above method is reliable.…”

High Temperature Dielectric Properties of Iron- and Zinc-Bearing Products during Carbothermic Reduction by Microwave Heating

“…An IR pyrometer (OPTRIS GmbH, Berlin, Germany) measures the surface temperature of the quartz holder from the lateral through an inspection hole in the cavity wall. A thorough calibration procedure is applied to obtain the bulk sample temperature from surface temperature measurements [20]. In order to measure the dielectric properties during the carbothermic reduction process, the samples are placed in a quartz holder and inserted in the microwave cavity through an insertion hole.…”

“…This technique presents several disadvantages: (i) the sequence of reactions followed under conventional heating may not be representative for the microwave process; (ii) the sample unavoidably cools down during the measurement, especially at high temperatures (>500 • C) [19]. These problems increase the measurement uncertainty and make this technique inadequate if the material undergoes fast or irreversible changes at certain temperatures, because the change of properties can be lost during sample movement, or measured temperatures can mislead the interpretation of the sequence of reactions [19,20].…”

Evidence of a new phase in gypsum–anhydrite transformations under microwave heating byin situdielectric analysis and Raman spectroscopy

“…The bulk sample temperature was calculated from the quartz holder surface measurement by following a calibration curve obtained in a thorough procedure described in ref. 63.…”