Transmission properties of polytetrafluoroethylene container for microwave chemical reaction

doi:10.16085/j.issn.1000-6613.2020-1586

Abstract

Abstract:

The polytetrafluoroethylene (PTFE) is widely used as a container for microwave chemical reactions because it is transmitting material with relatively low complex dielectric constant. The dielectric properties and transmitting properties of transmitting materials have an important influence on the rate and effect of microwave chemical reactions. In this article, firstly, the complex dielectric constant of PTFE in the range of 23—250℃ was measured by the resonant cavity perturbation method and the temperature characteristic of the dielectric properties of the material was analyzed. Secondly, based on the principle of electromagnetic wave transmission, the power transmission coefficient (T²) of the material affected by different factors was calculated and the transmission performance of the material were analyzed. The research showed that with the increase of temperature, the dielectric constant of PTFE gradually decreased and the loss tangent gradually increased, but the magnitude of the two changes were small. There was a Brewster angle in the transverse magnetic field (TM). When microwaves were incident at this angle of incidence, total transmission occurred. The T² in the TM polarization mode firstly increased and then decreased with the increase of the incident angle. The T² in the transverse electric field (TE) decreased with the increase of the incident angle. The overall transmission performance in TM polarization mode was better than TE polarization. As the wall thickness of the container increased, the transmission performance fluctuated and there were maximum and minimum values. Within the same container wall thickness range (0—0.1m), the wall thickness range corresponding to high transmission performance at 2450MHz frequency was more than 915MHz. The research also showed that when the incident angle of microwave was small, the T² of PTFE always remained between 0.87 and 0.99 and the transmission performance was better. Finally, this article also gave the preferred wall thickness of PTFE for reference in practical applications when microwaves were incident at different frequencies.

Key words: microwave chemistry, polytetrafluoroethylene, container, dielectric property, transmission property

摘要：

因聚四氟乙烯（PTFE）具有较低的复介电常数，其作为透波材料而被广泛用作微波化学反应用容器。透波材料的介电特性和透波性能对微波化学反应的速率和效果具有重要影响。本研究首先利用谐振腔微扰法测量了PTFE在23~250℃范围内的复介电常数，并分析了该材料介电属性的温度特性；其次，基于电磁波传输原理，计算了该材料受到不同因素影响下的功率透过系数（T²），并对该材料的透波性能进行了分析。研究表明，随着温度的增加，PTFE的介电常数逐渐减小，损耗正切逐渐增大，但是二者变化幅度较小；在水平（TM）极化中存在一个布儒斯特角θ_B，当微波以该角度入射时会发生全透射现象；TM极化下的T²随着入射角的增大先增大后减小，垂直（TE）极化下的T²随着入射角的增加而减小，TM极化下的整体透波性能要优于TE极化；随着容器壁厚的增加，透波性能波动变化，存在极大值和极小值；在相同容器壁厚范围内（0~0.1m），2450MHz频率下对应高透波性能的厚度值要多于915MHz。研究还表明，微波入射角度较小时，PTFE的T²始终保持在0.87~0.99之间，透波性能较好。最后给出了微波以不同频率入射时PTFE的优选壁厚以供实际应用过程中进行参考。

关键词: 微波化学, 聚四氟乙烯, 容器, 介电特性, 透波性能

CLC Number:

TB35

WEI Cong, SHANG Xiaobiao, ZHANG Fucheng, LIU Meihong, BAI Yongzhen, LI Guangchao, XIAO Liping, Di ZHAI, CHEN Junruo. Transmission properties of polytetrafluoroethylene container for microwave chemical reaction[J]. Chemical Industry and Engineering Progress, 2021, 40(7): 3862-3869.

魏聪, 尚小标, 张富程, 刘美红, 白永珍, 李广超, 肖利平, 翟迪, 陈君若. 微波化学反应用聚四氟乙烯容器的透波性能[J]. 化工进展, 2021, 40(7): 3862-3869.

Figures/Tables 11

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频率/MHz	θ_B
频率/MHz	23°C	50°C	100°C	150°C	200°C	250°C
915	55.296°	55.276°	55.205°	55.179°	55.147°	55.095°
2450	55.493°	55.436°	55.379°	55.341°	55.334°	55.283°

频率/MHz	θ_B
频率/MHz	23°C	50°C	100°C	150°C	200°C	250°C
915	55.296°	55.276°	55.205°	55.179°	55.147°	55.095°
2450	55.493°	55.436°	55.379°	55.341°	55.334°	55.283°

频率/MHz	厚度/m
频率/MHz	23℃	50℃	100℃	150℃	200℃	250℃
915	0~0.039	0~0.039	0~0.04	0~0.04	0~0.04	0~0.041
915	0.075~0.1	0.075~0.1	0.074~0.1	0.074~0.1	0.074~0.1	0.074~0.1
2450	0~0.014	0~0.014	0~0.014	0~0.014	0~0.014	0~0.014
	0.029~0.056	0.028~0.056	0.028~0.056	0.028~0.056	0.028~0.056	0.028~0.057
	0.071~0.098	0.071~0.098	0.071~0.098	0.071~0.099	0.071~0.099	0.071~0.099

频率/MHz	厚度/m
频率/MHz	23℃	50℃	100℃	150℃	200℃	250℃
915	0~0.039	0~0.039	0~0.04	0~0.04	0~0.04	0~0.041
915	0.075~0.1	0.075~0.1	0.074~0.1	0.074~0.1	0.074~0.1	0.074~0.1
2450	0~0.014	0~0.014	0~0.014	0~0.014	0~0.014	0~0.014
	0.029~0.056	0.028~0.056	0.028~0.056	0.028~0.056	0.028~0.056	0.028~0.057
	0.071~0.098	0.071~0.098	0.071~0.098	0.071~0.099	0.071~0.099	0.071~0.099

950MHz		2450MHz
波峰/m	波谷/m	波峰/m	波谷/m
0	0.056	0	0.021
		0.042	0.063
		0.084