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  • 學位論文

微波材料處理及加熱機制之探討

Microwave-Materials Processing and Heating Mechanism

指導教授 : 張存續

摘要


我們提出了一個單模式TM010空腔以釐清非熱效應, 且使用一個功率放大器為波源, 波源能量入射進入腔體, 這腔體我們有詳細討論其機制。 我們以此共振腔為基礎來量測介電係數及磁性係數藉由改良型的微擾方法, 這個改良型的微擾方法,相對上, 可容許較大樣品體積及較高的介電係數變化。 此外, 我們也利用此共振腔來加熱離子晶體(NaCl, KCl,……), 我們發現一個有趣的物理現象, 當離子晶體加熱至熔點以上時, 產生了雙層粒子環形煙霧, 它是類似水龍捲現象。這現象主要是因未來自離子晶體粒子受到離心作用力及電磁作用力交互影響, 離子晶體粒子束縛於兩個半徑之內而造成此一現象。 最後一部份工作, 我們發現離子晶體在微波場作用之下, 離子晶體熔點比傳統加熱熔點還來的低, 我們使用9種離子晶體, 這9種離子晶體在微波場下期熔點都會下降, 我們認為微波場造成離子晶體電荷分佈變形,以至於造成了熔點下降。

關鍵字

共振腔 微擾方法 離子晶體 微波

並列摘要


We have proposed a cavity with the single-mode (TM010) operation and uncovered the intriguing non-thermal microwave effect. An experiment was conducted using an amplifier rather than an oscillator as the radiation source which was injected into the applicator to enhance the electromagnetic fields. The characteristics of the applicator are discussed and the mechanism of field enhancement are illustrated and explained. We also proposed a modified calibration method to determine the complex permittivity and permeability of material based on the cavity-perturbation method. It allows a test sample with relative large in volume or high in dielectric constant. The theory is validated with a full wave solver (HFSS) and an experiment was conducted. A sample of SiC was heated using high-power microwave and characterized with low-power signal, all operating in the same cavity but different in time sequence. It facilitates the study of both microwave/material processing and material characterization. In addition, we reported an intriguing phenomenon - the particles are spouting in a strong microwave field, called the particlespout. It is similar to a waterspout, an intense columnar vortex appeared a funnel shape, is a natural wonder that attracts public attention even today. These ionic crystals (NaCl, KCl, …...) are heated in a microwave applicator with silicon carbide as the susceptor. Beyond the melting point, the particles begin to escape from the surface and move upward due to thermal convection. These particles form a funnel shape as expected but, interestingly, they have two layers. In comparison with convention furnace heating, only a single layer but unstable columnar vortex can be observed. The microwave field in the cavity is analyzed and displayed. Various configurations of the susceptors which all result in the similar behavior are studied. A theoretical model is proposed which attributes the observed phenomenon to the rotational kinematics together with the ponderomotive force. These two effects confine the particles to the inner and outer bounds, respectively. The final work, we employed microwave to process material. The microwave heating takes shorter processing time and lower processing temperature than conventional heating. The microwave-material processing is difficult to characterize because most of the researchers use over-moded applicators as well as free-running oscillators to achieve better uniformity and lower costs. This study reports the reduction of the melting points for nine alkali halide ionic crystals in the microwave fields. The melting points were determined from the abrupt change of the reflected wave due to the detuning of the input microwave frequency and the resonant frequency of the cavity during the phase transition. The reduction of the melting points were systematically characterized, where the lowest reduction is less than 2% for lithium bromide (LiBr) and the highest reduction is greater 5% for potassium fluoride (KF). The bond length of the ionic crystal strongly correlated to the reduction ratio of the melting temperature. A theoretical model is proposed which considers the energy drop due to the electric dipole of the ionic crystal interacting with the applied microwave fields. The proposed model qualitatively explains the melting point reduction, but more elaborated theory is still needed.

參考文獻


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