脈衝式電源之平板型介電質常壓電漿束特性分析及利用其後放電區域的應用研究

Abstract

本論文探討自組的脈衝式電源驅動的平板型介電質常壓電漿束 (氮氣為主)，及電漿束的後放電區域特性分析及其應用之研究。特性分析主要包括拍照直接觀察、電性量測 (電壓及電流波型，電漿吸收功率) 、光譜量測 (OES及FTIR) 、氣體溫度量測 (熱電偶線及OES)與臭氧濃度量測。量測顯示純氮DBD電漿產生大量亞穩態氮氣，逐漸加入氧氣後產生大量臭氧。同時，根據後放電區域量得的光譜特性，吾人成功地瞭解相關電漿化學反應機制。了解這些反應機制對表面處理相關的應用是相當重要的。此研究使用氮氣為主的平板型介電質常壓電漿束的應用研究包括PP薄片親水性改質、ITO玻璃表面清潔、E. coli/ B. subtilis殺菌與B. subtilis孢子滅菌。結果顯示這些特性對於應用有很大效率影響，簡單的敘述如下。 在靜止PP薄片表面親水特性處理方面，以氮氣為主 (氧氣/氮氣比小於1%) 平板型DBD常壓電漿束處理後 (處理距離小於10 mm，處理時間5秒)，接觸角從原先103度降至30度。處理後PP薄片靜置24小時後接觸角恢復至40度。同樣電漿條件對靜止的ITO玻璃表面處理，結果顯示 (氧氣/氮氣比) 有兩個區域接觸角從84度降至20-30度。第一區域為氧氣/氮氣比小於0.05%，處理距離6-16 mm。第二區域為氧氣/氮氣比超過0.06%，處理距離2-10 mm。量測結果顯示: (1) 於後放電出口 10 mm內，亞穩態氮氣[ ]與臭氧光分解反應均扮演主要角色對於表面處理，而相關電漿反應過程需再進一步研究釐清。(2) 遠離大於後放電出口 10 mm，對於ITO玻璃清潔及PP薄板表面親水改質，亞穩態氮氣扮演了主要角色。XPS量測結果發現，經過平板型DBD常壓電漿束處理後的試片隨O/C比增加而更加具有親水性。 在E. coli與B. subtilis殺菌的應用，結果顯示與前人在放電區域的研究相較後放電區滅菌效率仍然相當優異，毫無遜色。主要關鍵在於電漿放氣體中需要加入氧氣以產生足夠量的臭氧增加滅菌效率。此外使用空氣平板型介電質常壓電漿束的滅菌效率比氧氣電漿好，可能與空氣電漿中含有氮氧化物與臭氧同時對滅菌作出貢獻。在E. coli 與B. subtilis (10^7 CFU/mL)存活率實驗方面，經過氧氣及空氣電漿處理小於18次 (等效停留時間1.8秒)，距離介於4-20 mm，均可以使菌種達到完全失活(inactivation)。在B. subtilis 孢子(10^5 – 10^7 spore/mL)滅菌實驗方面，經過加入2%四氟化碳的空氣電漿對孢子滅菌處理效果相當優異(單純空氣電漿處理幾乎完全無效)。經過2%四氟化碳的空氣電漿處理小於10次 (等效停留時間1秒)，距離14 mm，均可以達到完全滅菌。間接證明應有不少高化學反應性自由基 (如氟原子)，存在放電及後放電區域。 總結來說，本博士論文在實驗上針對氮氣為主的平板型介電質常壓電漿束自組架設完成及有效的特性分析，成功地利用其後放電區域進行應用的研究。與前人大部分直接利用放電區域進行分析與應用的研究相較，本論文相對是較獨特的。同時在論文最後章節亦條列出建議未來應進行研究的研究部分。

Development, characterization of a planar atmospheric-pressure nitrogen-based dielectric barrier discharge driven by a quasi-pulsed (distorted sinusoidal) power source and its applications using the post-discharge jet region are presented in this PhD thesis. The characterizations of the DBD system included the measurements of the direct image visualization, the electrical properties (current-voltage curve and power absorption), the optical properties (optical emission spectra and FTIR), the gas temperatures (thermocouple and optical emission spectra), and the ozone concentration. The measurements showed that abundant mestastable nitrogen was generated in the pure nitrogen DBD, while abundant ozone was created as long as the oxygen was added. Specially, observation of optical emissions in the post-discharge jet region was successfully explained by several kinetic mechanisms, which is important in understanding the fundamental mechanism in surface modification. This DBD system was then applied to several important applications, which included the modification of hydrophilic property of PP film, the surface cleaning of ITO glass, the inactivation of E. coli, B. subtilis and the sterilization of B. subtilis spore. Results of applications showed that the developed DBD system was highly effective in these applications under proper operating conditions, which they are briefly described in the following in turn. For the stationary PP films, the contact angle (CA) decreases dramatically from 103□ (untreated) to less than 30□ (treated) with a wide range of O2/N2 ratios (< 1%) and treating distances (< 10 mm). In addition, the CA can still be maintained at ~40□ after 24 h of the aging test. For the stationary ITO glass, show that there exists two distinct regimes with lower CAs in the range of 20-30° (84° for untreated). The first one was the regime with an oxygen addition of less than 0.05% and a treating distance in the range of 6-16 mm. The second one was the regime with an oxygen addition larger than 0.06% and a treating distance in the range of 2-10 mm. The measurements showed that: 1) in the near jet downstream location (z<10 mm), both the metastable N2 and ozone photo-induced dissociation played dominant roles in surface modification, although their relative importance was unclear and requires further investigation; and 2) in the far jet downstream location (z>10mm), when the ratio of O2/N2 was small, only the long-lived metastable N2 played a major role in ITO cleaning and PP film surface modification. XPS measurements showed that improved hydrophilic property was obtained after DBD jet treatment with increasing O/C ratio. For the inactivation of E. coli and B. subtilis, the results showed that the post-discharge jet region is very efficient in inactivating these two bacteria as previous studies using the discharge region, should the working gas contains appreciable oxygen addition, which in turn generates abundant ozone. In addition, the inactivation is more effective by using compressed-air APPJ as compared to that by oxygen APPJ, possibly through the assistance of nitrous oxide existing in the former. Results of survival rate show that both E. coli and B. subtilis bacteria (up to 10^7 CFU/mL) can be effectively inactivated using less than 18 passes (1.8 seconds of residence time in total) of exposure to the post-discharge jet region of compressed air and oxygen discharges at different treating distances in the range of 4-20 mm. For the sterilization of B. subtilis spore, the results showed that addition of only 2% CF4 into the air DBD is found to be very effective, which was otherwise very ineffective using the pure air DBD. It was found that the CF4/air (2%) APPJ treatment resulted in the efficient inactivation of the B. subtilis spores after 10 passes (residence time: 1.0 s) exposures for treatment distances (14 mm). Indirect evidence showed that highly reactive atoms, such as F atoms, were generated in the discharge and in the post-discharge jet region. In conclusion, in the current thesis, a simple yet very effective planar nitrogen-based DBD system under atmospheric-pressure condition is presented and characterized experimentally. It was successfully applied using its post-discharge jet region, which was rarely seen in the literature, for surface modification and inactivation/sterilization. Recommendations for the future study are also outlined at the end of the thesis.