Abstract
本研究的目的在於利用多孔陶瓷材料進行與水吸附相關的應用,實驗所用 的陶瓷片由高嶺土,陶瓷纖維以及甲基纖維素以不同比例乾壓燒結製成.主 要研究偏重在濕度偵測計的研發以及其多孔結構對偵測結果的關係,以求 最佳的偵測表現.另外利用多孔陶瓷對水的吸附能力進行空氣除濕的評估 實驗,以及土壤中水勢能偵測的可行性實驗. 在濕度偵測計應用方面,製 作出的陶瓷片為厚度約0.5mm,邊長23mm的正方形薄片,兩面以金濺鍍當作 電極.在偵測性質上以交流阻抗測量電阻,以陶瓷體在不同濕度下的電阻當 作濕度的指標,實驗評估電阻變化的靈敏度,再現性以及偵測反應時間.影 響偵測表現的微結構因素包括材料的表面積,孔徑分佈,孔隙度以及表面反 應性.實驗結果顯示平均靈敏度在相對濕度從10%到90%達10的五次方歐姆, 成份組成以陶瓷纖維28%,甲基纖維素28%,高嶺土44%為最佳,孔隙度40%左 右.再現性以反覆偵測結果尚可接受.反應時間則略遜於市售濕度計,主要 是因微孔中水份擴散造成.根據水分子在孔洞中的行為以及實驗結果我們 發現,在低濕度下影響偵測表現的因素為多孔材料的表面積,主要是因吸附 現象造成. 在高濕度下則因凝結現象所以孔徑分佈成為決定因素.另外陶 瓷固體粒子的連通性影響電荷傳遞路徑,孔隙度在45%以上的樣品實驗結果 顯示電阻較高,但吸附量並未較低.表面分析顯示表面鈉離子存在,在水吸 附層中扮演電荷傳遞的角色. 在空氣除濕應用方面,以不同孔徑和孔隙度 進行實驗發現除濕率差異不大,同時實驗顯示以5000~6000ml/min的流量除 濕可得最佳平均除濕率.對於土壤水勢的測量,再現性並不理想,但應有實 用改善的空間. The objective of this study is to find applications of porous ceramics in fileds related to water adsorption. This ceramic material is made of different ratios of kaolin, ceramic fiber, and sodium carboxylmethyl cellulose(CMC) by dry-pressing method and sintering. The focus of this thesis is on the applicationas a humidity sensor and the correlation between processing, microstructureand sensing properties to achieve the best sensing performance. Research in thefeasibility of air- drying and measurement of the water potential in soil werealso included. In the application as a humidity sensor, a square ceramicpieces of 23*23*0.5(mm) was first prepared. Au electrodes were then sputteringring coated on the both sides. The sensor's resistance which was measured by acimpedance was recorded as a function of ambient humidity. The sensitivity, reproducibility, and response time of humidity sensing were studied. The micro- structure characteristics involved are specificarea, pore size distribution, porosity, and surface Na content of the sensor material. Our experimental results showed an average sensitivity of 10(5) ohm as relative humidity changed from 10% to 90%. The optimal component is ceramic fiber 28%, CMC 28%,kaolin 44% and a porosity around 40%. Reproducibility is satisfactory. Response time is slightly longer than the commercial sensor due to water molecules diffusion inside micropores. According to the microstructure and behavior of water molecules in pores, we can see that the specific surface area is the key parameter under low humidity due to water adsorption effect, while the microporous pore volume is the main factor under high humidity due to capillary condensation. The connection of solid grains affects the path of conductance is also an important microstructure. Porosity larger than 45% show higher resistance because of poor connection, although the adsorption quantity is high. Surface analyses show that the sodium content on surface plays the role as charge carrier in the water adsorption layer.In the application of air-drying application, preliminary results indicated that the difiference between different discs were not significant. These porous discs exhibited optimal drying effects at the volumetric flow rate of 5000~6000 ml/min. As for soil water potential measurement, early experiments did not produce reliable results, leaving rooms for further improvements.