連續式控制潛弧奈米合成系統製備銅基奈米流體與性質研究

Fabrication and Analysis of Cu-Based Nanofluids Prepared by a Continuously Controlled Submerged Arc Nano Synthesis System

羅志宏(Chih-Hung Lo)

指導教授 ： 鍾清枝

國立臺北科技大學/機電學院/機電科技研究所/博士(2006年)

摘要

依發展奈米科技而言，製備奈米材料為首要關鍵。本研究之目的在發展一套利用環境壓力差原理以及在恆壓、恆溫下可連續製備出奈米流體的合成系統，即連續式控制潛弧奈米合成系統(CC-SANSS)。此套系統之主要裝置單元包括電弧產生器與伺服控制單元、參數控制單元、恆壓控制單元、恆溫控制單元、線上介電液導電度量測單元、製程資料回饋單元、介電液自動供給單元及奈米流體收集單元等。本系統利用介電液之比電阻品質作為連續控制的核心，為了提升奈米流體產量，以及製備微粒尺寸分佈小與分散性佳的奈米流體。本文針對製程參數電壓、電流、放電頻率、介電液溫度及介電液比電阻品值，運用田口法做最佳化的實驗進行試誤法製程參數分析比對，以獲得最佳之奈米流體合成參數。
研究結果顯示，已建立奈米微粒的平均粒徑與介電液比電阻品值之關係，將比電阻1255 與2600 分別定為奈米流體取樣與介電液供給的控制參數。配合穩健性實驗，以最佳製程參數可製備出平均長度 nm寬度 nm之類針狀氧化銅奈米微粒懸浮於去離子水中，以1.2 L/hr 且0.8重量百分濃度產出。本研究利用不同比例之去離子水與乙二醇作為介電液，依據不同之熱傳導特性，可以製備出不同形貌之銅基奈米流體，同時也以成長面的理論機制加以解釋。此外，氧化銅奈米棒也在控制介電液溫度時被製備出，以低溫-5℃之條件製備長度1-2 寬度30-50 nm之氧化銅奈米棒。
本系統製備之氧化銅奈米流體的pH值為6，此值遠離pH9.5 0.4之零點電位，且在靜置一年以上的長時間觀察，仍可維持良好之懸浮特性。此外，為了解氧化銅奈米流體受環境溫度之穩定性影響，本研究設計一套恆溫裝置於室溫以下工作溫度檢測奈米流體之穩定性與熱傳導，20℃為奈米流體最適合的工作溫度，越低溫之環境溫度將影響奈米流體之穩定性。
探討添加奈米微粒在不同體積濃度與溫度條件下，針對其熱傳導係數進行實驗分析。在奈米流體體積濃度影響方面，樣本溫度40℃時，0.1 Vol.%能提升熱傳導係數2.5%，當濃度上升到2.0 Vol.%時，則能提升到40.03%，濃度對於熱傳導係數的增進率均呈現正比關係。在實驗樣本溫度影響方面，濃度2.0 Vol.%時，樣本5℃時能提升熱傳導係數21.47%，當溫度上升到40℃時，則能上升到40.03%。本研究所使用的氧化銅奈米顆粒外型為類針狀，非對稱的顆粒外型有助與液體分子間發生更劇烈的擾動，可進一步推論不但顆粒的大小會影響熱傳導係數，顆粒的外型同樣也會影響熱傳導係數的提升。同時0.1-2.0 Vol. %之氧化銅奈米流體與0.1-0.5 Vol. %銅奈米流體，在溫度5-40℃與剪應率75-900 下依舊呈現牛頓流體的流變行為。
本研究亦以電泳披覆法，將連續式控制潛弧奈米合成系統製備的奈米氧化銅流體披覆於不鏽鋼基材上並探討披覆膜的性質。可以在 mm的鏡面不鏽鋼基板上披覆一氧化銅披覆膜，燒結溫度至300℃時，氧化銅奈米顆粒會有燒結的現象產生，且升溫速度太快會使得披覆膜緻密性無法得到有效的改善，故以2℃/min燒結至200℃可得一表面緻密性較佳的披覆膜，奈米氧化銅披覆膜經光吸收測試實驗後發現在可見光420nm波長下有比較強的吸收能力，且吸收強度隨著披覆時間的增加而有正比的趨勢。

關鍵字

奈米合成系統 ； 奈米流體 ； 田口法 ； 熱傳導率 ； 流變 ； 電泳披覆

並列摘要

Preparation of nano-materials is one of the most significant matters for the development of nano-technology. In this dissertation, a continuously controlled submerged arc nano synthesis system was proposed and developed, using the principle of pressure difference of the operating condition maintaining, a constant pressure and an isothermal environment. The synthesis system device mainly comprises an arc generator and servo control unit, a parameter control unit, a constant pressure control unit, an isothermal control unit, a manufacture data feedback unit, an on-line conductivity measurement unit, an automatic liquid refilling unit and a sampling unit. In order to increase the production amount of nanofluids, the synthesis system was designed to operate continuously to synthesize nanofluids with a small particle size and uniformly dispersed distribution. The specific electric resistance of dielectric liquid is the key factor for the proposed continuous preparation. In addition, experiments based on Taguchi method were conducted to investigate the key parameters, such as electric voltage, electric current, pulse-duration frequency, dielectric liquid temperature and specific electric resistance of the dielectric liquid. Furthermore, Taguchi method was used to investigate the optimum process parameters to prove try- and- error process.
Experimental results show a close relationship between the electric resistance of dielectric liquid and the nanoparticle size. The electric resistances of sampling and refilling liquid were set at 1255 and 2600 , respectively. Using the robust design method and the optimized process parameters, the size of the prepared needle-like shape CuO nanoparticle was found nm in length and nm in width. In addition, the 1.2 L/hr nanofluids with a concentration of 0.8 w. t. % can be prepared using the developed technique. According to the different thermal conductivity, mixing solution of de-ionized water and ethylene glycol can be used to prepare different shapes of Cu-based nanopaericles. The growing faces theory of the relationship between the type of dielectric liquid and the morphology of the prepared Cu-based nanoparticles was carefully studied and analyzed. Furthermore, we control the temperature of dielectric liquid to prepare CuO nanorods. A length of 1-2 with a width of 30-50 nm of CuO nanorods can be prepared under a low temperature condition at -5℃.
The pH of the as-prepared CuO nanofluids is 6, which is greatly different to that of isoelectric point (IEP) about pH9.5 0.4. These nanofluids can be well suspensed in the liquid for longer than one year. Furthermore, this study also employs an ambient temperature controller to maintain a low temperature of the working environment and to record data on the motion behavior of suspended nanoparticle for analysis of its stability. Results show that the most stable working condition for preparation of the as-prepared CuO nanofluids is at 20℃. It was identified that the stability of nanofluids will deteriate when the temperature drops lower than 20℃.
This dissertation also examined the thermal conductivity of nanofluids containing copper oxide of different volume fractions and at different specimen temperatures. The experimental results showed that both volume fraction and specimen temperature of nanofluids are linearly related to thermal conductivity. When specimen temperature was set at 40

並列關鍵字

Nano synthesis system ； Nanofluids ； Taguchi approach ； Thermal conductivity ； Rheology ； Electrophoretic deposition

參考文獻

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