這項研究主要是利用超臨界二氧化碳混和液態水與液態有機酸，來製作奈米孔洞材料。利用磁控濺鍍的方式在矽基板上鍍上銀鋁合金薄膜，其製作之薄膜的元素莫耳比為Ag35Al65、Ag50Al50與Ag65Al35。並將薄膜放置在反應槽當中，反應槽中同時加入約0.25毫升的水或酸。接著將高壓二氧化碳通入反應槽，並同時提升反應槽溫度至120oC，形成超臨界二氧化碳。由於水在超臨界二氧化碳中的溶解度相當高，溶於超臨界二氧化碳的水具有非常強的氧化力且含有微量的碳酸根，因此將與銀鋁合金薄膜進行反應。反應過程中銀鋁薄膜將被選擇性的腐蝕，其中的鋁以及Ag2Al會被腐蝕掉，剩下銀枝條。然而，利用水融入超臨界二氧化碳的腐蝕實驗過於耗時，需要1小時以上方能有明顯的效果。因此，若在反應槽之中加入草酸，其草酸會與鋁反應，並且在更短的時間之內生成孔洞。得到的孔洞材料我們將用XRD、SEM與BET進行材料分析。我們發現只Ag35Al65能被超臨界二氧化碳中的水腐蝕，其孔洞大小為300 nm-500 nm，而Ag35Al65、Ag50Al50與Ag65Al35在經過超臨界二氧化碳中的微量草酸腐蝕後，孔洞大小為100 nm-500 nm，孔洞率分為72%、49%與32%。此外反應槽的壓力升高，會提升選擇性腐蝕的速度，透過SEM觀察，可知2000 psi明顯快於1600 psi。由於超齡界流體具有非常低的表面張力，因此他能夠滲透至相當細微的孔洞，因此銀比例較高的Ag50Al50與Ag65Al35，也能經由超臨界腐蝕達到去合金之作用。

In this research, the nanoporous silver foams are fabricated by dealloying the Ag-Al thin films in supercritical (SC) carbon oxide. The Ag-Al thin films were deposited by sputtering with different compositions of Ag35Al65, Ag50Al50 and Ag65Al35 (in atomic percentage, at%). After the thin films are formed, they are set in a reaction chamber filled with supercritical carbon oxide. The supercritical carbon oxide is a mixture with water. Water has high solubility in SC CO2, and both water and CO2 are common materials we can gain in nature. Normal reverse osmotic water has carbonate (CO32-) inside because a small amount of CO2 gas in the atmosphere dissolved in water. The water has strong oxidative capacity in SC CO2, which could react with alumina and form the pore with the size from 300 nm-500 nm. In this research, we also choose H2C2O4 aqueous solution as the solute in the SC CO2 reaction chamber. The foam analyses were done by SEM, XRD and BET. The surface value of the as-dealloyed Ag35Al65, Ag50Al50 and Ag65Al35 are 4.5, 3.1, 2.6 m2g-1 respectively, and the porosity volume fraction values are 72%, 49%, 32% respectively. It takes less time to form a nanoporous structure, and the pore size is only 100 nm-300 nm. As we increase the pressure of the chamber, the corrosion rate will be raised as well. Due to the small tension of supercritical fluid, the supercritical fluid dealloying process is able to form nanoporous silver when the alloy has higher silver compositions like Ag50Al50 and Ag65Al35, for which the typical chemical dealloying is not able to do so.

中文摘要 i
Abstract ii
Table of content iii
List of Tables v
List of Figures vi
Chapter 1 Introduction 1
1.1 Nanoporous materials 1
1.2 Supercritical fluid 3
1.3 Motivation 4
Chapter 2 Background and literature review 7
2.1 Corrosion 7
2.1.1 Introduction 7
2.1.2 The corrosion behavior of Al-Ag alloys 9
2.1.3 Corrosion in supercritical CO2 9
2.1.4 Water in supercritical CO2 10
2.2 Dealloying 11
2.3 Supercitical Fluid 15
2.3.1 Supercritical fluid solvent 15
2.3.2 The surface tension of supercritical CO2 16
2.3.4 Supercritical CO2 17
2.3.5 Water solubility in supercritical fluid 20
2.4 Chemical dealloying by SCFs 20
2.4.1 Metal corrosion in a supercritical carbon dioxide 20
2.4.2 Supercritical carbon dioxide corrosion to fabricate nanoporous structure 21
2.5 Technique for characterization of thin film porosity 21
2.5.1 X-ray reflectivity and small angle x-ray scattering 21
2.5.2 Surface acoustic wave 22
2.5.3 Specific surface area and pore size distribution analyzer, BET 23
2.5.4 Image analysis 24
Chapter 3 Experimental procedures 25
3.1 Sample preparation 26
3.1.1 Multi-target sputtering 26
3.1.2 The supercritical equipment 27
3.2 Analyses 29
3.2.1 X-ray diffraction (XRD) 29
3.2.2 Scanning electron microscopy (SEM) 30
3.2.3 Qualitative and quantitative composition analyses 30
3.2.4 Image analysis 31
3.2.5 BET test 31
Chapter 4 Results and discussion 33
4.1 XRD analysis 33
4.2 Microstructure and composition analyses 34
4.3 HCl in supercritical fluid 37
4.4 Typical chemical dealloying and supercritical fluid dealloying 38
4.4.1 Typical chemical dealloying and supercritical fluid dealloying of HCl 38
4.4.2 The corrosion time and pore size 40
4.4.3 Corrosion results after raising the Ag content 41
4.5 Selective etching after the annealing 41
4.6 Porosity and surface area analyses 42
Chapter 5 Conclusion 44
References 46
Tables 51
Figures 57

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