臺灣博碩士論文加值系統

本研究係利用三元系NaCl-KCl-MgCl2熔融氯化物電解質浴進行脈衝電解鎂金屬之研究，含三元系熔融鹽之電化學循環伏安法量測與三元系熔融鹽之鎂電解沉積，及使用脈衝電流值為2A、2.5A、3A、3.5A、4A分別量測電流效率。依實驗結果比較，選擇以脈衝電流值為3A、Duty Cycle 50%為電解條件。添加NH4Cl於融熔鹽浴中，依循環伏安圖得知，隨著NH4Cl添加融熔鹽浴的還原電位窗有增大趨勢，此情形有利於鎂金屬的還原及提升鎂金屬純度，其中以添加35 mole% NH4Cl可得到較佳純度的鎂金屬。鎂電解實驗以MgCl2-(NaCl-KCl)組成為40:60 mol%做為電解質浴，以碳棒為陽極、不鏽鋼棒為陰極，電解操作溫度973K，脈衝電流值為3A、Duty Cycle為50%時，進行脈衝電解沉積鎂金屬，所得電流效率值較佳。此外，添加NH4¬¬Cl後脈衝電解製備的鎂金屬純度可達99%，可歸因於NH4Cl加熱分解時，產生的氣體時會除電極表面的雜質，且分解出來的Cl2具有純化融熔鹽浴的效果，故可提升鎂金屬純度。

In this study, the magnesium metal electrodeposited by using the pulse electrolysis with the electrolyte bath of ternary system molten chlorides of NaCl-KCl-MgCl2, and the measurement and analysis of ternary system molten salt are carried out by the electrochemical cyclic voltammetry; moreover, the electrodeposition and analysis of magnesium will also be discussed. The current efficiency is respectively measured when the pulse current values are 2A, 2.5A, 3A, 3.5A and 4A, and from the analysis of these results, the pulse current value 3A and the duty cycle 50% are selected as the pulse electrolysis conditions. From the analysis of cyclic voltammetry, it shows the potential window of molten salt with adding NH4Cl tends to go up, and the result is beneficial to the reduction of magnesium and promote the magnesium metal purity. In this study, the electrolyte bath is composited by proportion of 40:60% for MgCl2-(NaCl-KCl), and the carbon rod acts as anode, and the stainless steel rod acts as cathode. The pulse electrolysis is proceeded to electrodeposite magnesium metal when the temperature of electrolysis is 937K, the pulse current value is 3A and the duty cycle is 50%, the best current efficiency obtained on the condition. However, the purity of the magnesium metal prepared by pulse electrolysis can be achieved 99%. It is the cause that when the NH4Cl is decomposed to gas phase which included NH4 and Cl2, and the electrodes are cleaned by this gas phase; moreover, the Cl2 can also increase the purity of the molten salt. So the purity of the magnesium metal is increased.

目錄

中文摘要.............................................................i

ABSTRACT...........................................................ii

誌謝................................................................iii

目錄.................................................................iv

表目錄...............................................................vi

圖目錄..............................................................viii

符號說明.............................................................xii

ㄧ、緒論..............................................................1

1-1 電化學系統.......................................................1

1-2 電化學電解槽(Electrochemical cell).................................2

1-3 電化學之相關參數說明.................................................5

1-4 熔融鹽之定義........................................................6

1-5 鎂金屬與鎂合金之製備方法.............................................13

1-6 鎂金屬的應用.......................................................14

1-7 研究動機與目的......................................................15

1-8 研究架構...........................................................16

二、文獻回顧............................................................18

2-1 熔融鹽電化學........................................................18

2-2 熔融鹽電解之優點(Advantages of Fused Salt Electrolysis)..............19

2-3 脈衝電解電鍍.........................................................20

2-4循環伏安法(cyclic voltammetry)........................................21

2-5庫倫法...............................................................22

2-6 電解質阻抗(Electrolyte resistance)...................................23

2-7 電解槽設計(Electrolyzer design)......................................23

2-8 輕金屬(Light metal)..................................................33

2-9 輕金屬之製備(Electrowinning)..........................................34

2-10 熔融鹽組成的選擇......................................................37

2-11 鎂金屬的純度提升......................................................38

2-12 電流效率的提升........................................................39

三、實驗方法與步驟..........................................................41

3-1 實驗藥品..............................................................41

3-2 實驗設備..............................................................42

四、結果與討論.............................................................50

4-1 電解效率量測...........................................................50

4-2 電解效率量測¬-Duty Cycle 分析...........................................61

4-3 電化學行為量測-添加NH4Cl分析.............................................63

4-4 電流效率量測-添加NH4Cl分析...............................................69

4-5 AA純度分析.............................................................72

4-6 EDS分析...............................................................75

五、結論...................................................................77

六、未來展望................................................................78

參考文獻...................................................................79

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