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  • 學位論文

電弧法合成石墨包裹奈米鎳晶粒—使用不同含碳量之液態碳源對於包裹良率變化的研究

Study of Encapsulation Efficiency Variations on Synthesizing Graphite Encapsulated Nickel Nanoparticles by Using Different-Carbon-Content Liquid Carbon Sources

指導教授 : 鄧茂華

摘要


石墨包裹奈米金屬顆粒(Graphite Encapsulated Metal Nanoparticles,簡稱為GEM奈米顆粒),是一種殼核結構的奈米材料,其粒徑介於5至100奈米之間。GEM奈米顆粒的外層為石墨,可以保護內部的金屬晶粒免受到來自外界的酸蝕、氧化等嚴酷環境的破壞。以鎢電弧法合成GEM顆粒時,選擇以液態有機化合物取代原本的固態石墨粉與鑽石粉為碳源,所合成之GEM奈米顆粒的包裹良率可從原本的低於20%增至最高達80%。 本研究用於合成石墨包裹奈米鎳金屬顆粒所使用的五種液態碳源為:乙醇、異丙醇、正丙醇、環己烷與苯,其包裹良率分別為54.7±7.0%、69.5±4.4%、61.8±4.2%、76.5±7.3%與74.7±5.9%。分析結果發現,包裹良率會隨著各碳源單位體積的含碳量增加而提升,但當含碳量高於環己烷,則包裹良率維持在同一水平,可能的原因為碳的供給已經足量。從TEM影像得到Ni-GEM晶粒的表面形貌為圓球狀,為提供比表面積粒徑分析的其中一個假設。分別使用兩種粒徑分析方法:一為X光粉末繞射法,並由Scherrer方程式計算出平均粒徑;另一種方法為結合熱重差分析法與比表面積分析法的結果,由粒徑轉換公式算出晶粒的平均粒徑,同時也從X光粉末繞射分析法確定氧化物粉末為NiO而不是Ni2O3。得到不同液態碳源所合成的晶粒的粒徑後,從鍵解離能的觀點解釋粒徑變化,最後則是從液態碳源單位體積的含氫量與氫、氧反應後剩餘氫濃度與氧與碳反應後剩餘碳濃度的理論計算結果得出電弧合併區氫濃度最為可能影響使用高含碳源碳量其粒徑大小的因素。

並列摘要


Graphite encapsulated metal (GEM) nanoparticles are core-shell nanostructured materials with a diameter ranging from 5-100 nm. Due to the protection provided by the outer graphitic shells, GEM can survive in severely corrosive environments, under acid erosion and oxidation. The encapsulation efficiency increased substantially after replacing the diamond powder with liquid alcohol as the carbon source by using Tungsten arc-discharge. The encapsulation efficiency of GEM nanoparticles increased from lower than 20% to about 80%. In this study, five types of liquid compounds were used: ethanol, 2-propanol, n-propanol, cyclohexane and benzene; the encapsulation efficiencies were 54.7±7.0%, 69.5±4.4%, 61.8±4.2%, 76.5±7.3%, 74.7±5.9%, respectively. The results shown that the encapsulation efficiency will increase along with the carbon content, but when the carbon content is higher than cyclohexane, the encapsulation efficiency is maintained at the same level. The most possible reason is that the supply of carbon has been sufficient. From TEM images, Ni-GEM particles have a spherical surface which can be referred to as one of condition of hypothesis for particle size analysis. Two particle size analysis methods were used: one is using X-ray powder diffraction method and Scherrer equation to calculate the particle size; the other one is combining the results of thermogravimetric analysis and specific surface area analysis, then computing the particle size. Moreover, from X-ray powder diffraction analysis, it was determined that the oxide was NiO rather than Ni2O3. Comparing the relationship between dissociation energy and change of particle size, after obtaining the particle size of GEM which synthesized by different types of liquid carbon source. Finally, according to the theoretical calculation results of hydrogen content, hydrogen concentration after reaction with oxygen, and carbon content after reaction with oxygen, the factor that the residue hydrogen concentration at the coalescence region plays an important role in the change of particle size when using high-carbon-content carbon source.

參考文獻


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