Mg2(Cu1-xNix)儲氫合金結構與吸放氫特性之研究; Structural and hydrogen storage characteristics of Mg2(Cu1-xNix) alloys

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题名:	Mg2(Cu1-xNix)儲氫合金結構與吸放氫特性之研究;Structural and hydrogen storage characteristics of Mg2(Cu1-xNix) alloys
作者:	江承恩;Cheng-en Jiang
贡献者:	材料科學與工程研究所
关键词:	XRD;固溶體晶格擴張侷限;DSC;儲氫合金;Mg2(Cu1-xNix)合金;hydrogen storage alloys;Mg2(Cu1-xNix) alloys;XRD;lattice
日期:	2007-06-30
上传时间:	2009-09-21 11:28:58 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本實驗利用自行開發之恆溫揮發熔煉鑄造製程(Isothermal Evaporation Casting Process，IECP)製備高純度Mg2Cu儲氫合金，並於熔配過程中添加不同比例之Ni元素取代Cu元素進行合金改質，配製Mg2(Cu1-xNix)(X=0.2、0.4、0.6、0.8、1.0)儲氫合金，驗證IECP法於熔配過程添加第三元素之穩定度，並觀察不同Ni、Cu含量對於Mg-Cu-Ni三元儲氫合金系統之結構變化與吸放氫特性之影響。 IECP法可成功製備高純度且均質之Mg2(Cu1-xNix)合金，且由X光繞射分析得知Mg2Cu合金為Face-Centered-Cubic結構，而Ni含量的添加(X為0.2以上)，均轉變為與Mg2Ni相同之Hexagonal結構；同時合金之吸氫速率及飽和吸氫量亦隨著Ni添加量的增加而提升。Mg2(Cu1-xNix)(X=0.6、0.8)合金不同於其餘成分合金，其PCI曲線有雙平台區，且第一平台為Mg2Ni + 2H2 --> Mg2NiH4 之氫化反應，而第二平台則為2Mg2Cu + 3H2 --> 3MgH2 + MgCu2之氫化反應，然而受到固溶體晶格擴張侷限(Lattice Expansion Limitation of Additives effect)之影響使第一平台壓由300oC Mg2NiH4 之8 atm提升至15 atm以上，而第二平台壓亦由300oC MgH2 + MgCu2 之17 atm提升至25 atm，且由吸放氫前後之晶體結構變化，觀察於Mg基地之Cu元素與Ni元素其催化性質，發現Cu本身不參與氫化反應形成含Cu之氫化物，而且Cu本身會犧牲部分吸氫量。DSC曲線觀察到Mg2Cu合金之放氫溫度比純Mg放氫溫度約低20℃，表示Cu的添加能加速MgH2之放氫反應，而氫化後之Mg2(Cu1-xNix)(X=0.2、0.4、0.6、0.8)合金於放氫過程均有鑄態結構生成回復整理之吸熱反應。 This research purpose lies in preparing high-purity Mg2Cu alloy by useful method Isothermal Evaporation Casting Process(IECP) and fabricating Mg2(Cu1-xNix)(X=0.2、0.4、0.6、0.8、1.0) hydrogen storage alloys by different ratio of nickel substituting for copper in Mg2Cu alloy. It is verify that controlling addition of the third element in melting process by IECP and the effect of nickel and copper content on the structure and hydrogen storage properties for the ternary Mg2(Cu1-xNix) alloys are investigated. It is successful to fabricate high-purity and homogeneous Mg2(Cu1-xNix) alloys .Mg2Cu alloy is face-centered orthorhombic structure and Mg2(Cu1-xNix) alloys in the composition range of 1.0≧X≧0.2 are hexagonal structure. The absorption rate and capacity of the alloys increase with nickel content increasing. The PCI curves show two plateaus for the Mg2(Cu1-xNix)(X=0.6,0.8) alloys.It is found that the hydriding mechanism of the first plateau is Mg2Ni + 2H2 Mg2NiH4 and second plateau is 2Mg2Cu + 3H2 3MgH2 + MgCu2. However, lattice expansion limitation of additives effect makes that the first and second plateau pressure are raise to 15 atm from 4 atm and 25 atm from 17 atm, respectively. X-ray analysis indicate that the crystal structure are changed in hydriding process, and the catalytic character of nickel and copper element in the magnesium matrix are observed. We find out that copper isn’t concerned in hydriding reaction. Nevertheless, addition of copper makes hydrogen storage capacity reducing. From DSC curves, the dehydriding tempreature of Mg2Cu alloy is lower than pure magnesium about 20 ℃ and it announces that addition of copper can accelerate the dehydriding reaction of magnesium. Besides, the endothermic reaction that as-cast structure are formed for the hydriding Mg2(Cu1-xNix)(X=0.2,0.4,0.6,0.8) alloys in dehydriding process are observed.
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