Ti-V-Cr與Mg-Co基BCC儲氫合金性質研究; Study on hydrogen storage characteristics of Ti-V-Cr and Mg-Co based BCC alloys

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Title:	Ti-V-Cr與Mg-Co基BCC儲氫合金性質研究;Study on hydrogen storage characteristics of Ti-V-Cr and Mg-Co based BCC alloys
Authors:	鄭榮瑞;Rong-Ruey Jeng
Contributors:	機械工程研究所
Keywords:	儲氫材料;Ti-V-Cr合金;金屬氫化物;機械合金;Mg2CoH5;bcc;Hydrogen storage materials;Ti-V-Cr alloy;bcc
Date:	2010-07-30
Issue Date:	2010-12-08 13:45:24 (UTC+8)
Publisher:	國立中央大學
Abstract:	本論文主要聚焦於Ti-V基與Mg-Co基儲氫合金進行研究，因為此兩合金系統極具潛力，可應用於燃料電池車輛及氫氣儲存，作為極佳潔淨氫氣供應源。本研究目的主要為探討微量元素添加對bcc Ti-V-Cr及Ti-V-Cr-Mn儲氫特性之影響;發展無Co殘留，以創新機械合金法製程來合成Mg2CoH5氫化物，並結合合金添加Ni及Mg2Ni及晶粒細化雙重效益，對儲氫特性影響進行儲放氫特性研究。含有0-3 at% Pd 之Ti33V33Cr34合金塊材是以真空電弧熔解製備。X光繞射分析結果顯示所有配製合金系統為單一bcc相，僅些微影響其晶格常數，其變化介於3.0297∼3.0726Å之間。添加 0.5 at % Pd之合金在80℃溫度下具有高達3.42 mass % 之吸氫量。含有0.05-3at% Pd 之Ti-V-Cr合金比不含 Pd合金有較高吸氫速率，且平台壓隨Pd含量(0.05-0.5 at%之間)之增加而微幅提升。尤其當(Ti33V33Cr34)99.5Pd0.5合金經過50次吸放氫循環測試後，放氫平台壓顯著增加。 Ti-V基儲氫合金在常溫、常壓下具有極低的放氫平台壓。因此於Ti-V-Cr合金中，藉由添加不同比率的Al、Cu 及Al-20wt%Sc母合金，研究合金添加對其晶體結構、吸放氫特性以及Ti-V-Cr-Mn合金吸放氫循環特性之影響。微量Al、Cu及Al-20wt%Sc添加於Ti-V-Cr合金中可改善其吸放氫特性。添加2at%以下Al-20wt%Sc於Ti-V-Cr合金中，在不降低其吸氫量下可顯著提升放氫平台壓。再者，以速凝法製作極細晶粒之(Ti33V33Cr24Mn10)99 (Al-20wt%Sc)1 合金，在循環吸放氫測試中，可有效抑制可逆放氫量衰退情形。針對Mg-Co 儲氫合金之研究，作者提出ㄧ種創新方法，以3Mg-MgCo2 為基材，可於相對短之球磨時間內合成Mg2CoH5。本研究針對2Mg-Co及3Mg-MgCo2 兩種材料製備及其合金吸放氫特性測試。由X光繞射結果顯示，以3Mg-MgCo2為基材經由50小時球磨及於400℃ 50atm氫氣氛下氫化15小時，可合成Mg2CoH5。經球磨之3Mg-MgCo2混合物在115℃下具有1.5 mass% 吸氫量，且在300-350℃之溫度區間放氫，可於20分鐘內達到2.0 mass%之放氫量。此結果大幅超越過去文獻報導以結合球磨及燒結程序法所製備合金之放氫速率。本研究亦使用Ni及Mg2Ni添加於3Mg-MgCo2 混合物中，藉以提升吸氫量及改善吸、放氫動力學。採用3Mg-MgCo2、3Mg-MgCo2-10wt%Ni、3Mg-MgCo2-10wt%Mg2Ni及3Mg-MgCo2-20wt%Mg2Ni為起始基材，以機械合金法製程來合成Mg-Co基合金。X光繞射分析結果顯示，在所有配製合金中，主要合成氫化相為Mg2CoH5。依據程式脫附反應(Temperature-programmed decomposition，TPD)測試結果，經球磨3Mg-MgCo2-10wt%Ni合金之放氫溫度較原來3Mg-MgCo2混合物低約35℃。此外，添加10wt% Mg2Ni於3Mg-MgCo2 混合料中，可顯著提高其吸氫量及吸氫速率，尤其改善115℃低溫下之吸氫速率。3Mg-MgCo2-10wt% Mg2Ni 合金在350℃下之吸氫量可達3.0wt%，其吸氫速率可於5分鐘內達到2.5 mass%。電子顯微鏡(TEM)分析證實，經球磨之3Mg-MgCo2-10wt%Mg2Ni 合金具有bcc結構。 The present study focuses on hydrogen storage alloys, with particular emphasis on Ti-V-based bcc and Mg-Co-based alloys, as they have the potential to be some of the most promising clean hydrogen sources for use in fuel cell vehicles or hydrogen storage applications. The main purpose of this research is to investigate the micro-alloying effects on the hydrogen storage properties of Ti-V-Cr and Ti-V-Cr-Mn bcc alloys; develop a novel route for synthesizing Mg2CoH5 hydride by mechanical alloying (MA) without leaving residual Co, and enhance the absorption-desorption properties of Mg-Co alloy by adding Ni and Mg2Ni, combining the effects of alloying and grain-refining on hydrogen storage properties. Ti33V33Cr34 ingots with 0-3 at% Pd were prepared by argon arc melting. X-ray diffraction results reveal that all of these alloys are single bcc phases, and vary only slightly in their lattice parameters, which range from 3.0297 to 3.0726Å. Ti-V-Cr alloy that contains 0.5 at% Pd exhibits a high hydrogen absorption capacity of up to 3.42 mass% at 80℃. Pd-containing (0.05-3 at% Pd) alloys have a higher rate of absorption than alloy that does not contain Pd. The plateau pressure increased slightly with Pd content in the range 0.05 to 0.5 at%; in particular, the desorption plateau pressure of the (Ti33V33Cr34)99.5Pd0.5 alloy increased significantly after the 50th absorption-desorption cycling test. Ti-V-based alloys typically exhibit a low desorption plateau pressure under ambient conditions. Therefore, various amounts of Al, Cu and Al-20wt%Sc master alloy are added to Ti-V-Cr based alloys, and the structural characteristics, hydrogen absorption-desorption properties and cycling properties of Ti-V-Cr-Mn alloy are investigated. The addition of trace Al, Cu and Al-20wt%Sc to Ti-V-Cr alloy improves its absorption and desorption properties. The addition of Al-20wt%Sc (< 2 at%) to Ti-V-Cr alloy apparently increases the desorption plateau pressure without reducing its hydrogen storage capacity. Furthermore, the fine-grain (Ti33V33Cr24Mn10)99 (Al-20wt%Sc)1 alloy produced by rapid solidification exhibits a low decline of reversible desorption capacity after cycling test. The authors’ group proposed a novel method for producing Mg2CoH5 hydride by comparative short-term mechanical alloying (MA), using 3Mg-MgCo2 mixture as the starting material. 2Mg-Co and 3Mg-MgCo2 mixtures are prepared by MA, and their hydrogen storage properties are examined. X-ray diffraction (XRD) reveals that the main phase Mg2CoH5 can be synthesized from a 3Mg-MgCo2 mixture by 50h ball milling and hydrogenation under 5 MPa hydrogen atmosphere at 400℃ for 15h. An ball-milled 3Mg-MgCo2 mixture has an absorption capacity of up to 1.5 mass% at 115℃, and a desorption capacity of over 2.0 mass% hydrogen in 20 min at temperatures from 300 to 350℃, which represents a higher desorption rate than that achieved, according to the literature, by preparation using a combined milling and sintering procedure. Pure Ni and Mg2Ni catalysts are added to 3Mg-MgCo2 mixture to enhance its hydrogen storage capacity and improve its kinetics of hydrogen absorption and desorption. A novel route was utilized to synthesize Mg-Co-based alloys by mechanical alloying, using 3Mg-MgCo2, 3Mg-MgCo2-10wt%Ni, 3Mg-MgCo2-10wt%Mg2Ni and 3Mg-MgCo2-20wt%Mg2Ni mixtures as the starting materials. X-ray diffraction of the hydride products reveals that Mg2CoH5 was the dominant hydride phase in all of these alloys. The results of temperature-programmed decomposition (TPD) reveal that the de-hydriding temperature of 10wt%Ni-containing 3Mg-MgCo2 mixture was around 35℃ lower than that of the ball-milled 3Mg-MgCo2 mixture. Additionally, adding 10wt% Mg2Ni to the 3Mg-MgCo2 mixture significantly improved both the hydrogen absorption capacity and the hydrogen absorption rate; the latter was especially improved at low temperature (115 ℃). The absorption capacity and absorption rate of the alloy 3Mg-MgCo2-10wt% Mg2Ni at 350℃ were 3.0 mass% and over 2.5 mass% in 5min, respectively. TEM analysis indicates that the ball-milled 3Mg-MgCo2-10wt%Mg2Ni mixture had a body centered cubic (BCC) structure.
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