【作者】 李长友；

【导师】 刘江文；

【作者基本信息】 华南理工大学 ， 材料加工工程， 2011， 硕士

【摘要】 镁基储氢材料具有储氢量大、价格低廉等优点,但其氢化物热力学稳定性高、吸放氢温度高和动力学性能差等缺点,限制了它的实验应用。本文在对国内外镁基储氢材料的研究进行综述的基础上,研究了Mg_88.4Y_5.6Zn₆（at.%）合金的储氢性能以及吸放氢前后的相结构转变。采用感应熔炼方法制备Mg_88.4Y_5.6Zn₆（at.%）合金,利用X射线衍射（XRD）、扫描电子显微镜（SEM）、能谱（EDS）、透射电镜（TEM）等手段,研究了Mg_88.4Y_5.6Zn₆（at.%）合金微观组织形貌,吸氢过程与放氢过程的相转变;测定了合金的压力-组成-温度（PCI）曲线;获得了基本的热力学数据;并对吸放氢机理做了初步探讨。铸造Mg_88.4Y_5.6Zn₆（at.%）合金的铸态组织由镁固溶体、长周期结构X相（LPSO）以及粗大的共晶组织组成。长周期结构X相（LPSO）呈板条状,大量的LPSO结构连接成网格,其主要相为Mg₁₂YZn。镁固溶体呈现颗粒状,镶嵌于板条状结构中。非平衡的共晶组织由Mg、Mg₃Y₂Zn₃相组成。合金经450°C×48h退火处理后,相组成并未发生变化,依然由Mg固溶体、LPSO以及Mg₃Y₂Zn₃组成。非平衡的共晶组织溶解,由原来的粗大形态变得纤细和呈不连续状;LPSO长周期结构也有碎化的趋势,而且含量有所减少;Mg固溶体由原来的颗粒状变为不规则形状。球磨可以使合金的组织细化,球磨后的样品呈颗粒状,颗粒大小约为40μ～70μ。铸态合金中存在着堆垛方式为14H的长周期结构Mg₁₂YZn（X相）,退火以后长周期结构的具体堆垛方式未发生变化,仍然为14H结构。退火球磨的Mg_88.4Y_5.6Zn₆（at.%）合金储氢性能优于铸态球磨的Mg_88.4Y_5.6Zn₆（at.%）合金。在330°C下,两种合金样品都能吸氢超过5wt.%,退火球磨的样品放氢量远远大于铸态球磨的样品。相对应的XRD结果与储氢性能相符合,退火球磨样品PCI后的XRD中不存在MgH2,而铸态球磨样品PCI后的XRD中存在着大量的MgH₂,说明,退火球磨样品在放氢过程中MgH2分解完全,而铸态球磨的样品在放氢过程MgH₂分解不完全。合金中的三个相都吸氢,吸氢后,生成MgH₂、YH₂、YH₃、MgZn相,Mg₁₂YZn（X相）和Mg₃Y₂Zn₃（W相）在吸氢过程中分解。由Mg_88.4Y_5.6Zn₆（at.%）合金的Van’t Hoff曲线可知,该合金吸氢时的标准摩尔焓变已经降低到-65KJ/mol H2,这比MgH2（-74KJ/mol H₂）的标准摩尔焓变已有所下降,但仍不足以从本质上改变其吸放氢困难的问题。该合金的最低放氢温度要高于320°C。吸氢与放氢后的产物中均存在Y的氢化物,说明Y吸氢,但是吸氢后形成的氢化物比较稳定,在放氢过程中难以分解,而在温度稍微高一些的情况下（大于360°C）,MgH₂可以完全分解,因此Mg_88.4Y_5.6Zn₆（at.%）合金的吸放氢循环实质上是Mg与MgH₂之间的循环。更多还原

【Abstract】 Mg-based hydrogen storage materials have relatively high theoretical hydrogen storagecapacity,low cost and abundant resource, however, demerits of high hydriding/dehydridingtemperature, high themodynamic stability and poor kinetic properties hinder their practicalapplication. In this paper, the research and development of Mg-based hydrogen storagematerials were reviewed firstly. On this basis,the hydrogen storage properties andMicrostructures of Mg_88.4Y_5.6Zn₆（at.%） alloy prepared by induction melting were investigatedby using X-ray diffraction（XRD）, scanning electron microscopy（SEM）, energy dispersiveX-ray spectroscopy（EDS）, transmission electron microscopy（TEM）,respectively.Finally, thephases transformation during hydrogenation/dehydrogenation process, the data of basicthermodynamics and hydriding/dehydriding mechanism were obtained.The microstructure of the as-cast alloy was composed of Mg solid solution grains withrather lower alloy elements,Long period stacking ordered （LPSO）phase and the equilibriumand nonequilibrium eutectic.The thick equilibrium and nonequilibrium eutectic microstructurewere Mg and Mg₃Y₂Zn₃ （W） phase.A large number of LPSO phase Mg₁₂YZn（X）, which werelath-like, interconnected to be a net.After 450°C annealing treatment for 48h, themicrostructure became fragmentation without the compositon of phases changed.The thickequilibrium and nonequilibrium eutectic microstructure dissolved and became thin anddiscontinuous shape.LPSO structure also tended to be fragmentation and it’s content reduced.Magnesium solid solution became irregular shape from the origial granular.Ball milling isbenefit for refining the organization, milled samples show particle-like, it’s size is about40μ⁷0μ. The specific structure of LPSO phase Mg₁₂YZn（X phase） in the as-castMg_88.4Y_5.6Zn₆（at.%） alloy is 14H, there were no change for the structure of LPSO afterannealed.The hydrogen storage properties of ball milling alloy after annealing is better thanas-cast ball milling alloy.The hydrogen absorption capacity of as-cast ball milling alloy andannealed ball milling alloy both surpassed 5 wt.% in 330°C, but dehydrogenation content ofannealed ball milling alloy is more higher than as-cast ball milling alloy. There are a lot of MgH₂ in the as-cast ball milling alloy after PCI, on the contrary, there are no MgH₂ in theannealed ball milling alloy after PCI. This show that the MgH₂ in annealed ball milling alloydecomposed in the dehydrogenation process, but the MgH₂ in as-cast ball milling alloy woundnot.Mg, Mg₁₂YZn（X phase） and Mg₃Y₂Zn₃ in alloy all can absorption hydrogen, afterhydrogenation, there will be MgH₂, YH₂, YH₃, MgZn formation, Mg₁₂YZn（X phase） andMg₃Y₂Zn₃（W phase） decomposed. From the Van’t Hoff plot of the Mg_88.4Y_5.6Zn₆（at.%） alloywe know, the standard molar enthalpy of this alloy has been reduced to -65kJ/mol H₂, thisvalue is lower than the standard molar enthalpy of MgH₂ （-74 kJ/mol H₂）. But this alloy isalso difficult to dehydrogenation, actually, below the temperature of 320°C it can not releasehydrogen.MgH₂ can decompose over 330°C but the hydride of Y is very steady and difficultto decompose.So the nature cycle of hydrogenation/dehydrogenation process forMg_88.4Y_5.6Zn₆（at.%） alloy is the shift between Mg and MgH₂.更多还原