Y-Fe基稀土储氢合金的性能研究

发布时间：2018-05-29 11:31

  本文选题：Y-Fe系储氢合金 + YFe_2相　； 参考：《北京有色金属研究总院》2016年硕士论文

【摘要】：本文以YFe_2和YFe_3合金为研究对象,采用XRD、SEM/EPMA、PCT等测试分析方法,研究了A、B侧的元素替代对该体系合金结构及储氢性能的影响规律,以期开发出一种低成本、高性能的非镍基稀土系新型储氢材料。首先,研究了YFe_2合金的结构及储氢性能。铸态合金为多相结构,除主相YFe_2之外,还存在一定量的YFe_3相和Y的氧化物相。第一性原理计算表明,YFe_2相和YFe_3相的自由能十分接近,成分的不均匀和能量起伏,极易导致两相间的转变。热处理提高了YFe_2相的含量,合金初始最大吸氢量可达1.998 wt.%,但经吸放氢循环后,YFe_2相易发生歧化反应,导致合金吸放氢容量下降。A侧Ce对Y的适量替代改善了Y_(1-x)Cex Fe_2合金(x=0,0.15,0.25)的吸放氢动力学性能和循环性稳定性,随着Ce替代量的增多,合金中YFe_3相含量升高,其稳定吸氢容量增大。当Ce的替代量为x=0.25时,合金中YFe_3相含量最多,经7次吸放氢循环后,具有最高的稳定吸氢容量,且合金吸氢动力学性能好,容量衰减最低,具有最好的循环稳定性,但当x增至0.5时,YFe_3相减少,合金的吸放氢循环稳定性降低。在以上基础上,进一步研究了YFe_3合金的结构及吸放氢特性。其铸态合金亦为多相结构,除主相YFe_3相外,还含有较多的Y6Fe_(23)相。经过量添加Y(2 wt.%),并在1100℃退火热处理72小时后,有效提高了合金中的YFe_3相含量,达到75.8 wt.%,降低了合金中YFe_2相含量,提高了合金吸氢循环稳定性,其稳定吸氢容量可达1.433wt.%,但合金吸氢坪台压偏低。为改善YFe_3合金吸氢坪台特性,对YFe_3合金进行B侧元素替代研究;研究发现,YFe_3-xMx(M=Mn,Al)合金吸氢容量随着Mn、Al元素替代量的增加而逐渐减小,吸氢坪台倾斜加剧。对YFe_3合金A侧元素进行元素替代(La、Ce等)。研究发现,La并不能有效替代YFe_3合金中的Y元素,且La以氧化物形式存在,随着La含量的增多,合金吸氢容量及动力学性能逐渐下降,合金吸氢坪台更加倾斜。在Y_(1-x)Cex Fe_3合金(x=0,0.15,0.25和0.5)中,适量的Ce替代,可以有效提高合金的吸氢坪台压力,当Ce替代量为x=0.15和0.25时,合金坪台特性较好。但随着合金中Ce替代量的增加,合金中YFe_2相含量逐渐增多,合金吸放氢循环稳定性降低。同时,Mg元素的少量(x"f0.15)替代并未改善Y_(0.85-x)Mg_xCe_(0.15)Fe_3合金的吸氢坪台特性。综合对比发现,YFe_3相稳定性优于YFe_2相,且合金吸氢量高,适量的Ce替代可以改善YFe_3合金的吸氢坪台特性,但Ce的替代量x应低于0.25。
[Abstract]:In this paper, the effects of element substitution on the structure and hydrogen storage properties of YFe_2 and YFe_3 alloys were studied by means of XRDX SEM / EPMA-PCT and other methods, in order to develop a low cost. High performance non-nickel-based rare earth is a new hydrogen storage material. Firstly, the structure and hydrogen storage properties of YFe_2 alloy were studied. The as-cast alloy has a multiphase structure, in addition to the main phase YFe_2, there are a certain amount of YFe_3 phase and Y oxide phase. The first principle calculation shows that the free energy of YFe2 phase and YFe_3 phase are very close, and the inhomogeneity and energy fluctuation of the composition can easily lead to the transition between the two phases. Heat treatment increases the content of YFe_2 phase, and the initial maximum hydrogen absorption capacity of the alloy can reach 1.998 wt. however, after the cycle of hydrogen absorption and desorption, the phase of YFe2 is easily disproportionated. The hydrogen absorption and desorption kinetic properties and cyclic stability of Y_(1-x)Cex Fe_2 alloy were improved due to the decrease of hydrogen absorption and desorption capacity. The content of YFe_3 phase increased and the stable hydrogen absorption capacity increased with the increase of ce substitution. When the substitution amount of ce is x0. 25, the content of YFe_3 phase in the alloy is the highest. After 7 cycles of hydrogen absorption and desorption, the alloy has the highest stable hydrogen absorption capacity, and its hydrogen absorption kinetic property is good, the capacity attenuation is the lowest, and the alloy has the best cycle stability. However, when x increases to 0.5, the phase of YFe3 decreases and the cycle stability of hydrogen absorption and desorption decreases. On the basis of above, the structure and hydrogen absorption and desorption properties of YFe_3 alloy were further studied. The as-cast alloy also has a multiphase structure. In addition to the main phase YFe_3 phase, it also contains more Y _ 6Fe _ 2O _ 3) phases. After annealing at 1100 鈩，

本文编号：1950728