La-H化合物对LaMg_2Ni合金中Mg_2Ni相吸氢过程的影响(英文)

Effect of La hydride Compound on Hydriding Process of Mg_2Ni Phase in LaMg_2Ni Alloy

采用感应熔炼技术在Ar气氛保护下制备得到LaMg2Ni与Mg2Ni合金。X射线衍射(XRD)图表明LaMg2Ni合金在吸氢过程中分解为LaH3相和Mg2NiH4相,放氢过程中LaH3相转化为La3H7相。与Mg2Ni合金相比,LaMg2Ni合金显示出优良的吸氢动力学性能,这是由于镧氢化合物的存在及其在吸氢过程中所发生的相转变所造成的。LaMg2Ni合金280 s内吸氢即可达到最大储氢量的90%以上,而Mg2Ni合金则需要1200 s才能达到,且在相同温度下LaMg2Ni合金的吸氢反应速率常数大于Mg2Ni合金速率常数。镧氢化合物不仅有利于改善动力学性能,而且可以提高热力学性能。LaMg2Ni合金中的Mg2Ni相氢化反应焓与熵分别为-53.02 kJ.mol-1和84.96 J.K-1.mol-1(H2),这一数值小于单相Mg2Ni氢化反应焓与熵(-64.50 kJ.mol-1,-123.10 J.K-1.mol-1(H2))。压力-组成-温度(P-C-T)测试结果表明在603 K至523 K温度范围内,LaMg2Ni合金储氢容量保持稳定为1.95wt%左右,然而Mg2Ni合金的储氢容量则由4.09wt%衰减为3.13wt%,Mg2Ni合金的储氢容量在523K低温下仅为603 K时的76.5%,表明镧氢化合物能够改善Mg2Ni合金低温下的吸放氢性能。

LaMg2Ni and Mg2Ni alloys were prepared by inductive melting under Ar atmosphere. X-ray diffraction （XRD） shows that during hydrogenation, LaMg2Ni alloy decomposes to LaH3 phase and Mg2NiH4 phase, in dehydriding process this alloy releases H2 and LaH3 phase changes to La3H7 phase. Compared with Mg2Ni alloy, on account of the existence of La hydride compound and phase transition from La3H7 phase to LaH3 phase in hydriding process, LaMg2Ni alloy shows better hydriding kinetics. It is within 280 s for LaMg2Ni alloy to reach 90% of the maximum hydrogen absorption capacity, while it needs 1 200 s for pristine Mg2Ni alloy to do so. The rate constant of LaMg2Ni alloy is larger than that of Mg2Ni alloy at the same temperature. La hydride compound is beneficial not only to the enhancement of hydriding kinetics but also to the improvement of the thermodynamic properties. The enthalpy and entropy for the hydriding Mg2Ni in the LaMg2Ni alloy are -53.02 kJ.mo1-1, 84.96 J. K^1-.mo1-1 （H2）, respectively. Mg2NiH4 in LaMg2Ni alloy is less stable than pristine Mg2Ni alloy （-64.50 kJ. mool^-1 and -123.10 J.K^-1.mol^-1 （H2）. Pressure-Composition- Temperature （P-C-T） measurement results show that the hydrogen storage capacity of LaMg2Ni alloy is about 1.95wt% and is kept stable from 603 K to 523 K, while the hydrogen storage capacity of pristine Mg2Ni alloy declines distinctly form 4.09wt% to 3.13wt% with the reductionof temperature from 603 K to 523 K. The hydrogen storage capacity of pristine Mg2Ni alloy at lower temperature （523 K） is only 76.5% when compared to that at 603 K, suggesting that La hydride compound could improve the hydriding/dehydriding properties of Mg2Ni alloy at low temperature.