Si对LaNi5相关系与贮H2性能的影响

本文用X射线多晶衍射方法和差热分析方法研究了LaNi_5-xSi_x(x≤1.25)的相关系,用排水取气法测量了样品的吸H₂性能,LaNi₅,的固溶体和新的三元化合物LaNi₄Si形成共晶体系,共晶温度1170℃,共晶点x=0.96,在单相区中LaNi₅,相点阵常数随Si替代量增加,a减小,c增大,三元化合物LaNi₄Si属正交晶系,点阵常数a=8.382?,b=5.210?,c=3.989?。测量密度D₀=7.59g/cm³,每单胞含两个化合式单位,可能的空间群为D_2h⁵,C_2v²和C_2v⁴,它具有可逆的吸放H₂性能,吸H₂后形成氢化物LaNi₄SiH_3.6。La_1-ySi_yNi,系列样品吸H₂量随Si含量增加而很快下降,LaNi_5-xSi_x系列样品吸H₂量随Si含量的增加稍略下降,平台压力也下降,LaNi_4.8Si_0.2的生成自由能为476cal/molH₂,固溶体氢化物的稳定性比LaNi₁高。 关键词：

THE INFLUENCE OF Si ON PHASE RELATION AND HYDROGEN ABSORPTION PROPERTIES OF LaNi5

In this work, the phase relations of LaNi_5-xSi_x(x≤1.25) have been studied by means of X-ray powder diffraction method and DTA method, and the hydrogen absorption properties of the samples have been measured using gas-gathering method. The α-phase (LaNi₅) and the new discovered ternary compound LaNi₄Si (β) forms a eutectic system. The eutectic reactionis α+β(?)1170℃/ L. The eutectic point is at x=0.96. In the single phase area of a-phase, the lattice parameter a de-creases and c increases with the substitution of Si, The ternary compound LaNi₄Si belongs to orthorhqmbic system with lattice parameters a = 8.382?, b = 5.210?, c = 3.989?. The measured density is 7.59 g/cm³. There are two formula unit per unit cell. Possible space groups are D_2h⁵,C_2v²,C_2v⁴. The hydrogen quantities absorbed by the La_1-ySi_yNi₅ samples decrease rapidly with Si content increasing. The absorbed hydrogen quantities of La-Ni_5-xSi_x samples vary slowly with the Si content and the plateau pressures decrease. The formation free energy of LaNi_4.8Si_0.2H_6.5 is 475 cal/mol H₂. Si substitution increased the stability of hydrides. The new compound LaNi₄Si has reversible hydrogen absorption and desorption properties with formation of hydride LaNi₄SiH_3.6.
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