Mechanical alloying and hydrogen absorption properties of the Mg–Ni system
Mechanical alloying and hydrogen absorption properties of the Mg–Ni system
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DOI：
10.1016/s0925-8388(97)00533-1
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发表时间：
1998-03
影响因子：
6.2
通讯作者：
G. Liang;S. Boily;J. Huot;A. Neste;R. Schulz
中科院分区：
文献类型：
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作者：
G. Liang;S. Boily;J. Huot;A. Neste;R. Schulz
研究了混合元素镁、镍的机械合金化过程。球磨后发现，在x>；66.67时，−x为镁和镁的混合物，x=66.67时为单一的镁镍相。球磨状态下的镁和镁镍的微晶尺寸分别为20和10 nm。当加热到673K时，镁镍保持了其纳米晶结构，而镁+镁镍复合材料中的镁颗粒随退火温度的升高而更快地长大。对这些纳米晶粉末的储氢性能进行了表征。在第一次吸收循环中，我们观察到纳米晶Mg2Ni比两相材料吸氢更快。然而，活化后的纳米晶镁镍在低温(423K)下比纳米晶镁镍具有更好的氢化动力学。这与在传统的粗粒度系统中观察到的情况相反。可能的解释是，镁镍催化了氢在复合材料中的化学吸附，并且相界促进了氢的扩散。用Van‘t Hoff图计算了镁和镁镍的吸附和脱附热。与多晶材料相比，多晶材料的解吸热略有增加，吸附热有所降低。
The mechanical alloying process of mixed elemental Mg and Ni was investigated. After milling, we found a mixture of Mg and Mg2Ni in the composition range x>66.67 for MgxNi100−xand a single Mg2Ni phase at the composition x=66.67. The crystallite sizes of Mg and Mg2Ni in the as-milled state were 20 and 10 nm, respectively. The Mg2Ni keeps its nanocrystalline structure when heated to 673 K, whilst Mg grains in the Mg+Mg2Ni composite grow much more rapidly with increasing annealing temperature. The hydrogen storage properties of these nanocrystalline powders were characterized. During the first absorption cycle, we observed that nanocrystalline Mg2Ni absorbs hydrogen more rapidly than the two-phase material. However, after activation, the nanocrystalline Mg+Mg2Ni has better hydriding kinetics at low temperature (423 K) than nanocrystalline Mg2Ni. This is contrary to what was observed in conventional coarse-grained systems. Possible explanations would be that Mg2Ni catalyses the hydrogen chemisorption in the composite and that the phase boundaries enhance hydrogen diffusion. The absorption and desorption enthalpies of Mg and Mg2Ni were evaluated by Van't Hoff plots. The desorption enthalpy increases a little and the absorption enthalpy decreases compared to polycrystalline materials.