Synthesis and dehydrogenation of M(AlH4)2 (M = Mg, Ca)
Synthesis and dehydrogenation of M(AlH4)2 (M = Mg, Ca)
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DOI：
10.1016/j.jallcom.2007.01.119
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发表时间：
2007-10
影响因子：
6.2
通讯作者：
K. Komiya;N. Morisaku;Y. Shinzato;K. Ikeda;S. Orimo;Y. Ohki;K. Tatsumi;H. Yukawa;M. Morinaga
中科院分区：
文献类型：
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作者：
K. Komiya;N. Morisaku;Y. Shinzato;K. Ikeda;S. Orimo;Y. Ohki;K. Tatsumi;H. Yukawa;M. Morinaga
以MgCl 2和NaAlH 4为原料，通过复分解反应合成了Mg（AlH 4）2。它在两步反应中分解，与以前的报告[1]一致。第一个反应是分解形成MgH 2的特征，第二个反应是MgH 2进一步分解成一些铝合金相。当TiCl_3的质量分数为1-5mol%时，可显著降低第一步反应的分解温度。以Mg（AlH_4）_2和5mol%TiCl_3为例，在室温下球磨10.8ks时，有大量的氢释放出来。第一反应的分解温度随试样中TiCl 3含量的增加而降低。然而，再氢化反应几乎没有发生，即使在预分解的含TiCl 3的试样。例如，在353 K下，将1mol%TiCl_3掺杂的试样长时间暴露于30 MPa的氢气氛中，仅0.3mass%的氢被吸收。该结果表明，Mg（AlH 4）2太不稳定而不能顺利进行再氢化反应。因此，接下来选择Ca（AlH 4）2，因为从我们[2]提出的络合物的相稳定性图来看，它似乎比Mg（AlH 4）2更稳定。合成了Ca（AlH 4）2，并对其分解反应进行了初步研究。
Mg(AlH4)2was synthesized by a metathesis reaction of MgCl2and NaAlH4. It was decomposed in the two-step reactions, in agreement with the previous report [1]. The first reaction is characteristic of the decomposition to form MgH2, and the second reaction is the further decomposition of this MgH2into some aluminum alloy phases. The decomposition temperature of the first reaction could be reduced remarkably when it was mixed with 1–5mol% TiCl3. For example, in the case of Mg(AlH4)2mixed with 5mol% TiCl3by ball-milling for 10.8ks, a large portion of hydrogen was released during the milling at ambient temperature. The decomposition temperature of the first reaction decreased with increasing content of TiCl3in the specimen. However, the re-hydrogenation reaction scarcely occurred even in the pre-decomposed TiCl3-containing specimen. For example, only 0.3mass% of hydrogen was absorbed in the 1mol% TiCl3-doped specimen by exposing it for a long period to the hydrogen atmosphere of 30MPa at 353K. This result indicates that Mg(AlH4)2is too unstable to progress the re-hydrogenation reaction smoothly. Therefore, Ca(AlH4)2was chosen next, because this seems more stable than Mg(AlH4)2, judging from the phase stability diagram of complex hydrides proposed by us [2]. Ca(AlH4)2was synthesized and its decomposition reactions were investigated in a fundamental manner.