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首页> 外文期刊>Journal of Alloys and Compounds: An Interdisciplinary Journal of Materials Science and Solid-state Chemistry and Physics >Theoretical and experimental study on Mg(BH_4)_2-Zn(BH_4)_2 mixed borohydrides
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Theoretical and experimental study on Mg(BH_4)_2-Zn(BH_4)_2 mixed borohydrides

机译：Mg（BH_4）_2-Zn（BH_4）_2混合硼氢化物的理论和实验研究

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After a screening of possible systems prone to give an enthalpy of decomposition close to 30 kJ mol~(H2)~(-1), i.e. suitable for a dehydrogenation process close to room temperature and pressure, the Zn dissolution into Mg(BH_4)_2 has been investigated. The total energy of pure compounds and solid solutions has been computed by DFT calculations using the CRYSTAL09 code. To generate the Mg_(1-x)Zn_x(BH_4)_2 solid solution, α-phase of Mg(BH_4)_2 (space group P6_122) has been considered, with a replacement of Mg~(2+) with Zn~(2+) ions, without lowering the symmetry of the crystalline structure. On the basis of DFT results, the enthalpy of decomposition has been estimated, considering MgH_2, Zn, α-B and H_2 as products, and a value of 30 kJ mol~(H2)~(-1) has been calculated for x = 0.2. In order to verify the results of calculations, mixtures of Mg(BH_4)_2 and ZnCl_2 with 1.0:0.7 ratio have been ball milled, both at room temperature and in cryo-condi-tions. Samples have been analyzed with a combination of experimental techniques (XRD, DSC, IR-ATR, TGA, TPD, PCI). The phase mixture obtained after the synthesis strongly depends on the milling conditions. For prolonged times, the formation of Zn and MgCl_2 has been observed, suggesting the delivering of B-contain-ing species during the milling. After heating, a hydrogen release, coupled with diborane delivering, has been observed for temperatures close to 100 °C, suggesting a significant decrease of the decomposition temperature with respect to pure Mg(BH_4)_2. Theoretical and experimental results have been discussed on the basis of the possible reaction paths, as estimated from available thermodynamic databases.
机译：在筛选出可能产生接近30 kJ mol〜（H2）〜（-1）的分解焓后，即适合在接近室温和压力的脱氢过程中，Zn溶解成Mg（BH_4）_2已被调查。通过使用CRYSTAL09代码进行DFT计算，可以计算出纯化合物和固溶体的总能量。为了生成Mg_（1-x）Zn_x（BH_4）_2固溶体，已经考虑了Mg（BH_4）_2（空间群P6_122）的α相，并用Zn〜（2）代替了Mg〜（2+）。 +）离子，而不会降低晶体结构的对称性。根据DFT结果，以MgH_2，Zn，α-B和H_2为产物估算了分解的焓，对于x = 30 kJ mol〜（H2）〜（-1）。 0.2。为了验证计算结果，无论是在室温下还是在低温条件下，均已球磨了Mg（BH_4）_2和ZnCl_2的混合物，其比例为1.0：0.7。样品已通过实验技术（XRD，DSC，IR-ATR，TGA，TPD，PCI）的组合进行了分析。合成后获得的相混合物很大程度上取决于研磨条件。长时间以来，观察到了Zn和MgCl_2的形成，这表明在研磨过程中会释放出含B的物质。加热后，在接近100°C的温度下观察到有氢气释放和乙硼烷释放，表明分解温度相对于纯Mg（BH_4）_2明显降低。已根据可能的反应路径对理论和实验结果进行了讨论，并根据可用的热力学数据库进行了估算。

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