Department of Imaging and Applied Physics, Curtin University of Technology, GPO Box U 1987, Perth WA 6845, Australia.
J Am Chem Soc. 2010 Apr 14;132(14):5077-83. doi: 10.1021/ja908398u.
The thermodynamic properties of magnesium hydride nanoparticles have been investigated by hydrogen decomposition pressure measurements using the Sieverts technique. A mechanochemical method was used to synthesize MgH(2) nanoparticles (down to approximately 7 nm in size) embedded in a LiCl salt matrix. In comparison to bulk MgH(2), the mechanochemically produced MgH(2) with the smallest particle size showed a small but measurable decrease in the decomposition reaction enthalpy (DeltaH decrease of 2.84 kJ/mol H(2) from DeltaH(bulk) = 74.06 +/- 0.42 kJ/mol H(2) to DeltaH(nano) = 71.22 +/- 0.49 kJ/mol H(2)). The reduction in DeltaH matches theoretical predictions and was also coupled with a similar reduction in reaction entropy (DeltaS decrease of 3.8 J/mol H(2)/K from DeltaS(bulk) = 133.4 +/- 0.7 J/mol H(2)/K to DeltaS(nano) = 129.6 +/- 0.8 J/mol H(2)/K). The thermodynamic changes in the MgH(2) nanoparticle system correspond to a drop in the 1 bar hydrogen equilibrium temperature (T(1 bar)) by approximately 6 degrees C to 276.2 +/- 2.4 degrees C in contrast to the bulk MgH(2) system at 281.8 +/- 2.2 degrees C. The reduction in the desorption temperature is less than that expected from theoretical studies due to the decrease in DeltaS that acts to partially counteract the effect from the change in DeltaH.
采用 Sieverts 技术通过氢分解压力测量研究了氢化镁纳米粒子的热力学性质。采用机械化学方法合成了嵌入 LiCl 盐基体中的 MgH(2)纳米粒子（尺寸约为 7nm）。与体相 MgH(2)相比，具有最小粒径的机械化学合成的 MgH(2)表现出分解反应焓略有降低（DeltaH 从体相的 74.06 +/- 0.42 kJ/mol H(2)降低至纳米相的 71.22 +/- 0.49 kJ/mol H(2)，降低了 2.84 kJ/mol H(2)）。DeltaH 的降低与理论预测相符，并且与反应熵的类似降低相关（DeltaS 从体相的 133.4 +/- 0.7 J/mol H(2)/K 降低至纳米相的 129.6 +/- 0.8 J/mol H(2)/K，降低了 3.8 J/mol H(2)/K）。MgH(2)纳米粒子体系中的热力学变化对应于 1 巴氢气平衡温度（T(1 bar)）降低约 6°C，降至 276.2 +/- 2.4°C，而体相 MgH(2)体系为 281.8 +/- 2.2°C。解吸温度的降低小于理论研究预期的降低，这是由于 DeltaS 的降低部分抵消了 DeltaH 变化的影响。
