Fast lateral hydrogen diffusion in magnesium-hydride films on sapphire substrates studied by electrochemical hydrogenography
Fast lateral hydrogen diffusion in magnesium-hydride films on sapphire substrates studied by electrochemical hydrogenography
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DOI：
10.1016/j.ijhydene.2017.11.101
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发表时间：
2018-01
影响因子：
7.2
通讯作者：
N. Teichmann;M. Hamm;A. Pundt
中科院分区：
文献类型：
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作者：
N. Teichmann;M. Hamm;A. Pundt
氢在镁薄膜中的横向膜方向的扩散研究逐步电化学加载通过在二氢化物形成过程中的光传输（电化学氢谱法）的变化。在第一加载步骤期间，二氢化物前沿传播动力学允许通过应用分析模型以及替代地通过与有限元模拟进行比较来确定膜中的横向氢扩散系数。随后的加载步骤显示二氢化物前沿传播的时滞行为。因此，它们可以被视为渗透实验。这些随后的加载步骤可以通过氢沿沿着晶界扩散和通过考虑晶界中氢位能量分布的高斯形状来解释。平均而言，横向薄膜方向的有效氢扩散系数为3− 2+ 12 <$10 − 12 m 2 s。该值是在室温下氢在Mg-二氢化物中扩散的已知最高值。这种高的横向氢扩散率的可能来源进行了讨论，包括优先氢扩散沿着的Mg/Mg-氧化物界面，各向异性的扩散系数和各向异性膜膨胀后的扩散能垒降低。
Hydrogen diffusion in thin magnesium films in lateral film direction is studied by stepwise electrochemical loading via the change in optical light transmission (‘electrochemical hydrogenography’) during the dihydride formation. During the first loading step, the dihydride front propagation kinetics allows determining the lateral hydrogen diffusion coefficient in the film, by applying an analytical model and, alternatively, by comparison with finite-element simulations. Subsequent loading steps show a time lag behavior in the dihydride front propagation. Therefore, they can be regarded as permeation experiments. These subsequent loading steps can be explained by hydrogen diffusion along grain boundaries and by taking the Gaussian shape of the hydrogen site energy distribution in the grain boundaries into account. In average, an effective hydrogen diffusion coefficient of 3− 2+ 12⋅ 10− 12 m 2 s was found in lateral film direction. This value is the highest value known for hydrogen diffusion in Mg-dihydride, at room temperature. Possible sources for this high lateral hydrogen diffusivity are discussed including preferential hydrogen diffusion along the Mg/Mg-oxide interface, anisotropy of diffusion coefficients and lowering of diffusion energy barrier upon anisotropic film expansion.