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首页> 外文学位 >Characterization and Modeling of Hydrogen Diffusion in Palladium-Coated Niobium Trilayer Membranes by Electrochemical Permeation Techniques.
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Characterization and Modeling of Hydrogen Diffusion in Palladium-Coated Niobium Trilayer Membranes by Electrochemical Permeation Techniques.

机译：电化学渗透技术表征钯包覆的铌三层膜中氢的扩散和建模。

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摘要

Hydrogen purification membranes are traditionally made from pure Pd and its alloys because these materials offer high throughputs while remaining 100% selective and catalyzing the dissociation/recombination reactions at the surface. However, the high cost of Pd has necessitated the development of newer, cheaper purification systems. The Group V refractory metals Ta, Nb, and V promise even higher permeability at a lower cost, but they are susceptible to forming oxide layers that are impervious to hydrogen. One proposed solution has been to remove these surface layers and apply thin, protective coatings of Pd to form a metallic triple layer.;The electrochemical permeation technique was used to study hydrogen transport through pure Pd, Pd-Ag, and Nb substrates coated with Pd or Pd-Ag. A multilayer diffusion model was developed, in accordance with conditions of the experiments, which can extend to any n-layered system and account for general non-equilibrium interface conditions. Exact solutions were obtained in the Laplace domain and inverted numerically using an appropriate algorithm.;Graphical representations of concentration or flux were produced for various example systems to demonstrate multilayer phenomena associated with different surface conditions or with changes in relative layer thickness, diffusivity, and solubility. A discussion on the effects of non-equilibrium includes further graphical examples and focuses on the deviations from equilibrium behavior.;The time lag tL for a general triple layer with non-equilibrium interfaces is derived completely. The significance of each term is discussed, and special limiting forms of tL are obtained and their physical implications are explained. It is also shown how tL can be attained simply from knowledge of F(s). Parametric analyses are performed with respect to both the time lag tL and the breakthrough time tb, the latter having no analytical form for multilayered systems to this point. Expressions for tb in a symmetric triple layer are derived that are accurate in certain parametric regions. These regions are evaluated through an error analysis comparing the analytical tb with the single layer approximation and the exact value, which shows that Pd/Nb is a system for which the analytical formula applies. Formulas for non-equilibrium cases are developed and discussed as well.;Experimental data from Pd/Nb/Pd specimens is described well by the equilibrium model. Calculated values of k for Pd/Nb are in agreement with theory and past studies. Since k = KPd/KNb 1 and DPd DNb, the downstream Pd layer has a barrier effect that causes accumulation in the Nb layer. The overall process is not diffusion-limited with respect to Nb, so D Nb is not evaluable from tL or the full transient. DNb was instead determined from the breakthrough time tb and was consistent with previously reported values. Results suggest that the equilibrium assumption was valid at the interfaces and that bulk behavior was observed. The results are discussed in the context of some common concerns regarding metallic composites, including: anomalous behavior in thin films, presence of discrete intermixing layers at the interfaces, and interface disturbances resulting from non-equilibrium conditions.
机译：氢纯化膜传统上由纯Pd及其合金制成，因为这些材料可提供高通量，同时仍保持100％的选择性并催化表面的解离/重组反应。但是，Pd的高成本使得必须开发更新，更便宜的纯化系统。 V族难熔金属Ta，Nb和V承诺以更低的成本具有更高的渗透性，但它们易于形成不透氢的氧化物层。一种建议的解决方案是去除这些表面层并涂上一层薄的Pd保护层以形成金属三层。;电化学渗透技术用于研究氢在纯Pd，Pd-Ag和Nb涂覆Pd的基底上的传输或Pd-Ag。根据实验条件，开发了一种多层扩散模型，该模型可以扩展到任何n层系统，并可以解释一般的非平衡界面条件。在Laplace域中获得了精确的溶液，并使用适当的算法对其进行了数值反演；为各种示例系统生成了浓度或通量的图形表示，以证明与不同表面条件或相对层厚度，扩散率和溶解度变化有关的多层现象。关于非平衡影响的讨论包括更多的图形示例，并着重于与平衡行为的偏差。完全推导了具有非平衡界面的一般三层的时滞tL。讨论了每个术语的意义，并获得了tL的特殊限制形式并解释了其物理含义。还显示了如何仅根据F（s）的知识即可获得tL。针对时滞tL和突破时间tb均进行了参数分析，到目前为止，穿透时间tb对于多层系统尚无分析形式。推导出对称三层中的tb表达式在某些参数区域中是准确的。通过将分析的tb与单层近似值和精确值进行比较，通过误差分析来评估这些区域，这表明Pd / Nb是应用分析公式的系统。还开发和讨论了非平衡情况下的公式。通过平衡模型很好地描述了Pd / Nb / Pd样品的实验数据。 Pd / Nb的k计算值与理论和过去的研究一致。由于k = KPd / KNb 1且DPd

著录项

  • 作者

    Wojcik, Garrett.;

  • 作者单位

    Tufts University.;

  • 授予单位 Tufts University.;
  • 学科 Engineering Chemical.
  • 学位 M.S.
  • 年度 2011
  • 页码 295 p.
  • 总页数 295
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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