Diffusion of H through Pd membranes: Effects of non-ideality
Diffusion of H through Pd membranes: Effects of non-ideality
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DOI：
10.1016/j.memsci.2007.08.032
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发表时间：
2007-12
影响因子：
9.5
通讯作者：
T. Flanagan;Da Wang;K. Shanahan
中科院分区：
文献类型：
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作者：
T. Flanagan;Da Wang;K. Shanahan
H扩散常数DH是从通过Pd膜的稳态通量中获得的，下游侧保持在[公式：见正文] ≤ 0。H通量与（1/d）（其中d为厚度）的关系曲线具有良好的线性，证明在此温度（423- 523 K）和[公式：见正文]范围（≤ 0.2 MPa）内，H渗透受体扩散控制。在恒定的pH值和恒定的H含量下测定了DH值。H通量通过Pd膜与三种不同的表面处理进行了研究（抛光（未氧化），氧化和palladized），以确定这些预处理的效果。钯化和氧化膜给出类似的DH值，但抛光膜给出的值低约12%。对于浓度梯度中的扩散，J=−DH <$（cH/RT）（dμH/dx）是通量的正确方程，其中cHis是H浓度，而不是菲克第一定律，J=−DH（dcH/dx），其中DH和DH <$是依赖于浓度和与浓度无关的扩散常数。用热力学因子[公式：见正文]，从DH中可得到DH δ。在通常采用的情况下，膜的上游侧和下游侧之间的浓度差异很大，热力学因子随通过膜的距离而变化，在获得DH Δ时应考虑到这一点。程序给出并用于确定DH从DH（cH）时，有一个大的浓度梯度通过膜。扩散活化能，艾德（cH），已被确定。ED随着cH的增加而增加，这是热力学因素造成的.
H diffusion constants, DH, have been obtained from steady-state fluxes through Pd membranes with the downstream side maintained at [Formula: see text] ≈0. Good linearity of plots of H flux versus (1/d), where d is the thickness, attests to H permeation being bulk diffusion controlled in this temperature (423–523K) and [Formula: see text] range (≤0.2MPa). DHvalues have been determined at constant pupand also at constant H content. H fluxes through Pd membranes with three different surface treatments have been investigated (polished (unoxidized), oxidized and palladized) in order to determine the effects of these pre-treatments. The palladized and oxidized membranes give similar DHvalues but the polished membranes give values about 12% lower. For diffusion in a concentration gradient J=−DH∗(cH/RT)(dμH/dx) is the proper equation for the flux, where cHis the H concentration, rather than Fick's first law, J=−DH(dcH/dx), where DHand DH∗are the concentration-dependent and -independent diffusion constants. DH∗can be obtained from DHusing the thermodynamic factor, [Formula: see text] . In the commonly employed situation, where there is a large difference in concentrations between the upstream and downstream sides of a membrane, the thermodynamic factor varies with distance through the membrane and this should be allowed for in obtaining DH∗. Procedures are given and utilized to determine DH∗from DH(cH) when there is a large concentration gradient through the membrane. Activation energies for diffusion, ED(cH), have been determined. EDis found to increase with cH, which is attributed to the thermodynamic factor.