| Summary: | 碩士 === 國立中央大學 === 材料科學與工程研究所 === 102 === In this study, the preparation and modification of PdAg membrane used for H2 separation has been studied. The PdAg membranes are deposited on the modified Ag substrate by various electroless plating methods, including conventional electroless co-plating (C-ELCP), successive electroless plating (S-ELP), and Ag-controlled electroless co-plating (Ag-ELCP). The morphologies, surface function groups, and structures of the prepared Ag substrates and PdAg membranes are analyzed by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD), respectively.
The porous Ag substrates with surface modification of Pd70Ag30 nanoparticles are used to support the membrane. Ag powders are coated by SA or PVP, which are confirmed by Fourier transform infrared spectroscopy (FTIR). Afterwards, Ag-SA and Ag-PVP powders are mechanically pressed at 1500 psi for 3 min, and heat-treated at 350 oC for 1 h in air to get porous Ag substrates. By filling with Pd70Ag30 nanoparticles, the pore size has decreased and the surface becomes smooth.
SEM observation reveals that a uniform and dense PdAg membrane can be prepared by C-ELP at 400 rpm of stirring rate on Ag-PVP substrate. However, even the ratio of Pd/Ag in plating bath is up to 90/10, the Pd composition on the Ag-PVP substrate is only 37.6 %. On the other hand, when prepared by S-ELP method, it is found that desired Pd/Ag ratio of 70/30 with separated Ag, Pd, and PdAg phases of the membrane can be obtained. After heat treatment at various atmospheres, it is noted that air heat treatment results in the oxidation of Pd. However, N2 and H2 treatments can promote the formation of PdAg alloy phase. For the membrane prepared by Ag-CLCP, a membrane with the most uniform and dense structure can be prepared. During heat treatment, Pd composition decrease and the membrane become denser with increasing heat treatment time. The SEM line-scan results reveal that the Pd content is in the range of 60 and 80 at% for as-prepared C-Pd70. After heat treatment for 15 h, the Pd composition drops to 20~30 at % due to significant Ag segregation from the substrate during long-term heat treatment.
The corresponding permeation fluxes of H2 at various pressures follow a linear relationship, suggesting that Sievert’s law is not obeyed in the PdAg membranes and the permeation rate is dominant by surface-reaction-controlled process. The H2/N2 selectivity is about 3 for C-Pd70 sample prepared by Ag-ELCP method because of the formation of micrometer-scaled hillocks and pinholes which declines the selectively.
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