Study On Synthesis, Characterization And Properties Of Palladium/Polymer Composite Membrane

Palladium has unique hydrogen-electivity. However, palladium membrane is crisp, poor machinable and costly. Compared to palladium membrane, palladium/polymer composite membrane has many advantages, such as longer life, better hydrogen permeation and lower cost. Furthermore, polymer membrane is helpful to suppress α-toβ-phase transition and to avoid distortion. Palladium/polymer composite membrane not only has traits of palladium and polymer membrane, but also has series of unique characters. So, palladium/polymer composite membrane can be widely used as membrane reactor to hydrogenize and dehydrogenize or to purify and separate gas, as well as hydrogen sensor to in-situ inspect the concentration of hydrogen in surrounding. By controlling self-catalysis or decomposing metastable metallic salt, metal film can be formed on the substrate. This is referred as electroless plating. By traditional electroless plating, metal is mainly deposited on the surface of membrane, just little in the pore of polymer membrane. This results in poor binding force between metal film and the substrate. Combining the characteristics of electroless plating and in-situ permeating, this paper brought forward in-situ permeating electroless plating. By this method, palladium was in-situ deposited in the pore, the distribution of palladium could be controlled by the ordered pores. Consequently, palladium/polymer composite membrane prepared by the new method has better microstructure and binding force. Some factors influencing the microstructure and performance of palladium/polymer composite membrane. The concentration of PdCl₂, Na₂EDTA, NH₃·H₂O, N₂H₄·H₂O and temperature, reaction time were investigated. With depositing rate of palladium as criteria, optimum condition was gotten through experiments. The influence of pore size to microstructure and performance of palladium/polymer composite membrane was discussed and properly explained. Furthermore, the mechanism of in-situ permeating electroless plating was also investigated. DSC results showed that Pd/PTFE composite membrane should be treated at 250℃. At 250℃, Pd/PTFE composite membrane was also stable. However, Pd/PTFE composite membrane began to distort above 250℃and decompose at 300℃. XRD results made sure that there was no impurity in the deposited palladium film and the size of palladium crystalline was less than 20nm. Meanwhile, Pd/PTFE composite membrane, made by in-situ permeating electroless plating, was observed by SEM. The palladium film was made up by even spherules, and its superficial microstructure was better than which made by traditional electroless plating. The experimental results of pore structure, cross-sectional resistivity and binding force showed that by the new method, palladium was mainly deposited in pores, its cross-sectional resistivity reduced largely, and its binding force was improved. The hydrogen sensitivity of Pd/PTFE composite membrane was tested elementally. The different sensitivity of Pd/PTFE composite membrane to hydrogen and nitrogen and its repeatability were discussed. The results showed that Pd/PTFE composite membrane had certain sensitivity to hydrogen. Pd/PTFE composite membrane also has good repeatability. Even exposed to pure hydrogen many times, Pd/PTFE composite membrane did not delaminate and blister. The experiment about hydrogen sensitivity is helpful to take an ulterior investigation.