| Palladium and its alloy have been widely used in hydrogen purification owing to their extremely high hydrogen permselectivity. In ITER(International Thermalnuclear Experimental Ractor) fuel cycle system, some impurity gases such as He, CO. CO2, NO3and CQ4(Q=H, D, T) are also deliveried from the plasma besides the unreacted deuterium and tritium gases. Permeation by palladium alloy membrane is the best way to remove them from the fuel gases. However, whether and how the impurity gases influence the hydrogen permeability is still unknown. The effect of CO2and CH4with different ratio on hydrogen permeation through Pd8Y0.23Ru alloy membrane was examined in this thesis at temperature between300℃and450℃.Hydrogen permeation through a Pd8Y0.23Ru alloy membrane at450℃was investigated. At the beginning, hydrogen permeability increased rapidly with the experiment duration, and it gradually came to be stable after20h.The surface composition, morphology and phase structure were studied by XPS, SEM and XRD. The results showed that there were two factors which caused the increase of hydrogen permeability:1) hydrogen permeation removed the carbonaceous impurities on the surface of Pd8Y0.23Ru alloy membrane, which increased the speed of hydrogen gas dissociation and changed the rate-determining step to bulk diffusion of hydrogen atom, and remarkably increased the hydrogen permeability at beginning of experiment2) recrystallization happened during the permeation test, which made the crystal grains smaller, and increased the ratio of grain boundary diffusion resulting in a bigger bulk diffusion coefficient.Hydrogen permeation through a Pd8Y0.23Ru alloy membrane at300℃～450℃was investigated in the presence of CO2. The results showed that the hydrogen permeability was greatly decreased by CO2addition, the higher the CO2concentration was, the more significant the reduction of hydrogen permeation would be. The negative effects of CO2on hydrogen permeation were caused by three factors:(Ⅰ)for higher concentration of CO2(>3%),mass transfer of hydrogen was blocked by CO2barrier layer near the membrane surface, which was the main reason for hydrogen permeation reduction (Ⅱ) while for lower ones(<1%), the main reason was the effects of CO2adsorbing on the membrane and occupying active dissociation sites of hydrogen(Ⅲ) the coexisting CO2gas had poisoning effect on Pd-Y-Ru alloy membrane with the permeation duration, and the poison effect at450℃is stronger than at300℃ Hydrogen permeability was also reduced when CH4is coexisting. The reduction became lager when the CH4concentration was increasing, but the reduction was smaller than coexisting CO2with the same ratio and at the same permeation temperature. Mass transfer of hydrogen blocked by CH4barrier layer near the membrane surface was the main reason for hydrogen permeation reduction when CH4concentration ranged from0.5%to4%. The results also indicated that CH4has no poisoning effect on Pd8Y0.23Ru alloy membrane. |
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