Tritium Aging Effects Of Palladium Hydride Hydrogen Deuterium Exchange Behavior

Due to some excellent properties,such as resistance to oxidation and poisoning,wide plateau of pressure-composition isotherms,remarkable hydrogen isotope effect,easy to activation,fast rate of hydrogen absorption and desorption,fast rate of hydrogen isotope exchange,palladium is widely applied in tritium process.By taking advantage of hydrogen isotope exchange in palladium hydride powder,hydrogen isotope separation,tritium unloading without heating and fast hydrogen isotope displacement can be carried out.How are the applied properties of palladium after tritium aging? Some literatures have reported the following results.Modifications of pressure-composition isotherms are observed: decrease of plateau pressure,increases of plateau slope and tritium heel,also,the mechanical properties decline.The accumulating of decay product ³He in palladium and the forming of Helium bubbles leads to lattice swelling.The defects,such as clusters of self-interstitial, dislocations,dislocation loops appear.What we care in engineering application are whether there are effects in hydrogen isotope exchange in palladium hydride after tritium aging and how are the effects,because their applied properties may change after tritium aging,but there are no literatures reported about aging effects in hydrogen isotope exchange.In order to research the tritium aging effects about hydrogen isotope exchange properties of palladium hydride,the hydrogen-deuterium exchange experiments using palladium powder packed column are carried out.The packing material are 40～60 mesh sponge palladium powder and tritium aging time are 0,1.6 and 3.5 years respectively.The column was saturated with deuterium at first.Then hydrogen was used to exchange the deuterium from one end of the column.By changing the temperture and gas flow,a series of breakthrough curves can be obtained.The changes of the curves for different material are different when there are tritium aging effects.The results of XRD inspection for palladium samples are:peaks go wider and lower,and shift to smaller 20 angle after tritium aging,it indicates that palladium lattice swells.The lattice constant of virgin palladium is 3.8900(?),after 1.6 and 3.5 years aging,they are increased by 0.095%and 0.11%,and become 3.8937(?) and 3.8943(?) separately.In TEM images of palladium samples,obvious helium bubbles can be observed.The results of Hydrogen-deuterium exchange experiment:exchange can reach equilibrium in the gas flow range(0.38～1.96L·cm^-2·min^-1) in virgin palladium hydride powder, so the variances of gas flow have no influence on the exchange performance.The exchange experiments in 0℃,24℃and 50℃indicates that exchange efficiency increase with the increasing of temperature.Because after temperature increased,the energy of hydrogen isotope atoms or molecular improve,their movement rate quicken,the exchange probability and the exchange rate between hydrogen isotope atoms or molecular raise,their diffusion rate in palladium also quicken,so the exchange performance improve.But comparing with tritium aging palladium,the sensitivity to temperature change of exchange performance of virgin palladium is smaller.Because of the positive isotope effect of palladium hydrides,the performance of hydrogen-deuterium exchange is better than deuterium-hydrogen exchange.After tritium aging,the efficiency of hydrogen isotope exchange in palladium hydride powder decline with the aging time increasing,when reach to the same exchange efficiency, the hydrogen quantity employed in exchange increase.Because decay product ³He accumulates and forms helium bubbles in aged palladium,hydrogen isotope is deeply arrested in helium bubbles,so the exchange probability and the exchange rate between hydrogen isotope atoms or molecular descend,their diffusion rate in palladium also descend, so the exchange performance decline.The experiments carried out in 3.5 years aged palladium at same gas flow and different temperatures indicate that the exchange performance of aged palladium is more sensitive to temperature change than virgin palladium.Under the condition of hydrogen isotope separation by displacement chromatography, after tritium aging,the transition zone and the tail zone of the breakthrough curve broaden, the width of the transition zone of 1.6 and 3.5 years aged palladium is 1.5 and 2 times than the one of virgin palladium,the performance of hydrogen isotope separation decline,the quantity of the pure output gas gained from the end of the chromatography column decrease. Under the condition of fast hydrogen isotope displacement,the dispalacement efficiency descends after tritium aging.At the same 99%diapalacement efficiency at invariable gas flow displacement,the hydrogen quantity employed in displacement increase,after 1.6 and 3.5 years aged,they are increased by 7.7%and 23%.