| The insulation materials and metal materials in the jacket of high vacuum multilayer insulation cryogenic equipment release H2 for a long time.Therefore,the original vacuum will be deteriorated,and the insulating performance of the equipment will be seriously affected.The placement of getters has become one of the indispensable links in the low-temperature storage and transportation equipment to maintain high vacuum.In this paper,the getters used in the vacuum jacket of cryogenic vessels can be classified into three kinds.The first is chemisorption,which is mainly characterized by chemical reaction between getters and the adsorbates,such as palladium oxide,copper oxide and so on.The second is physical adsorption,which is characterized by getters and adsorbents（generally gas）by van der Waal force adsorbed in the getter micropores,such as molecular sieve,activated carbon,etc.;The third type of getter,which has both chemical reaction and physical adsorption,is common such as silver molecular sieve and silver getter.Traditional PdO is recognized as one of the excellent hydrogen getters.A test platform for the performance of PdO was designed to systematically study the relationships among hydrogen sorption performance,sorption rate,sorption efficiency,sorption capacity and equilibrium pressure of PdO under different orders of pressure.The experimental results defined that the lowest pressure obtained by sorption of PdO was 0.016 Pa,the saturated sorption capacity was 197.2 ml/g,and the sorption coefficient was 60.5.The hydrogen sorption behavior of 31 groups was observed by repeated hydrogen injection at different orders of magnitude of 1 Pa,10-1 Pa and 10-2Pa.The results constructed that the dynamic curves of hydrogen sorption show an"L"shape change under the initial pressure of 2.7 Pa,and the final equilibrium pressures were better than 0.05 Pa.The hydrogen sorption efficiency of first 24 groups exceeded 91%.The experimental results shown that the sorption type of hydrogen getter was consistent with Langmuir model.The X-ray powder diffractogram analysis of PdO after hydrogen sorption showed that,in addition to the elemental Pd,Pd1.5H2and Pd H0.706 were also found after the reaction between PdO and H2,thus increasing the sorption capacity of PdO.The results of this study provide a reference basis for PdO to be applied in cryogenic vessels.However,on account of the high cost of PdO,several novel-fashioned hydrogen getters have been found in the word.Via comprehensively comparing the hydrogen sorption performance of traditional PdO,it has been proved that these novel hydrogen getters have the characteristics of chemical absorption and physical adsorption simultaneously.In this study,the sorption capacity of the novel hydrogen getters was measured by the constant volume method,so as to explore the sorption rate of hydrogen getters,and obtained the sorption isotherm curve of each hydrogen getters.The calculated results showd that the sorption process of the three hydrogen getters is more in line with the first type of BDDT classification,namely Langmuir sorption.The results estimated that the silver getter with more silver carrying capacity is more favorable to the sorption of H2.In this study,BJH and BET methods were used to calculate the specific surface area,pore volume and pore diameter of getters,and the sorption performance was compared.The results demonstrated that the larger the specific surface,the larger the pore volume and the smaller the pore diameter were more favorable to the novel type of hydrogen getter.In addition,this kind of getters has higher cost performance and the manufacturing cost is only～6%of that of PdO.The experimental results provided a basis for the application of the novel-fashioned hydrogen getters in high vacuum multilayer insulation structures.The work focused the novel type of hydrogen getter in low temperature to maintain the performance of the vacuum container on full life cycle research.The manuscript also discussed the domestic and foreign scholars for different getter in the study of the sorption performance of the cryogenic vessels,analyzed the causes of gas in the vacuum jacket,explored the selection of getter,sorption performance and the sorption mechanism,sorption process,put forward the future research direction. |
