| Energy is an important material basis for the development of today’s economic society. With the development of economic society energy consumption continues to grow. The traditional fossil energy’s massive mining and utilization cause the air pollution and the ecological environment destruction. As a clean energy, the nuclear power does not produce acid rain and greenhouse gas. It is an efficient way to increase the energy supply, optimize the energy structure, fight against climate change and pursue low carbon growth. The research on the thorium-based molten salt reactor(TMSR) system is one of the strategic priority research programs of the Chinese academy of sciences. Its research goal is to develop the fourth generation of fission reactor nuclear energy system. Different from other type of nuclear power systems, however, TMSR in running processes will generate large amount of tritium, because lithium and beryllium in the molten salt absorb neutrons besides boron in the control system.Tritium is a β radioactive isotope of hydrogen. It is an important resource and widely used on the national defense science and technology and the national economy. On the other hand, tritium is radioactive nuclide. The tritium from TMSR will pollute environment and harm human health if it directly emits into the environment. Therefore, it is necessary to recover and store the tritium from TMSR.Solid state storage of tritium in the form of metal tritides is considered as a safer method than other methods. Thus, some hydrogen storage alloys have been successfully applied to recover and store tritium. Among these hydrogen storage alloys, ZrCo alloy has some advantages comparable to those of uranium. It was used as an important candidate material for deuterium/tritium storage in fuel cycle system of ITER project in recent years. But there is a defect in the application of ZrCo alloy, which its operating temperature must be controlled below 400℃. Otherwise the release of tritium in the alloy will be difficult due to disproportionation reaction. LaNi4.25Al0.75 is a kind of hydrogen storage alloy that can be used as a long-term tritium storage alloy. It has some fine properties of resistance to disproportionation and poisoning and fixing helium. Thus, it has widely application prospect. But its plateau pressure at room temperature is higher than uranium. For many years, researchers are focus on the tritium storage alloys with low plateau pressure at room temperature, tritium desorption under milder conditions and large storage capacity. Therefore, it is important to research on improving propertities of these alloys in order to recover and store tritium from TMSR. Tritium is a radioactive gas. Most experiments related to development of tritium storage materials are primarily carried out using hydrogen and deuterium. Owing to the similar chemical properties, reactions of hydrogen isotopes with alloys form their corresponding hydrides, deuterides and tritides with same stoichiometry. As an alternative to tritium, therefore, hydrogen was used to study on the tritium storage properties of alloys in this study.An elemental substitute method was applied in this work. Mg partially substituted La in LaNi4.25Al0.75 alloy. Cu, Cr, Mn and Al partially substituted Co in ZrCo alloy. The effects of alloying elements on the characteristics of phase structure and hydrogen storage propertities of the LaNi4.25Al0.75-based and Zr Co-based alloys were carefully studied by X-ray diffraction(XRD), scanning electron microscope(SEM), differential scanning calorimeter(DSC), inductively coupled plasma optical emission spectrometry(ICP-OES) and the hydrogen absorption/desorption test apparatuses. The hydriding-dehydriding test apparatus with low-pressure capability was designed and established in order to test the hydrogen storage performance of the ZrCo-based alloys. The test apparatus was carefully calibrated before use. The main outcomes of this work are as follows,The as-cast La(1-x)MgxNi4.25Al0.75 alloys(x=0.0, 0.1, 0.2, 0.3) were prepared by an electromagnetic induction melting furnace with a cold crucible. The alloys showed single phase LaNi4 Al with CaCu5 type structure when x=0.0 and 0.1. However, for x=0.2 and 0.3, second phases with PuNi3 and AuCu3 type structures occurred in the alloys, and the abundance of the second phase increased with the rise of x value. The cell volume of main phase LaNi4 Al decreased with the increasing Mg content. There is only one plateau in the alloys. With the increasing of Mg, the plateau pressure of the alloys raised and their hydrogen storage capacity decreased. The degradation of hydrogen storage capacity was mainly due to by the increment of AlNi3 phase abundance. The rate-controlling step was diffusion for the alloys. With the increment of Mg content from 0.1 to 0.3, the absorption kinetics of the alloys became faster. The results implied that the Mg substitution is beneficial to develop tritium storage alloys with good kinetics.The structures and hydrogen storage performance of annealed La(1-x)MgxNi4.25Al0.75(x=0.0, 0.1, 0.2, 0.3) alloys were also investigated in this work. It is found that LaNi4 Al phase was the main phase in the alloys. For x=0.2 and 0.3, however, the secondary phases(La, Mg)Ni3 and Al Ni3 can be observed. The abundances of the secondary phases increased with increasing Mg content. There is one plateau in the PCT curves for the alloys with x=0.0 and 0.1. While two plateaus appeared in the curves for the alloys with x=0.2 and 0.3. As the increase of Mg content from 0.2 to 0.3, the plateau pressures of the alloys raised correspondingly. At the same time, their hydrogen storage capacities decrease from 0.97 wt.% to 0.79 wt.%. The alloy with x=0.1 has the fastest absorption kinetics among these alloys, and its plateau pressure and hydrogen capacity are almost the same as those of LaNi4.25Al0.75 alloy.ZrCo0.8M0.2(M=Co, Cu, Cr, Mn and Al) alloys were prepared via arc melting method under argon atmosphere. The major phases of the alloys were ZrCo structure. But the partial substitution of Co by Cr, Mn and Al lead to formation of secondary phases. The Zr2 Co and ZrCr2 phases were formed for the Cr substitution. The Zr2 Co and ZrMn2 phases were formed for the Mn substitution. The Zr3 Co and Zr6CoAl2 phases were formed for the Al substitution. The cell volume of the alloys decreased with the Cr and Mn substituting, and increased with the Cu and Al substituting, respectively. The hydrogen storage capacity of the alloys decreased with Cu, Cr, Mn and Al substitution. But desorption plateau pressure of the alloys was nearly unchanged. The activation performance of ZrCo alloy was effectively improved with the addition of Cr and Mn at room temperature. The degree of disproportionation reaction was increased for the Zr Co0.8M0.2(M=Co, Cu, Cr, Mn and Al) alloys. But the rate of disproportionation reaction was decreased for the alloys with the addition of Cr and Mn due to the driving force of disproportionation decreased. Comparing the lattice constant and kinetics of disproportionation, it could be inferred that the radius of hole sizes of less stable hydrogen occupation sites decreased with the Cr and Mn substitution, thereby reducing the proportion of hydrogen atom occupying these sites and the driving force of disproportionation. This resulted in the decrease of the rate of disproportionation. |
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