| 其他摘要 | Energy crisis and environmental pollution are urging many countries to develop new energies. Hydrogen energy and nuclear energy have many attractive advantages, such as high energy density, rich reserves and almost no pollution. They are new energies of the 21st century and will be applied in various living aspects of human beings.
As one of the three hydrogen isotopes, tritium has important strategic value. It is the fuel of nuclear reactor and one of important materials needed in manufacturing advanced nuclear weapons. Transport and storage for tritium is one of the key technologies in its application. Thus, the development of effective tritium storage material has practical significance.
On the basis of current domestic and oversea research status of tritium storage materials, LaNi5-xAlx(x=0～1.2) alloys were chosen to study in the present work. By the means of X-Ray diffraction (XRD), scanning electron microscope (SEM), laser particle size analyzer, hydriding-dehydriding test and micro-hardness test, material characteristics, such as the crystal structure, hydriding-dehydriding behavior, the relevant thermodynamics and kinetics characteristics, etc., were systematically studied. The hydriding-dehydriding test apparatus were designed and established.
It is found that the major phase existed in LaNi5-xAlx(x=0～1.2) is CaCu5-type structure. However, in LaNi3.8Al1.2, a tiny AlNi3 phase was observed. In the system, the increase of Al content mainly leads to decrease of hydrogen capacity and hydrogen pressure, but improves the kinetics. Via the home-made MATLAB program, it was found that Al element can increase the lattice volume at different expansion rates in a and c axis directions.
From systematic investigation of LaNi5-xAlx(x=0～1.2) cyclic properties, it can be concluded that the alloy’s pulverization resistance is determined by its character of plasticity, and is partially influenced by its hydrogen capacity. The lower the hardness and the hydrogen capacity of the alloy are, the better the property of pulverization resistance is. Besides, in the alloys, different tendencies of absorption kinetics were observed after long-term cycling. The kinetics of LaNi4.75Al0.25 and LaNi4.25Al0.75 alloys were degraded after cycling, while those of LaNi5 and LaNi3.8Al1.2 alloys were improved. The reason is that pulverization has opposite effects on kinetics. On one hand, pulverization produces more active interfaces and shorter hydrogen diffusion distances, which is beneficial to the kinetics. On the other hand, pulverization leads to worsen the transport of hydrogen gas and thermal conductivity, which finally results in the degradation of kinetics. When the particle size is comparatively large, the improvement of kinetics from pulverization becomes the dominant; while the particle size is comparatively small, the degradation of kinetics from pulverization becomes the key factor. For LaNi5-xAlx(x=0～1.2) alloys, the volume mean diameter (VMD) of the particle size distribution has a critical value, about 20 m. The discrepancy of absorption kinetics tendency between annealed induction-melted (AIM) and un-annealed melt-spun (UMS) LaNi4.25Al0.75 alloys after 1000 cycles also supports the viewpoint. Al element increases capacity stability of the alloys after long-term cycling.
From the study of hydrogen storage properties of AIM- and UMS- LaNi4.25Al0.75 alloys, it is found that these two alloys have good cyclic properties. But some discrepancies exist: the capacity degradation rate of the UMS alloy is faster than that of the AIM alloy; the pulverization resistance and hysteresis of the UMS alloy are better than those of the AIM alloy, while the capacity of the AIM alloy is a little bit higher, and the activation of the AIM alloy is easier.
The LaNi4.25Al0.75/SiO2 composites were successfully prepared by sol-gel method and fumed silica method. The composites keep good thermodynamic properties of the AIM-LaNi4.25Al0.75 alloy, while improving the kinetics, pulverization and activation properties.
A primary design scheme of 35MPa hydrogen feeding apparatus was provided in detail. This apparatus uses the metal hydrides as the working medium and can increase the pressure and purity of hydrogen gas from 1~2MPa and <99% to 35MPa and >99.999%, with the working temperature below 453K. The apparatus was designed as a structure of ‘two stages and three phases’, which facilitates the stable output of hydrogen gas with velocity of 100 l/min. |
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