Some Influencing Factors And Related Catalytic Mechanism Of TiAl₃ On Hydrogenation/Dehydrogenation Of NaAlH₄

is one of the hydrogen storage materials due to its high-capacity and low dehydriding temperature, but its hydriding and dehydriding kinetics are poor. Nowadays researchers mainly focus on seeking for effective catalysts and studying the catalytic mechanism for NaAlH4 hydrogen storage system.In the thesis, powder sintering method was adopted to produce TiAl3/Al interfaces, and TiAl3-NaAlH4 were in-situ synthesized by vibration ball-milling under high H2 pressure; The XRD, TG-DSC, hydriding and dehydriding kinetic tests were adopted to study the influencing factors and related catalytic mechanism of TiAl3/Al interface on hydrogenation/dehydrogenation of NaAlH4.Usually, catalyst was needed to contact with the reactants for catalysis. It is not easy to form the effective contact for TiAl3 with NaH, but for TiAl3 with Al, it is easy to form. In the chapter 4, powder sintering was used on the mixture of TiAl3 with Al, whether the catalytic effect of TiAl3 improved was studied after the TiAl3/Al interfaces produced. It was shown in the XRD pattern that only peaks of TiAl3 and Al existed, the interfaces of TiAl3/Al could produced after sintered. Then the as-sintered particles of TiAl3-Al were vibration ball-milled 40 h under the 8 MPa H2 atmospheres with NaH. The hydrogen capacity of the sample after ball-milled reached to 3.96 wt.%; the hydriding saturated time of the sample after dehydrogenated were 1.2 h, it was indicated that the system with decent catalytic effect. In addition, as-sintered Ti-Al in catalytic effect situation was slightly lower than as-sintered TiAl3-Al. While the comparative samples which did not sintering corresponding exhibited a hydrogen capacity of 1.69 wt.%and 1.98 wt.%after ball-milled, the hydriding saturated time were 14 h for the non-sintering two samples after dehydrogenated. It was shown from the experimental results that the hydrogen storage capacity and hydriding kinetic performance were both increased a lot after sintered, which was closely related to the interface of TiAl3/Al formed during sintering.High temperature and small particle size are favorable factors for the formation of the TiAl3/Al interfaces. In the chapter 5, it was shown in the hydriding kinetic results that the hydriding kinetic performance improved with the increment of sintering temperature; with the increment of the sintering temperature and the decrease of the TiAl3 particle size, the hydriding kinetic performance showed a trend of increase after dehydrogenated. It was indicated that the better hydriding/dehydriding performance will achieved when more TiAl3/Al interfaces produced.In the chapter 6, thermal analysis kinetic research method was used to calculate the kinetic parameter of the two samples were preparated by powder sintering of Ti with Al and TiAI3 with Al in the first part. It was revealed in the result that the two decomposition steps of the two samples conform to the nucleation and growth mechanism. Grain size of the Al after the first and the second decomposition steps were calculated by the Scherrer equation. It was shown in the result that the grain size of Al after the second decomposition step was larger. It was concluded that the Al could participated in nucleation and growth process in NaAlH4 dehydrogenation. It was indicated that Al nucleated around the TiAl3, and the Al grain size was limited in the decomposition of NaAlH4, this process could improved the dehydriding kinetics of NaAlH4. While the reaction of hydrogenation took place in the interface of TiAl3/Al, the more interfaces, the faster NaAlH4. produce.