Fabrication And Hydrogen Storage Performance Of Ti Type Composite Alloys

As a typical representative of AB hydrogen storage alloy,TiFe alloy has a high theoretical hydrogen storage capacity and can reversibly absorb and release hydrogen at room temperature.The source of raw materials for TiFe alloy is also extremely rich,and the preparation cost is low.However,the activation conditions of the TiFe alloy are very severe,and the hysteresis of the alloy is also large,and these problems seriously hinder the further commercial application of the TiFe alloy.In this dissertation,TiFe-based hydrogen storage alloys with excellent activation properties were prepared by vacuum arc melting and induction melting,through elements substitution and the modification of composite materials.The composition,phase structure and surface morphology of hydrogen storage alloys were characterized,and the hydrogen storage and kinetic properties of materials were tested and analyzed.And the hydrogen storage and compression properties of Ti-based hydrogen storage alloys for static hydrogen compression were also studied.The research shows that the TiFe alloy was partially substituted with B-side Mn element.The main phase of the prepared Ti-Fe-Mn ternary alloy was TiFe phase,but with the addition of Mn,the cell parameters increased.The characteristic peak of the TiMn₂ phase appeared in the XRD pattern of TiFe_0.7Mn_0.3 and TiFe_0.6Mn_0.4.The TiFe_0.6Mn_0.4 alloy showed the best activation performance,and the hydrogen storage reached 1.1wt.%in a short incubation period at 393K during the first activation.The maximum hydrogen storage capacity of the alloy increased first and then decreased with the addition of Mn.The hydrogen storage capacity of TiFe_0.8Mn_0.2 alloy was the largest,and it was 1.71wt.%at 303K temperature.The addition of Mn also led to increase in the slope of the hydrogen absorption and desorption platform of the alloy,and the pressure of the hydrogen absorption and desorption platform of the alloy gradually decreased.On the basis of the Ti-Fe-Mn ternary alloy,the activation properties of the alloy were further optimized by the method of the composite material.A TiFe_0.8Mn_0.2+yMmNi₅ complex phase alloy with a molar ratio of 1:y?y=0.005,0.01,0.015,0.02?was prepared.When the molar ratio was greater than or equal to 1:0.015,the alloy was fully activated at 303 K and the hydrogen storage capacity was as high as 1.2 wt.%.When the molar ratio reached 1:0.02,the characteristic diffraction peak of LaNi₅ appeared in the XRD pattern of the alloy.The activation properties of the composite phase alloy were further optimized.However,the addition of MmNi₅ alloy would reduce the maximum hydrogen storage capacity of the alloy.For example,the alloy with a molar ratio of 1:0.02 showed the lowest hydrogen storage capacity of only 1.25wt.%?303 K?.According to the analysis,the activation model of the composite alloy is proposed:Firstly,the hydrogen was physically adsorbed on the surface of the alloy,and accumulated La on the surface preferentially activated and formed a La-H compound,then H diffused and transferred into the La-Ti transition region,finally entered the inside of the alloy to form a hydride.The activation process of the alloy had completed.In this dissertation,Ti-based high and low pressure hydrogen storage alloys for two-stage static hydrogen compressors were also prepared,and the preparation conditions were explored.Through the hydrogen storage performance test and theoretical calculation,the compression ratio of the low-pressure alloy was 6.92,and the compression ratio of the high-pressure alloy was 5.94,the hydrogen absorption pressure at 298K was 2.6 MPa,and the desorption pressure can reach 66.5 MPa when the temperature is raised to 373K through the theoretical calculation.