Phase Structures And Hydrogen Storage Properties Of Ti-Zr-Cr-Mn Based Laves Phase Multiple Alloys

In this thesis, the research and development of Ti-Mn based hydrogen storage alloys with Laves phase structure were exhaustively reviewed. Ti-Zr-Mn-Cr based alloys with good hydrogen storage properties were chosen as the objects of this study for improving the overall hydrogen storage properties by multi-component alloying and composite ball-milling. By means of XRD, SEM, EDS analysis and hydriding/dehydriding characteristic measurements, the microstructures and hydrogen storage properties of Ti-Zr-Mn-Cr quaternary alloys with variational Zr and Cr content, Ti-Zr-Mn-Cr-M based quinary alloys (M=V, Fe, Ni, Cu) and Mo-containing Ti-Zr-Mn-Mo-Cr-V based senary alloys with variational Mn content have been investigated respectively, and the catalysis of added Ti-Mn based alloy into Ti-V-Fe alloy by ball-milling has been investigated.The study on the phase structures and hydrogen storage properties of Ti_1.0Zr_0.1Mn_2-xCr_x(x=0.8, 0.9, 1.0, 1.1, 1.2) and Ti_1.1-xZr_xMnCr (x=0.0, 0.05, 0.1, 0.15, 0.2) alloys shows that all of these alloys have a main phase of C14 type Laves phase, and the unit cell volume increases with the increase of Zr or Cr content. It is found that the activation behavior of the alloy is improved as Zr or Cr content increases, for example, Ti_1.1CrMn alloy could not be activated at room temperature and under 8 MPa hydrogen pressure, Ti_1.05Zr_0.05MnCr and Ti_1.0Zr_0.01Mn_1.2Cr_0.8 can be activated after 4 cycles (at room temperature and under 7 MPa hydrogen pressure) and after 5 cycles (at room temperature and under 6 MPa hydrogen pressure) respectively, the rest alloys can be activated after 3 cycles at room temperature and under 6 MPa initial hydrogen pressure without hydrogenation incubation period. After activated, all the alloys have very fast kinetics that can absorb saturated hydrogen within 3-5 minutes. With the increase of Zr content, the maximum hydrogen absorption capacity at room temperature increases, the effective hydrogen desorption capacity increases first and then decreases. With the increase of Cr content, the maximum hydrogen absorption capacity and effective hydrogen desorption capacity both increase first and then decrease. Among these alloys studied, the Ti_0.9Zr_0.2MnCr alloy has a good overall property, such as the activation number of 3 cycles, the maximum hydrogen absorption capacity of 2.02 wt.% and the effective hydrogen desorption capacity of 1.63 wt.% at room temperature.The study on the phase structures and hydrogen storage properties of Ti_1.0Zr_0.1MnCr_0.8M_0.2(M=V, Fe, Ni, Cu) alloys shows that after partial substitution of Cr with V, Fe, Ni or Cu, the phase structure of the alloy almost is not changed, and the activation performance is improved, all the alloys can absorb hydrogen rapidly and be fully activated in the first cycling at room temperature and under 6 MPa hydrogen pressure, especially the modifying effect of V is very obvious. The partial substitution of Cr with V, Ni or Cu results in the increase of the unit cell volume and hydrogen absorption capacity. The partial substitution of Cr with Fe results in the decrease of the unit cell volume and hydrogen absorption capacity, however, the effective hydrogen desorption capacity reaches the largest amount of 1.61 wt.%.The study on the phase structures and hydrogen storage properties of Mo-containing Ti_0.95Zr_0.15Mn_1.4+xMo_0.1Cr_0.2V_0.2(x=0.0, 0.1, 0.2, 0.3) alloys shows that all of these alloys consist of C14 type Laves phase, and the unit cell volume decreases with the increase of Mn content. All alloys can be activated after 2 cycles at room temperature and under 4 MPa initial hydrogen pressure, only through a hydrogenation incubation period of beyond 30 min at the first cycle. With the increase of Mn content, the hydrogen absorption capacity deceases, but the effective hydrogen desorption capacity at room temperature increases, thereinto, the Ti_0.95Zr_0.15Mn_1.4Mo_0.1Cr_0.2V_0.2 alloy has the largest hydrogen absorption capacity of 2.01 wt.%, and the Ti_0.95Zr_0.15Mn_1.7Mo_0.1Cr_0.2V_0.2 alloy has the largest effective hydrogen desorption capacity of 1.76 wt.% .The influence and catalysis of composite ball-milling with 10 wt.% Ti_0.9Zr_0.1Mn_1.5 on the hydrogen storage properties of Ti_9.6V_86.4Fe₄ alloy have been investigated. The results show that the as-cast Ti_9.6V_86.4Fe₄ alloy has a single vanadium-based solid solution phase with BCC structure, and the ball-milled composite has a C14 type Laves secondary phase besides the BCC solid solution main phase. Comparing with the as-cast Ti_9.6V_86.4Fe₄ alloy, the unit cell volume of the main phase of the ball-milled composite increases slightly. The Ti_0.95Zr_0.15Mn_1.5 has a good catalysis on the activation behavior of Ti_9.6V_86.4Fe₄. The ball-milled composite can be fully activated only in the first cycle. Comparing with the as-cast Ti_9.6V_86.4Fe₄ alloy, the maximum hydrogen absorption capacity of the ball-milled composite at room temperature decreases from 3.86 wt.% to 3.61 wt.%, however, the effective hydrogen desorption capacity increases from 2.01 wt.% to 2.11 wt.%, and the plateau characteristic of P-C-T curve is also improved.