The cyclic degradation of TiCrV hydrogen storage alloy has been studied by using SEM and TEM. Microstructural analysis indicated that the accumulation of lattice defects such as dislocations and strain field occurred due to volume expansion and shrinkage during cycles, led to a loss of the effective storage capacity. Annealing with minute particles in order to suppress the development of lattice defects during cycles resulted in increase in plateau width during hydrogenation but nothing improved during de hydrogenation. This is probably due to beta hydrides formed during hydrogenation, which is stable with lattice defects and strain field. Fine particles less than several hundred nano meter in size could have a good degradation resistance due to less accumulation of lattice defects and during cycles.
The purpose of this study is to increase the rechargeable hydrogen storage capacity of Titanium Chromium Vanadium (Ti Cr V) body centered cubic (BCC) solid solution alloy by making a uniform alloy with high crystallinity and homogeneity on the nano scale. The samples were prepared by a melt quenching method, and the effects of this method on the BCC alloy were investigated using X ray diffraction, optical and electron microscopies, and a pressure composition temperature (P C T) analyzer. It was found that the quenched alloy had highly crystalline, sub micron scale crystals and a high dislocation density compared with the arc melted alloy. As a result, the plateau in the P C T characteristics became a steep slope with large hysterisis. The quenched alloy was heat treated to improve this plateau. This caused an increase in the grain size and a decrease in the dislocation density of the alloy; however, its high crystallinity was retained. The heat treated alloys had a high maximum and rechargeable hydrogen storage capacity and a flat plateau in their P C T characteristics. As a result, the rechargeable hydrogen storage capacity reached 2.56 mass in the pressure region of 0.1 4.5 MPa at 293 K. Keywords: melt quenching, hydrogen storage alloy, body centered cubic alloy, titanium chromium vanadium alloy, crystallinity, dislocation density, pressure composition isotherms
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