• MAHDI ABBASI SEYED

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    • Microstructure and thermodynamic assessment of MmNi5-xAlx hydrogen storage alloys

      SEIFOLLAHI MASUMEH JOUDAKI MOHAMMAD MAHDI ABBASI SEYED MAHDI GHAZI MIR SAEED SEYED

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      The microstructures and thermodynamic properties of MmNi5-xAlx hydrogen storage alloys are studied in this article. The structure was assessed with XRD and SEM. Pressure-composition isotherms for hydrogen absorption/desorption at 0, 25 and 50 ̊C were used for assessment of thermodynamic properties. XRDresults show that the samples consist of single-phase CeNi5–type. The alloys exhibit second phases, porosities, and cracks. Al microsegregation is the main reason for the second phase formation. With increasing Al, the microsegregation and the amount of second phases are increased. The hydrogen storage capacities of MmNi5- xAlx (x = 0.2, 0.3, 0.4 at %) alloys are 1.40, 1.37 and 1.34 wt%, respectively. The equilibrium pressures and hysteresis (1.14, 0.96 and 0.72 for 0.2, 0.3 and 0.4 Al, respectively) for all three compositions decrease withincreasing Al, that proves the formation of more stable hydrides. Furthermore, the enthalpy of hydride formation decrease to -20.770, -23.565, -26.306 kJ mol-1 H2 for the MmNi5-xAlx (x = 0.2, 0.3, 0.4 at %) alloys, respectively. This shows the improvement of thermodynamic stability and properties.

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