EFFECT OF MISH METAL TYPE ON THE MICROSTRUCTURE AND ABSORPTION/DESORPTION CHARACTERISTICS OF MMNI5 HYDROGEN STORAGE ALLOY

In this article, the effects of Pr and Nd were investigated on the microstructure and absorption/desorption characteristics of MmNi5 hydrogen storage alloy. The alloys were prepared in Vacuum induction furnace and the microstructures and phases were analyzed using scanning electron microscopy (SEM) equipped with energy dispersive X-ray analysis (EDS) and X-ray diffraction (XRD). Hydrogen absorption/desorption characteristics was performed on Sievert apparatus. The results showed that the microstructure of the alloys consist of matrix, second phase as a result of Al segregation, porosities and cracks. The amount of second phases and Al in this phase in Mm(Pr,Nd)Ni4.7Al0.3  is less than MmNi4.7Al0.3. Al in Mm(Pr,Nd)Ni4.7Al0.3 were more homogenized. Pressure-Composition Isotherms of hydrogen absorption/desorption at 25˚C showed that for MmNi4.7Al0.3 and  Mm(Nd,Pr)Ni4.7Al0.3, absorption pressures were 14.52 and 9.90 bar,  desorption pressures were 5.53 and 5.49 bar, hydrogen storage capacities were 1.37 and 1.33 wt. % and hysteresis were 0.73 and 0.58, respectively. These results are useful in industrial applications, because of inconsiderable decrease in hydrogen storage capacity and the other positive variation in absorption/desorption characteristics, especially the hysteresis and absorption pressure.