AN ELECTROCHEMICAL INVESTIGATION OF NANOCRYSTALLINE Mg₂Ni_0.75Nb_0.25 COMPOUND SYNTHESIZED BY MECHANICAL ALLOYING

The effects of mechanical alloying on the microstructure of binary and ternary powder mixtures with stoichiometric compositions of Mg₂Ni and Mg₂Ni_0.75Nb_0.25 were studied, respectively. Also, the electrode properties of the milled products were investigated in 6M KOH solution. X-ray diffraction and scanning electron microscopy of the milled products showed the formation of Mg₂Ni-based nanocrystallites after 15 and 10h of milling using the initial binary and ternary mixtures, respectively. It was found that partial substitution of Nb for Ni has beneficial effect on the formation kinetic of nanocrystalline Mg₂Ni. Longer milling times resulted in the formation of an amorphous phase. A relatively high discharge capacity of 350mAhg^-1 was measured for the electrode made up of the ternary milled product after 20h. Also, the ternary milled product showed longer discharge life. This ternary electrode showed a microstructure consisting of Mg₂Ni nanocrystallites and an amorphous phase. Nb substitution for Ni was found to be beneficial to electrode properties of the milled products.