SYNTHESIS OF MMNI4.5AL0.5 BY MECHANICAL ALLOYING

The synthesis of aluminium substituted mischmetal pentanickelides (MmNi4.5Al0.5) using ball milling is reported. A stoichiometric mixture of mischmetal, nickel and aluminium when subjected to ball milling for 100 h in argon atmosphere led to the formation of MmNi4.5Al0.5. The synthesized powder was characterized by X-ray diffraction and transmission electron microscopy. The low temperature annealing of the ball milled powder (600-degrees-C, 30 min) has been found to improve the crystallinity. The ball milling followed by low temperature annealing yielded an MmNi4.5Al0.5 phase nearly identical to the one prepared through high temperature melting of the ingredients. Both XRD and TEM characterizations have confirmed the formation of the alloy MmNi4.5Al0.5. Extensive electron microscopic investigation revealed the presence of the modulated phase in local regions with modified periodicities (a = 4a(o) and c = 2c(o)).