Effect of M. G. on the Preparation of Sintered β-FeSi₂

Abstract

Effect of mechanical grinding (M.G.) process on preparing β-FeSi₂ for thermoelectric generator by useing hot presssing (H.P.) was investigated by X-ray diffraction, EPMA and SEM.
Mixture of Fe and SI powders was arc-melted in an argon atmosphere to form a button composed of α-Fe₂Si₅, and ε-FeSi phases. The button was grinded in a conventional ball-mill for 20-650hr. X-ray diffraction analysis showed that the peaks of ε and α-phases disappeared after 250 and 650hr, respectively. The ball-milled powders were hot pressed at 1110°C for 30min under 25MPa and heat treated at 840°C for 10hr and 20hr. The heat treated samples were composed of mostly β-phase with small amount of ε-phase and their relative densities were more than 99%. The amount and size of the ε-phase decreased with increasing ball milling time. The result showed that mechanical grinding strongly accelerated the formation of β-phase. Almost the same results were obtained oil hot pressing at 900°C for 30min without heat treatment.