Formation of β-FeSi2 and the remanent α-Fe

Measurement of x-ray diffraction patterns, Mossbauer spectra, Raman scattering spectra and HRTEM/EDAX for β-FeSi2 obtained by milling Fe30Si70 and HCl treatment shows that the Fe is not exhausted in the final product. There are two reactions during the ball milling process: one is the surface reaction to produce β-FeSi2 between Fe and Si by driving force; some α-Fe is surrounded by β-FeSi2. Another process is that Si diffuses through the β-FeSi2 layer and reacts with Fe inside. However, this cannot exhaust all the Fe inside the grain, so the α-Fe still exists although there is little. The two processes coexist during the ball milling procedure, but the first process plays the main role for the first 50 h, then the second process mainly influences the proportion of α-Fe.