Nanosized powders of iron silicides were prepared by the are plasma method. These silicide powders were characterized by X-ray diffraction and transmission electron microscopy. The lattice vibrations of nanosized epsilon-FeSi were investigated by Fourier-transformation infrared spectroscopy and compared with those of bulk FeSi. To determine the stability of different iron silicides, powder mixtures of epsilon-FeSi and alpha-FeSi2 were treated thermally in different atmospheres, and at high pressure as well. The different behaviors of alpha-FeSi2 could be understood by means of the thermodynamics and kinetics of structural transformation in nanosized alpha-FeSi2 grains. (C) 2000 Elsevier Science Ltd.