The influence of a surfactant on the characteristics of the iron powders obtained by mechanical milling in organic media

Abstract

X-ray diffraction, Mössbauer spectroscopy, Auger spectroscopy and magnetic measurements have been used to investigate the effect of surfactants (oleic acid) on dispersion, structure, phase composition and magnetic behaviour of powders, obtained by milling of iron in a planetary ball mill in liquid hydrocarbon environment (heptane). The presence of a surfactant brings forward the dispersion increase in the powders, the change of the particle shapes and their magnetic characteristics. Namely, after 99 h treatment the 20-fold increase of coercitivity and 2-fold decrease of specific saturation magnetization was observed. The resulting powders have nanocrystalline structure (grain size ≈4 nm) and represent supersaturated solid solution of O and C in α-Fe with Fe 3C as impurities. The concentration of C and O, with heptane (C) and oleic acid (C,O) as their source, increases with milling time. The change of magnetic characteristics has been shown to depend on the content of C and O in the powders.