Monodisperse iron-based particles: precipitation in liquid polyols

Abstract

Fine equiaxial α-Fe particles were obtained by disproportionation of iron(II) hydroxide in liquid polyols with yields in the range 5–8%. The influence of the polyols as the reactive medium upon the solid phase formation during this reaction and its effect upon the Fe formation yield are discussed. Fine polymetallic powders Fe_xM_(100–x)(M = Ni, Co; 0 ⩽x⩽ 25) and Fe_x[Ni_yCo _{(1 – y)}]_{(100 –x)}(0 ⩽x⩽ 25; 0 ⩽y⩽ 1), were prepared from mixed hydroxides in liquid polyols, with metallic iron being generated in solution by disproportionation, and metallic nickel and/or cobalt by reduction of Ni^II and Co^II hydroxides by the polyols. Characterization (using X-ray diffraction, energy dispersive spectroscopy and electron microscopy) showed FeNi powders, made up of spherical particles with a mean diameter (d_m) in the sub-µm size range, a narrow size distribution (standard deviation σ < 10%d_m) and a fairly good homogeneity of composition; FeCo powders were polyphasic and made up of polydisperse agglomerates of Fe and Co particles while FeNi powders appeared as a single phase; FeCoNi powders appeared as monodisperse and polyphasic. The growth mechanism of the particles is discussed in relation to their characteristics: for FeNi monodisperse particles a growth mode by aggregation of nm-sized primary particles is proposed.