Structure and microwave properties of Fe75Si25 alloys produced by high-energy wet ball milling in organic media

Abstract

Fe-Si alloys are known for excellent soft magnetic properties and are widely used as fillers of composite for microwave applications. A change in the size and the morphology of the powder particles has a significant influence on the microwave properties of composites filled with such powders. In this paper, Fe75Si25 powders were produced by wet ball milling. A solution of stearic acid in petroleum ether (a surfactant solution) and acetone were used as milling media. The influence of wet ball milling conditions on the morphology and the structure of the produced powders was studied by scanning electron microscopy, X-ray diffraction, Mossbauer spectroscopy and X-ray photoelectron spectroscopy. Wet ball milling of the alloy in an acetone leads to the formation of the particles of greater thickness and smaller size in comparison with the particles produced by wet ball milling in a surfactant solution. In both cases after milling the alloy is disordered. During the milling process Si concentration in the alloy decreases due to the formation of surface oxide layers enriched with silicon. The frequency dependence of microwave permittivity and permeability of composites filled with produced powders was studied. The depolarization factor, percolation threshold, and intrinsic permeability of produced powders particles were determined. The frequency dependence of intrinsic permeability of the particles was shown to depend strongly on the milling conditions. A change in the milling conditions makes it possible to produce Fe75Si25 powders with the required microwave properties.