Grinding speed dependence of microstructure, conductivity, and microwave electromagnetic and absorbing characteristics o
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ake-like Fe particles with controllable size and structures were achieved by modulating only the grinding speed; evidence provided by x-ray diffraction, scanning electron microscopy, resistivity measurement system, and vector network analyzer disclosed the conductivity; and microwave electromagnetic (EM) and absorbing characteristics of the resultant products strongly depended on their morphology and structure. As grinding speed (V) increases from 0 to 250 revolutions per minute (rpm), the crystalline size decreases; meanwhile, both internal strain and diameter/thickness ratio increase and the conductivity reaches the maximal value at V 5 140 rpm because of the improvement of the surface conductivity. Thin flake-like Fe particles facilely obtained at high grinding speed present higher values of the permittivity and permeability than spherical particles, which are ascribed to the multiple polarizations and the natural resonance. Thus, the aforementioned products with high permeability and low cost may be promising candidates for EM compatibility materials. I. INTRODUCTION
Recently, there are considerable interests in exploiting high permeability of soft ferromagnetic metal/alloys to fabricate magnetic objects for the growing demands of electromagnetic (EM) compatibility devices application, such as EM wave absorbers or shielding materials. For this purpose, numerous efforts have been focused on the investigation of EM characteristics and absorbing mechanism of flaked ferromagnetic metal/alloy particles owing to their advantages of high saturation magnetization, low eddy current loss, and large permeability value.1–6 So far, some magnetic metal/alloy flakes, such as Fe,1 FeCo/C,2 Fe3Co2,3,4 FeCoNi,5 FeCuNbSiB,6 Fe–Cr–Si–Al,7,8 Fe–Co–Zr,8 FeSiB,9 FeNi,10 etc., have been successfully fabricated. The theory discloses that shape anisotropy originating from flake-like structures may enhance the natural ferromagnetic resonant frequencies and exceed the Snoek’s limit. Interestingly, the modulation of intrinsic properties for flake-like structures can be achieved by tailoring its size, microstructure, morphology, and substitution of constituent elements. Among the above reported literatures, microstructural and morphological controls have been proved to be as effective as size and composition control in fine-tuning the properties and functions of flaked metal particles. Despite its fundamental and technological importance of the flaked particles, very limited attention has been a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.18 682
J. Mater. Res., Vol. 26, No. 5, Mar 14, 2011
http://journals.cambridge.org
Downloaded: 03 Sep 2014
paid for systematical investigation of the relationship between the microstructure and properties (e.g., conductivity, dielectric, dynamic magnetic, and microwave absorption characteristics) of flaked metal particles.1–14 In contrast to other preparation methods, mechanical milling developed by Benjamin15 is an advanced fabrication process to prepare ferromagneti
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