GHz microwave absorption of a fine α-Fe structure produced by the disproportionation of Sm2Fe17 in hydrogen

In this study, the possibility of using the disproportionation reaction of the Sm2Fe17 compound for the production of powders with a fine alpha-Fe structure was investigated, for use as electromagnetic wave absorbers that can operate in the GHz frequency range. A fine alpha-Fe/SmH2 or alpha-Fe/SmO structure with a sub-micrometer size is formed from the Sm2Fe17 compound after disproportionation in hydrogen or air, respectively. In this way, magnetic powders with a fine structure of alpha-Fe were obtained. The powders disproportionated in hydrogen, were heated in air in order to oxidize the Sm hydride, to give a alpha-Fe/SmO two-phase microstructure, and thereby increase the resistivity of the powders, Toroidally shaped epoxy-resin composites were made from this powder, and the microwave absorption properties of these samples were measured. An undisproportionated sample did not show any electromagnetic wave absorption in this frequency range. However, the disproportionated samples (heated in hydrogen at 873 K for I h, milled for 30 min and oxidized at 473 K for 2 h in air) exhibited electromagnetic wave absorption (RL<-20 dB) in the frequency (f(m)) range 0.73-1.30 GHz for absorber thicknesses (d(m) ranging from 13.1 to 7.9 mm, respectively. The disproportionated samples in air (heated at 473 K for 2 h and milled for 30 min) also showed good electromagnetic wave absorption properties (f(m) = 1.21-2.50 GHz: and d(m) = 8.0-4.2 mm). It is concluded that the disproportionation reaction, in either hydrogen or in air, is a useful method for the production of powders with a fine a-Fe structure, which can be used for microwave absorbers that operate in the several GHz range. (C) 2002 Elsevier Science B.V. All rights reserved.