Electromagnetic microwave absorption properties of a fine structure formedfrom the Sm2Fe17 compound after disproportionation in air or nitrogen

It was reported in our previous papers that the disproportionation reaction of the Sm2Fe17 compound in hydrogen can be used to prepare fine, soft-magn etic powders for use in electromagnetic wave absorbers. In this study, the microstructure and electromagnetic wave absorption properties in the GHz fr equency range of Sm2Fe17 powders, disproportionated in air or nitrogen atmo spheres, were investigated. A fine alpha -Fe structure, of sub-micron order size, is formed from the Sm2Fe17 compound after disproportionation in eith er air or nitrogen. In the case of disproportionation in air, the powder tr eated at 423-573 K was in a alpha -Fe/SmO two-phase state. While in the cas e of disproportionation in nitrogen, the powder treated at 923 K showed alp ha -Fe/SmN two-phase state, this powder then had to be heated at 423-523 K in air in order to oxidize the SmN phase. Epoxy-resin composite samples wer e made from these powders, and their electromagnetic wave absorption proper ties were measured. It was found that the sample disproportionated at 923 K for 2 hours in a nitrogen gas flow, milled for 30 minutes and oxidized at 523 K for 2 hours in air, exhibited the best absorption properties. The R.L . value was under -20 dB in the frequency range 1.2 to 2.3 GHz, when the ab sorber thickness was between 7.2 to 4.2 mm. Therefore, compared with a carb onyl-iron/resin composite (which had the same Fe content), the absorber was 30% thinner.