Abstract
It was reported in our previous papers that the disproportionation reaction of the Sm2Fe17 compound in hydrogen can be used to prepare fine, soft-magnetic powders for use in electromagnetic wave absorbers. In this study, the microstructure and electromagnetic wave absorption properties in the GHz frequency range of Sm2Fe17 powders, disproportionated in air or nitrogen atmospheres, were investigated. A fine α-Fe structure, of sub-micron order size, is formed from the Sm2Fe17 compound after disproportionation in either air or nitrogen. In the case of disproportionation in air, the powder treated at 423–573 K was in a α-Fe/SmO two-phase state. While in the case of disproportionation in nitrogen, the powder treated at 923 K showed α-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 were made from these powders, and their electromagnetic wave absorption properties 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 absorber thickness was between 7.2 to 4.2 mm. Therefore, compared with a carbonyl-iron/resin composite (which had the same Fe content), the absorber was 30% thinner.
