Effect of NaNO sub(3) foaming agent on barium ferrite hollow microspheres prepared by self-reactive quenching technology

Al + Fe sub(2)O sub(3) + BaO sub(2) and NaNO sub(3) as the reactive system and the foaming agent, respectively, are used to prepare barium ferrite hollow microspheres (BFHMs) by self-reactive quenching technology based on flame spraying technology, self-propagating high-temperature synthesis (SHS) technology and quick chilling technology. Effects of NaNO sub(3) on the particle size, morphology, phase structure and microwave absorption properties of BFHMs are investigated through SEM, XRD, particle size analyzer, high-speed camera and vector network analyzer. The results show that, after adding 10wt.% NaNO sub(3), the average particle size of BFHMs decreases initially from 28 mu m to 6 mu m, as well as the particle distribution gets narrower. Micro-nano lamellar crystals appear on the surface of BFHMs, with the dimension ranging from 500 nm to 2 mu m. BaFe sub(2)O sub(4) and Fe sub(3)O sub(4), which have spinel structures, can be seen in XRD, and they are beneficial for microwave absorption properties. The real part ([varepsilon]'), imaginary part ([varepsilon]") of permittivity, and the imaginary part of permeability ( mu ") increases in 0.5-18 GHz. The real part ( mu ') of permeability increases in 0.5-10.3 GHz, while decreases in 10.3-18 GHz. The microwave absorption properties are improved greatly, and the minimum reflectivity decreases from -3.1 dB to -9.8 dB. The reasons for improvement of microwave absorption properties after adding NaNO sub(3) foaming agent may be the decreasing of the particle size of BFHMs, the appearance offerrites (BaFe sub(2)O sub(4) and Fe sub(3)O sub(4)) with spinel structure and special micro-nano tabular crystals. Magnetoplumbite-type barium ferrites (BaFe sub(12)O sub(19)) hollow microspheres are obtained after heat-treatment and the microwave absorption properties are further improved.