FeSiAl magnetically soft alloy hollow microspheres(MSAHMs) were prepared by self-reactive quenching technology based on Fe + Si + AI + KNO_3 reactive systems, in order to obtain absorbents with light weight, low frequency and high efficiency. Firstly, twice-balling adhesive precursor method was used to obtain FeSiAl magnetically soft alloy agglomerate powders. Then agglomerate powders with the mesh number of 150-240, 240-325 and 325-400 were sprayed through the flame field into the quenching water. At last, FeSiAl MSAHMs with coarse(average at 86.97 μm), medium(average at 52.16 μm) and fine particles(average at 31.80 μm) were got. Effect of particle size on the phases and microwave absorption properties in low frequency band was studied by XRD and vector network analyzer. The results show that,Fe_3 Si_(0.7)Al_(0.3) and Fe_3 Si_(0.5)Al_(0.5) appear in the phase components of FeSiAl MSAHMs,which is important to improve the microwave absorption properties in low frequency. In addition, the real part(ε′) and imaginary part(ε″) of complex permittivity, the real part(μ′) and imaginary part(μ″) of complex permeability of FeSiAl MSAHMs all present the trend of fine particles > medium particles > coarse particles. The microwave absorption properties in low frequency are improved with the increasing of particle size, and the absorption peak moves to lower frequency range. The properties of fine particles are the best. Their matching thickness of samples is at 5 mm, and the minimum reflectivity is-43 dB at this thickness. The absorption frequency band lower than-10 dB is 4.6-7.6 GHz with a bandwidth of 3 GHz.
Al+Ba O2 +Fe2O3 +sucrose and O2 as reaction system and feeding gas, respectively, are used to prepare hollow multiphase ceramic microspheres(HMCMs) absorbent based on self-reactive quenching technology. The morphologies, particle size distribution,hollow structure and phase compositions were characterized by scanning electron microscope(SEM), X-ray diffraction(XRD) and size analysis. The results show that the quenching products possess high sphere-forming rate, and most of them are hollow structures. Owing to the self-burst,the particle size is between 40 and 70 lm. The phase compositions contain Al2O3, Fe3O4, Fe2O3, Ba2Fe14O22,Ba O2 and Ba Fe4O7. The microwave absorbing tests show that the lowest reflectivity of HMCMs is-19 d B. The frequency bands less than-10 d B are from 13.0 to15.8 GHz. The reasons for HMCMs possessing good microwave absorbing properties may be their magnetic and electrical properties as well as special hollow structure.
