Effect of particle size on the preparation and microwave absorption properties of FeSiAl magnetically soft alloy hollow microspheres

FeSiAl magnetically soft alloy hollow microspheres (MSAHMs) were prepared by self-reactive quenching technology based on Fe + Si + Al + KNO3 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, Fe3Si0·7Al0.3 and Fe3Si0·5Al0.5 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.