Flaky FeSiAl powders with high permeability towards broadband microwave absorption through tuning aspect ratio

Optimizing aspect ratio of flaky powder plays a crucial role in improving broadband microwave absorption performance. Herein, the aspect ratio of flaky FeSiAl powder has been successfully controlled through changing the ball-powder ratio. And with the increment of ball-powder ratio, the aspect ratio of flaky FeSiAl powder basically increases until the ball-powder ratio is higher than 20:1. It is also proved that annealing can effectively increase crystallinity, release internal stress, and promote crystal growth. Due to variable aspect ratio, flaky FeSiAl powders show different electromagnetic properties. In MHz range, the permeability increases with the aspect ratio of the flaky FeSiAl. In GHz range, higher aspect ratio would lead to higher permittivity, which should be ascribed to increased conductivity and enhanced polarization. Meanwhile, moderate aspect ratio results in strongest magnetic loss at lower frequency and low aspect ratio brings about strongest magnetic loss at higher frequency. Although attenuation capability of FeSiAl powders would be enhanced with large aspect ratio, their impedance matching performance would also gradually deteriorate. Consequently, only appropriate aspect ratio can give rise to promising microwave absorption performance. In this work, flake FeSiAl powder with a proper aspect ratio of ~ 3:1 exhibits a broad effective absorption bandwidth of 6.08 GHz at 2.15 mm. This work may provide novel reference for the synthesis and application of flaky metallic powders as broadband microwave absorbing material.