Description:
Good thermal stability and low thermal expansion is a critical challenge for magnetic microwave absorbers in the engineering applications. Herein, we develop a low-cost and large-scale electrical discharge method to design high-thermostability FeCoNi Kovar alloy microwave absorber to address the low-frequency absorption issue. The spherical fine FCN powders are achieved from thermal ablation of bulk alloys by this technique, which possess a dual-peak size distribution and give the strongest RL value at -40 dB at frequency of 10.8 GHz with a qualified frequency bandwidth of 5.7 GHz from 8.2 to 13.9 GHz. To exceed the Snoek’s limit, ball-milling method is applied to flatten FCN powders. With increasing the ball-milling time from 12 h to 36 h, the microwave attenuation shifts to lower frequency band. FCN-36 powders achieve a maximum RL value of -50.1 dB at 3 GHz. Good conductive loss among the overlapped flaked powders with a papillated surface, well dielectric loss caused by interface and dipolar polarization between oxide coating layer and metal bases, smaller grain size and the nature resonance contributes to enhance the electromagnetic wave energy conversion. The research demonstrates a new inspiration toward the preparation of metallic microwave absorbers in large-scale and provides novel alloy powders for microwave absorption in low-frequency range