Broadband microwave absorption and mechanical properties of CB-CIP@SiO₂-GF/PA6 composites

With the aim of broadening the absorption band of structural microwave absorbing composites, a magnetic loss absorber carbonyl iron powder (CIP) and the resistive loss absorber carbon black (CB) were simultaneously introduced into glass fiber reinforced polyamide 6 composites, and CB-CIP@SiO₂-GF/PA6 composites were prepared by the hot press molding process. Focusing on the effect of CIP surface coated SiO₂ film and its incorporation on the microwave absorption and mechanical properties of composites. The results show that SiO₂ coating not only prevents the oxidation of CIP, but also improves the impedance matching of the composites, so that CIP and CB synergistically enhance the microwave absorbing properties of the composites. Under the premise of guaranteeing good microwave absorbing properties, the loading of CIP is reduced from 70 wt.% to about 30 wt.%, which greatly lightens the mass of the composites. The effective absorption bandwidth of the composites with 1 wt.% CB and 30 wt.% CIP@SiO₂ exceeds 5.6 GHz at a thickness of 1.91-1.95 mm and covers the entire Ku-band. On the one hand, this method broadens the effective absorption bandwidth of the composites and realizes broadband absorption. On the other hand, the particle reinforcement of CIP@SiO₂ has a co-enhancing effect with GF. When the content of CIP@SiO₂ was 40 wt.%, the mechanical properties of the composites were optimal, with a flexural strength of 212.8±9.8 MPa, a shearing strength of 21.0±1.4 MPa, and a pendulum impact strength of 64.4±6.2 kJ/m².