Abstract: Lightweight and high-efficiency microwave shielding materials based on high absorption loss are the hotspot of current research. Herein, the silver-cobalt bimetallic hollow microspheres (Ag-Co-HM) with low reflection loss and broadband absorption efficiency were fabricated and then used to construct bimetallic hollow structures in polydimethylsiloxane/carbon nanotube composites (PDMS/CNT) to obtain the lightweight and absorption-type microwave shielding composites. The microwave absorption of Ag-Co-HM and the microwave shielding effectiveness (SE_T) of the PDMS/CNT/Ag-Co-HM composites was evaluated and discussed. The Ag-Co-HM with a molar ratio (Co/Ag) of 2.07 exhibited a low reflection loss as -46.6 dB at a thickness of 2.6 mm, and an effective absorption bandwidth of 8.40 GHz. The SE_T of the PDMS/CNT composites was greatly enhanced by the incorporation of the Ag-Co-HM. Furthermore, the absorption coefficient (A) was also improved by adding the Ag-Co-HM and was much higher than the reflection coefficient. The composites exhibited absorption-type microwave shielding composites. For example, the average microwave SE_T of 59.4 dB and A value of 0.78 are achieved in the PDMS/CNT/Ag-Co-HM composites containing 5 wt% CNTs and 10 wt% Ag-Co-HMs, which are much higher than the corresponding values of 33.7 dB and 0.63 in the PDMS/CNT composites with only 5 wt% CNTs. In addition, the hollow structure of Ag-Co-HM endows the PDMS/CNT/Ag-Co-HM composites to have a low density.

Key words: Microwave shielding, Absorption loss, Lightweight, Polydimethylsiloxane, Carbon nanotube