Adjusting the microwave absorption properties of carbon nanotube composites with ferrocene by annealing under different conditions

Carbon composites with magnetic metal nanoparticles are promising high-performance microwave absorbers with both dielectric loss and magnetic loss. Ferrocene has been sublimed into the evacuated multi-walled carbon nanotubes (MWCNTs) and then annealed under different atmosphere to obtain different structures with different microwave absorption features. A large amount of Fe₃C Yolk-shell structures with a small amount of low encapsulated Fe₃C@MWCNTs have been obtained after annealing at hydrogen atmosphere. A large amount of highly encapsulated α-Fe@MWCNTs and rod-shaped structures composed of Fe₃C nanoparticles with a small amount of Fe₇C₃@MWCNTs have been produced after annealing under ferrocene atmosphere. The structures have been characterized by transmission electron microscope, Raman, and X-ray diffraction. The maximum reflection loss of the as-produced Fe₃C yolk-shell structures with a small amount of Fe₃C@MWCNTs was measured to be up to −35.1 dB at 10.48 GHz with a thickness of 2 mm. The reflection loss values were detected to be less than −10 dB in the range of 8.9–11.4 GHz. However, multiple absorption bands have been observed by sample annealing under ferrocene atmosphere at 4.5, 9.4, 13.4 GHz with corresponding reflection loss values of −3.1, −4.8 and −12.6 dB with a thickness of 2 mm, respectively. The microwave absorption properties have been demonstrated to be significantly affected by the annealing atmospheres and temperatures.