FeNi alloy and nickel ferrite codoped carbon hollow microspheres for high-efficiency microwave absorption.

Composite particles with multiple components and specific structures are promising microwave absorbents due to their excellent and easily tailored synergism of multiple dissipation mechanisms and good impedance matching, but their design and highly efficient preparation remain as big challenges. In the present work, novel composite carbon–FeNi alloy–nickel ferrite hollow microspheres with a thin shell were constructed through a highly efficient spray drying–calcination route. The amorphous carbon serves as the matrix of the shell, and the FeNi alloy and nickel ferrite form an embedded structure in the carbon shell. The design of this matrix–dual dispersion phase structure not only enables the synergism between the magnetic loss of the magnetic dispersion phase and the dielectric loss of the carbon matrix, but also brings multiple reflection and scattering, interface polarization as well as an appropriate impedance matching. Due to these features, the hollow microspheric product presents excellent microwave-absorbing properties related to the processing conditions (the optimized effective absorption bandwidth reaches 7.76 GHz at a thickness of 2.04 mm). The hollow microspheres reported here are a promising candidate for a microwave absorbent with low density and strong dissipation. [ABSTRACT FROM AUTHOR]