The preparation of yolk–shell microwave absorption materials with low density and excellent microwave absorption property requires reasonable design and economical manufacture. In this study, an efficient strategy without any templates or reducing gases has been designed to fabricate multi-core yolk–shell Co@C nanospheres by high temperature carbonization. The results showed that Co3O4 was completely reduced by the carbon shell to metal cobalt at temperatures above 750 °C. This unique multi-core yolk–shell structure with shell of 600 nm and multiple cores of tens of nanometers can provide sufficient interface and space to reflect and scatter electromagnetic waves. At the same time, the metal cobalt layer and carbon layer provide magnetic loss ability and dielectric loss ability, respectively, making the composite show good wave absorption performance. The minimal RL value of samples carbonized at 750 °C reaches −40 dB and the efficient absorption band reaches 9 GHz with the thickness ranges from 2–9 mm. Therefore, this is a facile, effective and economical strategy to prepare yolk–shell structure, which provides a new idea for the preparation of microwave absorption materials.
A MoSi2 coating layer with a MoB protected layer was simply prepared by using a combined method, which involved slurry painting and an embedded method via a hot press sintering process. The microstructure and phase composition of the coatings were investigated and determined.
The experimental time and the B addition are considered as important factors to be discussed in this study. All the results proved that when B is added, it was found that the formation of MoB played an important role of a diffusion barrier to Si and hindered the production of the poor oxidation
resistance phases (Mo5Si3 and Mo3Si).
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