| In recent years,with the advancement of modern science and technology,the problem of electromagnetic interference has become increasingly serious,and microwave absorbing materials are an important way to solve this problem.Carbonyl iron powder（CIP）,as a typical magnetic metal material,has great application potential in the field of microwave absorption.However,CIP has shortcomings such as narrow absorption band,oxidation,and agglomeration,and it needs to be modified to overcome those shortcomings urgently.In this thesis,CIP@SiO2,CIP@SiO2@ZrO2 and CIP@void@ZrO2 microspheres were fabricated as model samples of the core-single-shell,core-double-shell,and yolk-shell absorbents.The combination of CIP and dielectric ceramic materials（SiO2 and ZrO2）not only enhanced the microwave absorption capacity of the composites which broadened the absorption frequency band,but also significantly improved the oxidation resistance of CIP which broadened the temperature range of the absorbing material.Firstly,at room temperature,the electromagnetic absorption performance of the as-prepared multicomponent hierarchical microspheres was superior to the sole CIP,owing to the combination of strong magnetic loss of CIP core and excellent dielectric loss of SiO2 and ZrO2 shell.Among them,CIP@void@ZrO2 had the best absorbing performance of all testing samples in this case,the special hollow cavity of the yolk-shell structure can improve the impedance matching performance and strengthens the multi-interface polarization loss and dipole orientation polarization loss effectively.the minimum RL of yolk-shell CIP@void@ZrO2 microspheres was up to-28.38 d B at the absorber thickness of 2.2 mm and the effective absorption bandwidth reach 7.44 GHz from 10.24 to 17.68 GHz at 2.1 mm thickness.For CIP@SiO2@ZrO2,the minimum RL was-20.69 d B at 17.44 GHz with a thickness of 1.7 mm and the effective absorption bandwidth can reach 6.48 GHz at the coating thickness of 2 mm.Secondly,we selected different oxidation temperature points to heat-treat CIP,CIP@SiO2,CIP@SiO2@ZrO2 and CIP@void@ZrO2 to evaluate the oxidation resistance of each sample.Through comprehensive comparison,it is found that CIP@SiO2@ZrO2 shown better antioxidant properties,the dense SiO2 shell and multi-layer structure played a key role in protecting the CIP magnetic core.The initial oxidation temperature of CIP@SiO2@ZrO2 was about 200℃ higher than that of CIP,When the heat treatment temperature reached 400℃,the bandwidth of CIP@SiO2@ZrO2 effective absorption band can still be maintained at 80%of that at25℃.However,the less dense ZrO2 layer has limited improvement in the oxidation resistance of the sample,and the retention rate of the effective absorption frequency band of CIP@void@ZrO2 had dropped significantly at 400℃,which was only 57.4%of that at 25℃.In summary,the yolk-shell CIP@void@ZrO2 had better absorption performance at room temperature due to the effective improvement of impedance matching by the yolk-shell structure and we believed that CIP@void@ZrO2 will be a strong competitor of high-performance absorbing materials.The core-double-shell CIP@SiO2@ZrO2effectively broadened the temperature range of carbonyl iron powder composite absorbing materials due to its good anti-oxidation properties. |
