The Design And Synthesis Of Fe-based Mocrowave Absorbing Composite Materials With Heat Stability And Its Performance Study

With the electromagnetic wave technology developed rapidly and employed at home and abroad widely,the problems of EM interference,EM pollution and EM signal leakage had brought unprecedented risks in people's daily production and lives,even threatening physical health of human.Recent years,in order to solve the problems of electromagnetic wave,electromagnetic absorption had attracted a lot of interest widely.Carbonyl iron,as a commercially available magnetic metal,is one of the most promising candidates for high-performance microwave absorbing materials with great application prospect,but carbonyl iron had poor heat stability.The article was through designing and fabrication of Fe-based composites to overcoming the poor thermal stability of carbonyl iron and further exploring their microwave absorption performances.In this paper,four Fe-based composites of Fe@AlPO₄,Fe@C,Fe@SiO₂,Fe@SiO₂@ZrO₂ were designed and synthesized.The results showed that carbonyl iron had poor thermal stability,so the saturation magnetization?Ms?of carbonyl iron decreased greatly after the process of heat treatment in air.Meanwhile,the complex permittivity and permeability of carbonyl iron decreased greatly during high temperature treatment,indicating high temperature damaged its dielectric and magnetic properties.Compared with carbonyl iron,the four functional layers prevented the core material of Fe from oxidation to some degree and improved the thermal stability of Fe-based composites,the Fe@AlPO₄ composite showed excellent heat stability.Moreover,the complex permittivity and permeability of Fe@AlPO₄ composite declined slightly after heat treatment,thus Fe@AlPO₄ composite showed better microwave absorption performance than carbonyl iron.There AlPO₄ layer has been innovatively optimized further and deposited on the surface of carbonyl iron so as to explore the effect of coating content on the thermal stability and microwave absorption performance.It is found that AlPO₄ layers in the composites not only improve the anti-oxidative ability of the internal carbonyl iron significantly,but also adjust its electromagnetic parameters,resulting in the good matching of characteristic impedance.With the optimized content of AlPO₄ layer,Fe@AlPO₄-4 composite could display excellent reflection loss characteristics reaching the-39.9 dB at 5.4 GHz,where the effective absorption in a very broad frequency range of 15.6 GHz?2.4-18.0 GHz over-10 dB?can be achieved when the thickness of absorber was from 1.0 mm to 5.0 mm.The microwave absorption performance of Fe@AlPO₄ composite was indeed superior to pure carbonyl iron,as well as many carbonyl iron-based composites ever reported.More importantly,Fe@AlPO₄ composite further presents durable performance after being treated at high temperature for a long time of 24 h and 48 h.These results provide a new insight to fabricate carbonyl iron-based composites with both good microwave absorption and anti-oxidative ability to meet the requirements in practical applications.