Anti-Oxidation Treatment Of Carbonyl Iron Powders And Its Microwave Absorption Properties

With the rapid development of the air force and the high speed of aircrafts,the temperature of aircraft skin increases due to the friction between the air and the surface of aircraft.Therefore,microwave absorption materials should satisfy the high temperature and oxidation resistance demands.Carbonyl iron particles（CIPs）have the potential of application in the field of oxidation resistance and microwave absorption at high temperature.That is due to its high Curie temperature（770℃）,high magnetic saturation intensity,large magnetic loss and wide absorption bandwidth in the same thickness.In this paper,the oxidation resistance and microwave absorption properties of CIPs were improved by surface oxidation,inorganic coating and mechanical ball milling.Firstly,SiO₂ coated CIPs were fabricated by Stober method.Thermogravimetric analysis（TGA）shows that the SiO₂ coating layer can prevent the raw CIPs to contact with oxygen and increase the onset temperature of oxidation to 330℃.Compared with the raw CIPs,the permittivity of SiO₂ coated CIPs decreases.In addition,the permeability of SiO₂ coated CIPs and raw CIPs are almost the same.The reflection loss（RL）curves indicate that the RL values of the SiO₂ coated CIPs slightly reduce and the microwave absorption peaks move towards high frequency band.The bandwidth of RL values exceeding-10d B reaches 3.045GHz for the absorber with a thickness of 2.3mm,which is wider than that of the raw CIPs under the same conditions.Therefore,the SiO₂ coated layer not only enhanced the oxidant resistance property of raw CIPs but also improved its microwave absorption property.For better anti-oxidation properties,the bluing CIPs were fabricated by chemical plating with a bluing agent.TGA shows that the anti-oxidation property of bluing CIPs is better than that of the raw CIPs.After bluing CIPs,the permittivity decrease and the real part of permeability is unchanged.In addition,it is significant that the imaginary part of permeability of bluing CIPs decreases.That will decrease the microwave absorption properties of bluing CIPs.Compared with the peaks RL of the raw CIPs,there is no significant increase.On the other hand,the microwave absorption peaks of bluing CIPs move towards high frequency band and the bandwidth becomes smaller.Therefore,the further study about better oxidation-resistance microwave absorption materials is needed.Finally,high-energy ball milling,bluing flake CIPs and SiO₂ coated bluing flake CIPs was used to improve microwave absorption and anti-oxidation properties of the bluing CIPs.TGA shows that the anti-oxidant property of SiO₂ coated bluing flaky CIPs is the best of raw CIPs,flaky CIPs and bluing flake CIPs.After high-energy ball milling,the imaginary part of permeability and magnetic loss of the flake CIPs increase.The microwave absorption property of flake CIPs is better than that of raw CIPs.However,the oxidation resistance of flake CIPs is worse than that of the raw CIPs.The impedance matching of bluing flake CIPs decrease due to the enhancement of permittivity.Thus,the microwave absorbing properties of raw CIPs are better than that of bluing flake CIPs.However,the oxidation resistance of bluing flake CIPs is better than raw CIPs and flake CIPs.The SiO₂ layer can reduce the permittivity of SiO₂ coated bluing flaky CIPs and improve the impedance matching.The RL peak value of Si O₂ coated bluing flaky CIPs is-20.74dB for the absorber thickness of 2.0mm.It is better than that of bluing flake CIPs and raw CIPs.In conclusion,SiO₂ coated bluing flake CIPs is a kind of excellent oxidation-resistance microwave absorption material.