High-temperature Electromagnetic Properties Of Nd₂Co₁₇ And FeCo Micronized Ceramic Composites

With the continuous development and application of electromagnetic wave technology,electromagnetic interference and electromagnetic radiation have gradually become another major source of pollution in the 21st century,which has brought a great threat to human life and health.Therefore,it is crucial to develop the materials with electromagnetic shielding and microwave absorption properties.Meanwhile,with the research and development of stealth technology,microwave absorbing materials are gradually used in the military field.And the demand for high-temperature microwave-absorbing materials is becoming more and more urgent.At present,the materials developed abroad for high temperature absorption are mainly Si C-based oxygen-free ceramic materials and carbon-based absorbers,which are mainly dielectronic type absorbers.Although these materials have the advantages of better oxidation resistance,high temperature resistance and low density,they have the problems of excessive coating thickness and narrow absorption band.In order to solve the problems,magnetic metal materials with high saturation magnetization and high Curie temperature are gradually getting into the researchers'view.Magnetic metal materials have higher permeability compared with dielectric materials and can significantly reduce the thickness of microwave absorbers.In this paper,we chose Nd₂Co₁₇ alloys with high Curie temperature and high saturation magnetization for the study,and had prepared Nd₂Co₁₇ micro powder by using arc melting,annealing,water quenching,mortar grinding and ball milling.The electromagnetic parameters and the absorption properties in X band of Nd₂Co₁₇ micro powder/polyurethane composites with different volume fractions were investigated.When the volume fraction of the composite is 27.5%and the thickness is 1.5 mm,The Nd₂Co₁₇ micro powder/polyurethane composite has good microwave absorption performance in X band.In order to improve the oxidation resistance and high-temperature stability of Nd₂Co₁₇ micro powders,we had prepared the Nd₂Co₁₇@C/Na₂Si O₃ high-temperature composite by surface oxidation,carbon coating and sodium silicate composite treatment of Nd₂Co₁₇ micro powders.The experimental results show that the composite can achieve the absorption performance below-6 d B in the whole X band at a thickness of 1.5 mm after heating up to 450?,and the thickness of the absorber is substantially reduced compared to the pure dielectric material.In order to reduce the preparation cost,Fe Co50 alloy micronized powder(The atomic ratio of Fe and Co is 1:1)with high Curie temperature and high saturation magnetization was used as raw material in this paper to prepare Fe Co50 micronized powder/polyurethane composites with different volume fractions.When the volume fraction is 38%and the thickness is 1.12 mm,the effective absorption bandwidth(RL<-10 d B)can cover the whole X band.After antioxidant treatments,the Fe Co50@C/Na₂Si O₃ composite was prepared.When the thickness of the composite is1.3 mm,its effective absorption bandwidth(RL<-10 d B)at 500°C can basically cover the whole X band.Meanwhile,we prepared easy-planar Fe Co50 micronized powder/polyurethane composites with different volume fractions.When the volume fraction of the composite is 40%and the thickness is 1.65 mm,the composite has the best microwave absorption performance in the S band.After antioxidant treatments,the easy-planar Fe Co50@C/Na₂Si O₃high-temperature composite is prepared and the RL in the S band at 500°C is basically below-4 d B.