Preparation And Properties Of Microwave Absorbing Materials With Temperature-resistant Resin Matrix

With the development of stealth technology and the requirement of stealth performance at high temperature of weaponry,the traditional characters including thin thickness,broad band,low density and strong absorption of radar microwave absorbing materials cannot satisfy fully needs of new generation air weapons.The research of radar wave absorbing materials with both perfect absorbing and temperature resistant performance has draw more and more attention all over the world.Microwave absorbing coating has been widely studied due to its good adaptability to the shape of parts,simple construction and good applicability to existing weapons equipment,what's more important is that it has less less influence on the firepower and motility of weapon system.Almost all of researchers focus on microwave absorbing coating used at room temperature.There is rare data on absorbing coating used at higher temperature.Carbonyl iron particle?CIPs?,as a typical magnetic loss microwave absorbing materials,is one of the most commonly used radar microwave absorber for the moment.It could be used as one of temperature resistant absorber for that its Curie temperature can be as high as 770?.The main researches and results are as follows:?1?CIPs/Silicone?SI?resin microwave absorbing coatings were prepared by spraying.Its electromagnetic parameter can be tuned by adjusting the content of CIPs and its absorbing property is tuned by adjusting the thickness of coating.The reflectivity of the CIPs/SI resin microwave absorbing coatings did not show significant change as temperature arrange from RT to 300?,which shows good thermal stability.Both the real and imaginary part of permittivity of CIPs/SI resin microwave absorbing coating show obvious improvement after heat treatment for that O2 in the air can promote the reaction between CIPs and SI resin.Meanwhile,both the real and imaginary part of permeability of the coating show obvious reduce after heat treatment because of particial oxidation of CIPs.CIPs/Polyimide?PI?resin and CIPs/Boron phenolic-formaldehyde?BPF?resin microwave absorbing coatings were prepared by hot-pressing method.Comparing the adhesive strength between absorbing coatings and Ti alloy matrix as well as thermal stability of the three kind of coatings with heat treatment at different temperature,boron phenolic resin as matrix show the best performance.However,in view of preparation technology of the three kind of resin matrix,SI resin was chosed as the temperature-resistant matrix to further research.?2?Y₂Mo₃O₁₂ precursor was prepared by citric acid method with yttrium nitrate and ammonium molybdate.The TG-DSC curve of Y₂Mo₃O₁₂ precursor shows that best calcining temperature of the precursor is 780?,at which we can get Y₂Mo₃O₁₂ particles with high purity,good crystallinity and good uniformity on grain size.The Negative thermal expansion?NTE?coefficient of Y₂Mo₃O₁₂ between 100? and 800? is-10.4×10-6/?,which is shown by high temperature XRD test.Y₂Mo₃O₁₂/CIPs/SI resin microwave absorbing coating was prepared by dispersing Y₂Mo₃O₁₂ particles and CIPs into silicone resin.The thermal expansion coefficient and microwave absorbing property of Y₂Mo₃O₁₂/CIPs/SI resin microwave absorbing coatings with different content of Y₂Mo₃O₁₂.As the content of Y₂Mo₃O₁₂ increases,the thermal expansion coefficient of the coating reduces and both the real and imaginary part of permittivity increase,while both the real and imaginary part of permeability decrease.What's more,the frequency corresponding to minimum reflectivity of coating shifts to higher frequency with the content of Y₂Mo₃O₁₂ increasing.The thermal stability of Y₂Mo₃O₁₂/CIPs/SI resin microwave absorbing coating with 10wt% content Y₂Mo₃O₁₂ particles was researched.The thermal stability of Y₂Mo₃O₁₂/CIPs/SI resin microwave absorbing coating shows little change comparing to that of CIPs/SI resin coating.The absorption value of Y₂Mo₃O₁₂/CIPs/SI resin microwave absorbing coating also turns rise as the heat treatment temperature increase.?3?Fe₃O₄@CIPs were obtained by bluing process at high temperature with CIPs.The Fe₃O₄@CIPs with different processing time were analysised.It shows with the increase of processing time,the content of Fe₃O₄ particles gains obviously and the oxidative stability of Fe₃O₄@CIPs will be better.The study of electromagnetic parameters and absorbing property of Fe₃O₄@CIPs/SI resin microwave absorbing coating shows that with the increase of processing time,the real part of permittivity slightly decrease but the imaginary part change little and it is the same as permeability.What's more,the frequency corresponding to minimum absorption of coating shift to higher frequency.After heat treatment for 100 hours at 150? and 200?,respectively,the oxidative stability of Fe₃O₄@CIPs/SI resin absorbing coating with bluing time for 90 min shows better than the oxidative stability of coating with untreated CIPs.It can be attributed to the Fe₃O₄ particles formed on the surface of CIPs after bluing process.The Fe₃O₄ particles formed on the surface of CIPs prevent the diffusion of O2 at high temperature.However,Fe₃O₄@CIPs still can not be used as microwave absorber at 250? for a long time.?4?Co@CIPs were prepared by electroless plating method.TG curve shows that the thermostability of Co@CIPs is better than that of untreated CIPs.However,processing time of electroless plating has no obvious influence on the thermostability.The study of electromagnetic parameters and absorbing property of Co@CIPs/SI resin microwave absorbing coating shows that,comparing to the electromagnetic parameters of CIPs/SI resin coating,both the real and imaginary part of permittivity increase,and the real part of permeability decrease slightly while the imaginary part of permeability is almost invariable.What's more,the frequency corresponding to minimum absorption of coating shift to lower frequency.With the increase of processing time,both the real and imaginary part of permittivity continuingly increase and the real part of permeability continuingly decrease.Co@CIPs/SI resin coating made of Co@CIPs prepared by electroless plating method for 1 hour were heated at 250? for 100 h to be researched.It shows that Co layer has important influence on CIPs/SI resin coating under heat treatment at 250? for that the electromagnetic parameter of Co@CIPs/SI resin coating is almost invariable while that of CIPs/SI resin coating has obvious change after heat treatment.All these shows that Co@CIPs are good thermostability.?5?SiO₂@CIPs were obtained by Stober method.TG curve shows that the thermostability of Si O2@CIPs is better than that of untreated CIPs.The study of electromagnetic parameters and absorbing property of SiO₂@CIPs/SI resin microwave absorbing coating shows that,comparing to the electromagnetic parameters of CIPs/SI resin coating,both the real and imaginary part of permittivity decrease slightly and it is the same as permeability.What's more,the frequency corresponding to minimum absorption of coating shift to higher frequency.The broadened absorbing frequency of SiO₂@CIPs/SI resin coating can be ascribed to SiO₂ layer,which increase the impedance matching.It shows that SiO₂ layer has important influence on CIPs/SI resin coating under heat treatment at 250? for that the electromagnetic parameter of SiO₂@CIPs/SI resin coating is almost invariable while that of CIPs/SI resin coating has obvious change after heat treatment.All these shows that SiO₂@CIPs have good thermostability.