Synthesis Of Shell Structured Ferromagnetic Absorbers And Corrosion Resistance Mechanism

The rapid development of electronic technology has continuously enriched electronic devices and brought convenience to human life.At the same time,it also brings a large number of electromagnetic radiation pollution to the human living space and threatens human physical and mental health.Magnetic metal absorbing materials?MMAMs?can effectively avoid electromagnetic radiation due to the good microwave absorption performance,thus attracts extensive attention.Moreover,MMAMs play an important role in anti-reconnaissance and stealth in the field of military defense.However,MMAMs face severe corrosion bottlenecks?chemical corrosion and electrochemical corrosion?when applied in high-temperature environment?hot end parts of engines or kinetic bomb surfaces,etc.?and marine?carrier-based aircraft or ship,etc.?.For this reason,it is particularly urgent to develop the composite structure for magnetic metal that have both high absorption performance and good corrosion resistance in high temperature and marine environments.In this dissertation,FeSiAl alloy?FSA?is used as the carrier,which aiming at solving the corrosion bottleneck of MMAMs in high temperature?>300??and marine environments.The high temperature oxidation and electrochemical corrosion mechanisms of FSA are explored through thermodynamics,thermal analysis kinetics,Raman spectroscopy and X-ray photoelectron spectroscopy?XPS?depth profiling techniques.The corresponding corrosion model is constructed from the perspectives of the microstructure and interface.The FSA multi-shell composite structure is prepared by means of plasma induction technology,surface grafting method,St?ber process and catalytic vapor deposition?CCVD?.On the basis of satisfying the coupling between the performance,bonding strength and expansion coefficient,the multi-shell composite structure shows good microwave absorption performance,and solves the corrosion problem of FSA under high temperature and marine environment.The research contents and innovations of this dissertation are listed as follows:1.In order to meet the needs of high temperature stealth design and application of Magnetic metal materials?MMMs?,the chemical corrosion?high temperature oxidation?behavior of FSA micropowder(D₅₀?46?m)is studied in high temperature environment.By annealing the FSA micropowder at 500? in the air for 1?24 h,the evolution law of the surface oxidation state for FSA is revealed based on the thermodynamic analysis.Subsequently,thermal analysis kinetics are used to explore the high-temperature oxidation behavior of FSA micropowder,clarifying its solid and liquid oxidation stages,revealing the oxidation rate of FSA micropowder increased sharply with the increasing temperature and constructing of a non-isothermal oxidation kinetic model for the solid-state oxidation stage.It has a certain guiding role for the high-temperature anti-oxidation strategy of MMMs.2.Regarding the phenomenon that the oxidation rate of FSA micropowder increases sharply with the increasing temperature,we combine the difference of the vapor pressure for the different material,and innovatively use plasma induction technology to induce and synthesize the anti-oxidation ceramic layer with a thickness of ?400nm?Gradient ceramic layers,GCLs?on the surface of FSA.FSA@Al₂O₃@SiO₂ multi-shell composite structure?FSA@GCLs?not only ensures the high-strength bonding between Al₂O₃,SiO₂and FSA,but also achieves the thermal expansion matching between Al₂O₃ and SiO₂.Compared with the high temperature oxidation resistance and microwave electromagnetic parameters of FSA@GCLs,it is found that FSA@GCLs has the excellent high temperature oxidation resistance under extreme conditions.The initial oxidation temperature is as high as 1279?,which is 140? higher than that of pure FSA.Due to the synergistic effect of the magnetic-dielectric loss of FSA,SiO₂ and Al₂O₃,the absolute absorption bandwidth of FSA@GCLs is up to 7.33 GHz?RL<-10 dB?when the matching thickness is 2.5mm.Plasma induction technology is of great significance for solving the problem of high temperature oxidation resistance of MMAMs.3.Based on the application background of MMMs in the marine,we choose the smelting method to make FSA cylindrical.Through Raman spectroscopy and XPS depth profiling technology,the corrosion products of the FSA surface are respectively revealed over time in salt spray environment with the generation of C=O bond and?-FeOOH over time and the change law of Fe⁰?Fe²⁺?Fe³⁺in depth.It shows the dynamic corrosion process of FSA in salt spray environment.In combination with electrochemical corrosion kinetics,the corrosion kinetic parameters of FSA in 5wt%NaCl solution were characterized by electrochemical tests.The Corrosion Rate?CR?and corrosion current(i_corr)increases from 2.99×10^-12 m/s and 1.65×10^-5 A.cm^-2 to 5.85×10^-12 m/s and 3.23×10^-5 A.cm^-2 with the increase of FSA immersion time in NaCl solution from 1 h to 48 h.4.Due to the increasing corrosion rate of FSA over time in salt fog environment,we modify flake high-barrier graphene oxide?GO?with good hydrophobicity and impermeability?except proton?to the surface of FSA(D₅₀?10.6?m)by the surface grafting method,and prepared FSA@GO/P composite structure.Comparing the electromagnetic parameters of FSA and FSA@GO/P,it is found that the permeability of FSA@GO/P is lower than that of FSA in 0.5?10 GHz,and the permittivity is higher.This phenomenon leads to the decrease of microwave absorption performance of FSA micropowder.In order to overcome the problem of poor impedance matching between the interface and free space caused by the higher conductivity of graphene oxide,we use amorphous carbon prepared by CCVD method to replace GO,and combine the St?ber process to prepare the FSA@SiO₂@C multi-shell composite structure.FSA@SiO₂@C realizes the matching and coupling between FSA,SiO₂ and C layers,reducing pure FSA corrosion rate from 2.66×10^-12 m/s to 1.52×10^-12 m/s and widening the microwave absorption bandwidth from 4.2 GHz to 5.84 GHz?the matching thickness is 3.0 mm?.FSA@SiO₂@C multi-shell composite structure demonstrates the good microwave absorption performance and corrosion resistance,and provides a feasible design idea for the electrochemical corrosion resistance of MMAMs.This dissertation dispalys the corrosion mechanism for high temperature oxidation and electrochemical corrosion of FSA in salt spray environment,and puts forward some new ideas to improve its the high temperature oxidation resistance and marine corrosion resistance.It has explored the referential technical paths for MMMs in high temperature and marine environment,and lays the theoretical foundation for the functional design and the application development of the composite structure for magnetic metal under different application requirements.