Research On Corrosion Failure Mechanism And Protective Mechanism Of Carbonyl Iron Powder

As a traditional ferromagnetic absorber,carbonyl iron powder has strong magnetic loss characteristics with high permeability and high saturation magnetization.,which make it become one of the most widely used magnetic absorbers in electromagnetic radiation control filed.However,due to its high surface activity,it is prone to corrosion when exposed to harsh environments such as high humidity,high temperature,and salt spray,resulting in deterioration in electromagnetic absorption performance.For instance,in a marine environment,the corrosion of carbonyl iron magnetic absorbents can lead to the aging and detachment fault of coatings on the surfaces of warships or submarines,resulting in a significant decline in microwave absorption performance.Therefore,it is of great practical significance to carry out research on iron-based magnetic absorbents with excellent corrosion resistance and microwave absorption properties.The corrosion failure behavior patterns and protective mechanisms of carbonyl iron powder were investigated in this thesis.Based on first-principles calculations and microstructure evolution,the corrosion mechanisms of carbonyl iron powder were elucidated,and the diffusion model of corrosive particles was constructed.The technical idea of utilizing low surface energy organic substances to construct a non-wetting protective layer was proposed.The contact between carbonyl iron powder and corrosive particles was effectively inhibited by the protective layer,and the corrosion resistance of carbonyl iron powder electromagnetic wave absorbers was significantly improved.The main research contents of this thesis are as follows:1.The evolution model for the corrosion process of carbonyl iron powder was constructed.The relationship between electron work function,electron escape,migration and corrosion on the surface of metal Fe was elucidated by employing first-principles methods.Combined with the effects of salt spray corrosion environment on the microscopic characteristics of carbonyl iron powder,the degradation mechanism of the structure and composition evolution of carbonyl iron powder on the electromagnetic properties was clarified.On this basis,an interaction model based on molecular dynamics simulation of the dynamic diffusion behavior of low surface energy protective materials and corrosive particles was proposed,which provides theoretical guidance for the corrosion protection design of carbonyl iron powder.2.A method was proposed for constructing a non-wetting protective layer on the surface of carbonyl iron powder by using chemical vapor deposition.The carbonyl iron/parylene-C composite structure was synthesized by utilizing low surface energy organic parylene-C as precursor,which improved the corrosion resistance of carbonyl iron powder.The anti-corrosion mechanism of the non-wetting protective layer was elucidated through characterization of corrosion behavior and analysis of electromagnetic parameters.An internal correlation was established between the protective layer structure and the electromagnetic properties of carbonyl iron powder,which laid an experimental foundation for the development of corrosion resistance wave-absorbing iron-based magnetic absorbent.3.The anti-corrosion technology was proposed based on chemical bonding to prepare a non-wetting protective layer.Aiming at the problem where the bonding strength achieved by chemical vapor deposition falls short of the demands for long-term corrosion resistance,and recognizing the adverse effects of the structure of parylene-C protective layer on electromagnetic performance,the carbonyl iron/fluorosilane composite structure was synthesized via using sol-gel method.Based on the high hydrophobicity and shielding characteristics of the protective layer,the corrosion rate decreased significantly by three orders of magnitude,and the protection efficiency was as high as 99.21%.Simultaneously,the electromagnetic absorption characteristics were substantially retained,which meets the fundamental requirements for both anti-corrosion and wave absorption of carbonyl iron powder absorbent.4.A design method of active-passive integrated multi-functional protective layer was proposed.In view of the current passive protection status of a single non-wetting protective layer,based on the active protection principle that the corrosion inhibitor can coordinate with the metal Fe,a non-wetting active protective layer was innovatively prepared via using the corrosion inhibitor and the low surface energy material organosilicon.Under the premise that the electromagnetic properties of the carbonyl iron powder remain basically unchanged,the excellent corrosion resistance effect for up to480 h in salt spray corrosion environment was achieved,which laid a solid foundation for advancing the creation of high-performance electromagnetic wave absorbing materials which are capable of long-term corrosion resistance.In this thesis,the corrosion mechanism of carbonyl iron powder was deeply explored from the microscopic perspective,and the corrosion resistance mechanism of non-wetting protective layer composite structure was clarified.The theoretical system of anticorrosion of iron-based magnetic absorbent was developed and enriched,which offers valuable reference significance for the research on corrosion protection of metal micropowders.