Study On Surfactant Modified Carbonyl Iron Powder And Its Corrosion Resistance

Carbonyl iron powder,as an important microwave absorbing material,has the advantages of high magnetic loss,specific saturation magnetization and Curie temperature,and is widely used in industrial,military and medical fields.However,because carbonyl iron powder is relatively active,it is easy to corrode when it is used in a high temperature and humid environment.This phenomenon will seriously weaken the magnetic properties of carbonyl iron powder,resulting in the decline or even failure of its wave absorbing ability.Therefore,it is very important to improve the corrosion resistance of carbonyl iron powder so that it can maintain good physical and chemical properties in complex and harsh application environments.Surface coating modification technology is an effective means to improve the corrosion resistance of metal powders.In this thesis,to address the shortcomings of poor corrosion resistance of carbonyl iron powder,the surface of carbonyl iron powder was first modified by using surfactants to introduce reactive groups on the surface of carbonyl iron powder,and further condensation reaction occurred between the terminal hydroxyl group of poly(dimethylsiloxane)(PDMS)and the reactive groups on the surface of carbonyl iron powder to form a coating layer on its surface.On this basis,the influence of the main process parameters on the microstructure,contact angle,thermal stability,corrosion resistance and electromagnetic properties of the powder was systematically studied.The main contents and innovations of this thesis can be summarized as follows:(1)The mechanism of surface modification of carbonyl iron powder by cationic surfactant cetyltrimethyl bromide(CTAB),anionic surfactant sodium dodecylbenzene sulfonate(SDBS)and amphoteric surfactant glycine(Gly)was investigated.A comprehensive comparison of the effects of the three surfactants on the powder microscopic morphology,contact angle,thermal stability,corrosion resistance and electromagnetic properties was conducted,and it was concluded that the comprehensive performance of the amphoteric surfactant modified carbonyl iron powder was better.(2)Carbonyl iron powder was treated with glycine surfactant.Under the optimal process parameters,the surface of carbonyl iron powder was successfully grafted with active groups(-NH₂).At the same time,the thermal stability and corrosion resistance of the grafted powder have also been greatly improved:the oxidation weight gain temperature is increased to about 350°C,and the corrosion current density is reduced to9.968×10-~6A/cm~2.The maximum return loss at 5.23GHz is-47.10d B.(3)The modified carbonyl iron powder was coated with PDMS.Under the optimal process parameters,the thermal stability and corrosion resistance of the coated powder are greatly improved:the oxidation weight gain temperature is increased to about 400°C,and the corrosion current density is decreased to 9.818×10^-7A/cm~2.The maximum reflection loss of the coated powder at 4.44GHz is-34.96d B.The final powder prepared in this thesis has excellent corrosion resistance and thermal stability as well as good wave absorption properties.