| This paper is mainly focuses on the research progress and synthesis routes of W-type ferrites and modified absorbers.Through the understanding of the current research progress,we find that the improvement of the preparation method,surface modification and combination of wave-absorbing materials are significant for improving the microwave absorbing properties.The basic reaction of the sol-gel self-propagation method is carried out in solution,which can reach the level of molecular mixing and the auto-ignition reaction avoids high-temperature pre-burning,reducing the chance of hard agglomeration.Therefore,it is better than other routes in the preparation of ultrafine ferrite.According to the literature review,there is no literature on the use of citric acid(CA)and ethylenediaminetetraacetic acid(EDTA)as compound chelating agents,ethylene glycol(EG)as a dispersant for the preparation of W-type hexagonal ferrites.In the work of this paper,a modified sol-gel self-propagating method is used to synthesis W-type strontium-manganese ferrites.At the same time,surface oxidation treatment of 430L alloy powders.Then,we use the blending method compounded the modified carbonyl iron powder with magnetic W-type ferrite and conductive polyaniline(PANI),respectively.Subsequently,a series of characterization methods are used to test and analyze the phase composition,surface morphologies and electromagnetic parameters of the target samples.According to the electromagnetic datas,the curve of the reflection loss versus frequency of the prepared samples in the 2-18 GHz range is simulated.Thus,a novel composite wave-absorbing material with good impedance matching performance and excellent wave-absorbing performance is prepared.The specific inquiry contents and conclusions are summarized as follows:(1)Using CA and EDTA as composite complexing agents,ethylene glycol(EG)as dispersant,ammonia was used to adjust the pH of the solution to synthesize single-phase SrMn2Fe16O27(SrMn2-W)absorbers.The process conditions were optimized to explore the influence of iron content,the complexing agent EDTA and CA ratio,initial pH value,dispersant content,sintering temperature and sintering time on the synthesis of pure phase SrMn2-W ferrite.The optimum process conditions for the preparation of pure W-type were as follow:The iron content was 15.6,the chelating agent ratio of EDTA and CA was 1:1.1,the pH value of the solution was approximately neutral,a certain amount of ethylene glycol was added,the temperature was maintained at 450 ? for 3 hours and 1050 ? for 5 hours.The preliminary wave-absorption test was performed on the prepared ferrite.The results showed that the maximum reflection loss at 16.64 GHz was 29.41 dB when the material thickness was 5 mm.The frequency range of greater than 10 dB was from 4.24 to 6.08 GHz and 15.76 to 17.6 GHz,and the bandwidth was 3.68 GHz.(2)Surface oxidation of magnetic alloy micropowders were performed.The results of XRD and oxidative weight gains indicated that the optimal temperature and time for the high temperature oxidation of 430L alloy powders were 900 ? and 3 h,respectively.The electromagnetic properties before and after treatment were characterized,and the effects of the oxidation treatment on its parameters were analyzed to further simulate the microwave absorbing properties.From the experimental results,it could be seen that after the oxidation treatment,the real value of the dielectric constant of the alloy decreased significantly,and the magnetic properties also changed.However,the impedance matching after processing was better.When the test thickness was 2 mm,the oxidation-treated alloy powders had a frequency range of greater than 10 dB from 9.6 to 14.56 GHz,a maximum reflection loss was 22.58 dB at 11.8 GHz,and the absorption bandwidth was 4.96 GHz.(3)The modified carbonyl iron powder and the W-type ferrite were compounded into a composite absorber by means of mechanical blending method.It was confirmed by XRD and infrared test data that there were both W-type ferrite and carbonyl iron in the composite material.According to the microwave absorption test,when the thickness was 1.5 mm,the composite material had a minimum reflection loss value was-27.30 dB at 14.16 GHz and a reflection loss of less than-10 dB with a bandwidth was 7.44 GHz.Overall,the microwave absorption performance of the composites material was wider than that of single W-type ferrite or carbonyl iron powder,and the absorption band was enhanced.(4)Different amounts of PANI/MZ were compounded to prepare electromagnetic composites,and the influence of coating methods on the microwave absorbing properties was studied.The results of microwave absorption performance test indicated that the composites prepared by chemical blending with the mass fraction of 10%PANI had better microwave absorbing properties.At a test thickness of 1.5 mm,the reflection loss of the composite product at 14.24 GHz had a maximum value was 29.62 dB with a bandwidth was 7.10 GHz. |
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