Preparation And Absorption Properties Of High Entropy Oxide Powder

In recent years,with the development of microwave communication technology,the use of communication equipment is more and more frequent,seriously affecting human health,the resulting electromagnetic pollution problem is becoming more and more serious,absorbing materials become the focus of current research.However,the corrosion resistance,oxidation resistance and high temperature performance of conventional absorbing materials are not good,especially can not meet the stealth requirements of high temperature parts of weapons and equipment,which seriously limits the development of all-round stealth technology.Therefore,it is imperative to develop absorbing materials with high temperature resistance,corrosion resistance and oxidation resistance.High entropy ceramic materials are defined as solid solutions of five or more cationic or anionic sublattices with high configurational entropy.Although the absorption performance of high entropy ceramics is not good,compared with commonly used absorbing materials,high entropy ceramics have prominent advantages such as high strength,high hardness,corrosion resistance,wear resistance,oxidation resistance and high temperature resistance.In addition,the current research on high entropy absorbing ceramics is limited to a single temperature point,a single preparation method and its absorption properties,and the research system needs to be expanded.The influence of preparation technology on the characteristics of high entropy ceramic powder is also neglected.In this thesis,the effects of different preparation processes on the characteristics of high entropy oxide powder,and the absorption properties and high temperature stability of salt rock type and spinel type high entropy oxide powder were studied.The main research contents and results are as follows:（1）With oxide ceramic as the research system,based on the high entropy multicomponent synergy mechanism,(Mg_0.2Ni_0.2Co_0.2Cu_0.2Zn_0.2)O different precursors was prepared by the ball grinding（300 r/min,2 h）,titration（ammonia）and hydrothermal method（200℃,24 h）,The precursor powders were labeled S1,S2 and S3,respectively.The precursor powders were calcined at different temperatures（900℃-1200℃）to prepare the rock salt type high entropy oxide powders.Precursor can fire becomes(Mg_0.2Ni_0.2Co_0.2Cu_0.2Zn_0.2)O high entropy oxide powder under900℃,the higher the temperature phase,the more pure,pure single rock salt phase was achieved at 1200℃.SEM and XRD analysis show that the microstructure is related to the precursor,but the phase composition is independent of the precursor.All high entropy oxide powders present a single halite phase.Compared with S1 and S2,the high entropy oxide powder of S3 has uniform distribution on the surface of main crystal and fine grains.（2）The change ratio of raw material,using titration method in the preparation of rock salt high entropy oxide powder(Mg_0.1Ni_0.6Co_0.1Cu_0.1Zn_0.1)O and(Mg_0.15Ni_0.4Co_0.15Cu_0.15Zn_0.15)O under 1200℃,SEM and XRD showed that as the change of Ni element content,The relative positions of characteristic peaks of different high entropy ceramic powders change slightly,and the particle size becomes larger and larger.After testing and analysis with vector network analyzer,the wave absorption values of the salt type high entropy ceramic powder synthesized by three kinds of raw materials in 0-26 GHz are all within -10d B,indicating that the rock salt type high entropy oxide powder has poor electromagnetic wave absorption performance.But has a thermal stability,(Mg_0.2Ni_0.2Co_0.2Cu_0.2Zn_0.2)O high entropy oxide powder is stable under 1200℃.（3）The precursors of（MnCoFeNiZn）₃O₄,（MnCoFeNiCu）₃O₄and（MnCoFeNiCr）₃O₄were prepared by titration（ammonia titration）,and the spinel oxide powder was prepared by roasting at different temperatures（900℃-1200℃）.It was found that the minimum temperature of synthesized spinel type high entropy oxide powder（MnCoFeNiCu₃O₄）was 500℃.With the increase of sintering temperature,the grain size of（MnCoFeNiCu₃O₄）would first decrease and then increase because of agglomeration of sintered particles.When the sintering temperature reached 800℃,Good almost single cubic spinel phase was obtained.The high entropy oxide powder composed of（MnCoFeNiCu）₃O₄ has better magnetic properties and electromagnetic wave absorption than the other two components（MnCoFeNiZn）₃O₄ and（MnCoFeNiCr）₃O₄.（MnCoFeNiCu）₃O₄has the best electromagnetic wave absorption capacity at sintering temperature of 800℃,the minimum RL value is -15.5d B,and the bandwidth of RL lower than -10 dB can be adjusted by adjusting the thickness of the absorber（2.5-5.0mm）at 4-13 GHz broadband.It is a good electromagnetic absorbing material,stable at 1000℃.