Preparation And Properties Of MoSi₂ Composites As Microwave Absorbing Materials

MoSi₂ is one of the Dalton type?daltnide?intermetallic compounds with the largest amount of silicon in the Mo-Si system.Molybdenum atoms bind to each other by metal bonds,silicon atoms by covalent bonds,molybdenum and silicon atoms is between them.MoSi₂ has received considerable attention as a high-temperature structural material due to its metal bonding and covalent structural properties.The research focus of MoSi₂ is mostly on mechanical properties,but the electrical properties of MoSi₂,especially the feasibility of high temperature absorbent,are seldom studied.Compared with the traditional ferromagnetic absorbing materials,the research and preparation of MoSi₂ composite absorbing material is more valuable.In this experiment,MoSi₂ composite absorbing materials were prepared with MoSi₂ as wave absorbing agent,Al₂O₃ as matrix,SiO₂ as sintering additive,and B₂O₃,Cao,MgO as additives.The phase composition,microstructure,physical properties and dielectric properties of the samples sintered at different atmosphere,different sintering temperature and differden sintering Additive were characterized by X-ray diffractometer,scanning electron microscope andenergydispersive spectrum respectively.Which provides a theoretical basis for prepared MoSi₂ composite absorbing materials.The experimental study draws the following conclusions:?1?At 1200?,the fracture toughness,flexural strength,the real part and imaginary part of the dielectric constant of the composite materialsincrease with the change of sintering atmosphere from the air and the vacuum to the Ar atmosphere.The composites have more pores,owing to the phase being further oxidized to volatile MoO₃ at air atmosphere,which caused the fracture toughness and flexural strength of the material are the lowest;after sintering in Ar atmosphere,the MoSi₂ particles are coated with part of the Al₂O₃,which helps to improve the fracture toughness and flexural strength of the composites,the maximumvalue are 9.70 MPa·m^1/2 and 179.5MPa,respectively.?2?The addition of B₂O₃ did not change the phase composition of MoSi₂/Al₂O₃composites and significantly decreased the sintering temperature.By changing the content of sintering additives,the porosity of MoSi₂/Al₂O₃composites was controlled,and the excellent properties of MoSi₂/Al₂O₃composites were obtained when the content of MoSi₂/Al₂O₃composites was 8wt.%.?3?When the MoSi₂ content was 16wt.%,with the increase of sintering temperature,the flexural strength increased from 250 MPa to 279 MPa,and the fracture toughness increased from 5.23 MPa·m^1/2 to 7.73 MPa·m^1/2 at air atmosphere.However,the value of dielectric constant at 1450?is lower than it is at 1400?.When the sintering temperature was 1400?,the electrical conductivity reached a maximum value of 4.20 S·cm^-1,which contributed to the formation of a long electron transportation channel.