Preparation And Microwave Absorption Properties Of MAX Phase Powders

Because of the unique layered structure and excellent properties of both ceramic and metal,MAX phase materials show great application potential and research value in electromagnetic wave absorption field.It’s worth noting that how to efficiently and quickly prepare the MAX phase powders with high purity is the basis and key problem of the research and development of new MAX phase absorbing materials.In this paper,Ti₃Al C₂ and Ti₂Al N MAX phase powders with high purity were successfully prepared by microwave sintering method,and the preparation process,synthesis mechanism and variation rule of absorption properties were systematically studied.In addition,based on the controllable characteristics of MAX phase M/A atom layer elements,the MAX phase powders of M₂Al C（M=Cr,V,Ti,Mo）and Ti₃Al_xSi_1-xC₂（x=0.8,0.6,0.4）were designed and synthesized,and the absorption performance was improved and promoted.At the same time,an efficient and broadband Ti₃C₂T_x MXene absorbing material with 3D porous structure was prepared by etched Al atoms in Ti₃Al C₂ and alkalization induced flocculation.The main conclusions of this study are as follows:1.Ti₃Al C₂ powder with a purity of 97.5 wt.%can be successfully prepared by microwave sintering with 3Ti H₂/1.2Al/2C as raw material at 1300°C for 30 min.And using 1Ti H₂/1.15Al/1Ti N as raw material,Ti₂Al N powder with purity of 96.7wt.%was successfully prepared by microwave sintering at 1250°C for 30 min.Using Ti H₂ as titanium source in the synthesis process was more beneficial to improve the purity of Ti₃Al C₂and Ti₂Al N.The important factor is that the Ti H₂ was easy to dehydrogenate and decompose into form active Ti atoms at low temperature below the melting point of Al.And then the active Ti atoms easy to reaction with solid Al to the form titanium aluminum compounds,which reduced the intensity of MAX phase synthesis reaction.The Ti₃Al C₂ and Ti₂Al N MAX powders with lamellar structure have interference absorption characteristics to electromagnetic waves.For 75 wt.%Ti₃Al C₂/paraffin sample,the effective frequency range of the second-order interference absorption band was 7.8 GHz（10.2～18.0 GHz）in the thickness range of2.9～5.0 mm.With the thickness of 3.5 mm and the frequency of 14.8 GHz,the lowest reflection loss（RL（min））was-32.4d B and the effective absorption bandwidth（EAB）was 0.8 GHz（14.4-15.2 GHz）.For 75 wt.%Ti₂Al N/paraffin sample,the effective frequency range of the second-order interference absorption band was 7.9GHz（10.1～18.0 GHz）in the thickness range of 2.8～5.0 mm.With the thickness of5.0 mm and the frequency of 10.7 GHz,the lowest reflection loss（RL（min））was-20.4 d B and the effective absorption bandwidth（EAB）was 0.8 GHz（10.3～11.1GHz）.2.The Cr₂Al C,(Cr_1/2V_1/2)₂Al C,(Cr_1/3V_1/3Mo_1/3)₂Al C,(Cr_1/4V_1/4Mo_1/4Ti_1/4)₂Al C MAX phase powders can be successful obtained use the Cr,V,Mo,Ti,Al,C（graphite）powders as raw materials by microwave sintering at 1250°C for 30 min.The lattice parameters of M₂Al C increased with the atomic radius changed of Cr,V,Mo,and Ti.The obtained(Cr_1/4V_1/4Mo_1/4Ti_1/4)₂Al C still retains the 211 type layered MAX phase structure of Cr₂Al C and has good absorption performance of interference loss.The absorption performance of Cr₂Al C MAX phase can be improved effectively by doping V,Mo and Ti elements in M atom layer of Cr₂Al C MAX phase.For 80 wt.%(Cr_1/4V_1/4Mo_1/4Ti_1/4)₂Al C/paraffin sample,the effective frequency range of the first-order interference absorption band was 15.0 GHz（3.0～18.0 GHz）in the thickness range of 1.0～5.0 mm.With the thickness of 1.5 mm and the frequency of 11.4 GHz,the lowest reflection loss（RL（min））was-37.2 d B,and the effective absorption bandwidth（EAB）was 2.3 GHz（10.4～12.7 GHz）.It shows good absorbing performance and impedance matching characteristics.3.The Ti₃Al_xSi_1-xC₂MAX phase powders with different contents of Si element can be successful obtained use the Ti,Al,Si,C（graphite）powder as raw materials by microwave sintering at 1300°C for 30 min.The dielectric loss characteristics of Ti₃Al_xSi_1-xC₂MAX phase can be improved effectively by adding appropriate Si element into the A-position atom layer.With the content increased of Si,the Ti₃Al_xSi_1-xC₂MAX phase structure transforms from Ti₃Al C₂ to Ti₃Si C₂,and the lattice parameters decrease.The 75 wt.%Ti₃Al_0.6Si_0.4C₂/paraffin sample has good impedance matching and attenuation characteristics.The effective frequency range of the first-order interference absorption band was 14.9 GHz（3.1～18.0 GHz）in the thickness range of 1.0～5.0 mm.With the thickness of 2.5 mm and the frequency of7.0 GHz,the lowest reflection loss（RL（min））was-41.2 d B,and the corresponding effective absorption bandwidth（EAB）was 1.7 GHz（6.4～8.1 GHz）.Compared with the Ti₃Al C₂ MAX phase material,the absorption efficiency of Ti₃Al_0.6Si_0.4C₂ MAX phase material was improved obviously.4.A 3D porous Ti₃C₂T_x MXene material can be obtained quickly and effectively by adding proper amount of alkali（such as KOH,Na OH and Li OH）into the small layer Ti₃C₂T_x suspension.The alkali can induced the flocculation of Ti₃C₂T_x sheet into folds.The obtained Ti₃C₂T_x MXene material has a three-dimensional mesoporous and macroporous structure,a larger specific surface areas and a lot of active point sites.And the contents of-F and-Cl groups effectively reduced,and the contents of-O and=O groups increased.Meanwhile,the surface functional group structure was significantly improved.After annealing at 400°C for2h,the surface structure of Ti₃C₂T_x MXene was further optimized while the three-dimensional porous structure of the sample was not significantly damaged.The sample of K-A-Ti₃C₂T_x MXene which obtained by KOH alkalization and annealing at 400°C for 2h has a excellent absorption performance.For the 45 wt.%K-A-Ti₃C₂T_x/paraffin sample,the effective frequency range of the first-order interference absorption band was 15.4 GHz（2.6～18.0 GHz）in the thickness range of1.0～5.0 mm.With the thickness of 1.5 mm and the frequency of 12.6 GHz,the lowest reflection loss RL（min）is-42.8 d B,and the corresponding effective absorption bandwidth（EAB）was 2.7 GHz（11.4～14.1GHz）.Compared with Ti₃Al C₂MAX phase materials,the prepared three-dimensional porous Ti₃C₂T_x MXene material shows better electromagnetic wave absorption characteristics at room temperature.