Preparation And Properties Of 3D LAS/CNT Composites By Direct Writing 3D Printing

Lithium aluminosilicate（Li₂O-Al₂O₃-SiO₂,LAS）ceramics are widely used in shielding materials for precision instruments because of their low coefficient of thermal expansion,high mechanical strength,and low dielectric constant.The development of LAS ceramics is limited by their brittleness,which makes it difficult to process three-dimensional interconnected porous structural materials.In order to prepare complex structural parts,this study used the direct ink writing（DIW）technique to prepare inks with excellent printing performance and high solid phase content and to promote near-net molding of the print.The purpose of this paper is to provide insight into the DIW molding process and performance of LAS ceramic inks,specifically with respect to the design of heat-treated powders,addition of dispersants,sintering temperature,and how they affect the object composition,microstructure,and performance of printed samples.In addition,chemical vapor deposition was used to grow carbon nanotubes（CNT）on the 3D lattice structure,to analyze the condition of CNT growth on the surface of 3D lattice structure ceramics with ferrocene and nickel nitrate hexahydrate as catalysts,and to analyze the wave absorption performance and mechanism of the 3D lattice structure LAS/CNT composites.In this study,the LAS precursor powder prepared by sol-gel method was calcined,and it was concluded that the glass powder after 1000℃treatment had a low viscosity.When propylene glycol methyl ether acetate（PEMEA）and hydroxyethyl cellulose（HEC）were added at 0.5 wt.%with good dispersion and stability,the configured printing paste showed shear thinning effect with increasing shear rate.When the LAS glass powder was added at72 wt.%,the configured slurry was obtained with a good yield stress value of 235.2 Pa and a flow index of 0.348,which had good rheological properties and was favorable for printing and molding.In this study,the LAS precursor powder prepared by sol-gel method was calcined at500-1000℃,and the viscosity of the powder decreased from 4886 m Pa·s at the beginning to 625 m Pa·s with the increase of calcination temperature,and the viscosity decreased by87%.When propylene glycol methyl ether acetate and hydroxyethyl cellulose added to 0.5wt.%has good dispersion and stability and low viscosity,the configuration of the printing ink with the increase in shear rate,the ink shows shear thinning effect.It has a good yield stress value of 235.2 Pa when the solid phase content is 72 wt.%,and the flow index reaches0.348,which has good rheological properties and is favorable for printing and molding.Sintering of LAS blanks at 1000-1350°C revealed that the diffraction peaks of LAS enhanced with increasing sintering temperature,and the flexural strength of LAS ceramics sintered at 1000°C was 31.86±3.16 MPa,the compressive strength was 40.02±3.43 MPa,the average linear shrinkage was 0.14%,and the porosity was 16.85%.Sintering at 1300℃yielded a flexural strength of 46.40±3.01 MPa and a compressive strength of 65.96±5.28MPa,an average linear shrinkage of 0.84%,and a low porosity of 0.29%,yielding a 45.63%improvement in flexural and 64.81%improvement in compressive properties.The flexural strength of the sintered LAS ceramics at 1350°C was 43.22±2.95 MPa and the compressive strength was 54.70±3.24 MPa.The mechanical properties were degraded due to microcracking at this temperature of sintering.The coefficient of thermal expansion decreases with increasing sintering temperature and is as low as 0.19×10^-6·K^-1 at 1350°C.Three-dimensional lattice glass-ceramics were prepared by in situ growth of carbon nanotubes by chemical vapor deposition to obtain three-dimensional lattice structured LAS/CNT composites.It was shown that the surface growth of the 3D lattice structure obtained by using ferrocene as the catalyst precursor was not uniform and the CNT diameter was shorter;the surface growth of the 3D lattice structure obtained by using the catalyst precursor nickel nitrate hexahydrate was more uniform and the CNT diameter was finer,and when calcination was carried out at different temperatures,it could be concluded that the CNT diameter was finer and longer as the calcination temperature increased.The analysis of the 3D lattice composites made with different catalyst concentrations showed that the CNT content increased with the increase of catalyst concentration,and the increase was slow after the catalyst concentration reached 10 wt.%.It was concluded from the analysis that when the catalyst precursor content was 10 wt.%,the CNT in the specimen had the most defects and the lowest graphitization and orderliness.By analyzing the dielectric loss,magnetic loss,reflection loss and impedance matching of the 3D grating composite,it is concluded that the sample has the minimum RL_min value of-51.5 d B when the CNT content is 6.56 wt.%,and the EAB can reach 3.7 GHz at 4 mm thickness with 88.09%coverage in X-band and has the maximum attenuation constant,good impedance matching value and Excellent absorption performance.