Preparation Of Three-dimensional Boron Nitride Composites And Research On Its Thermal Conductivity

With the continuous progress of modern society and the continuous development of science and technology,electronic products are playing an increasingly important role in people’s daily lives.At present,electronic products are developing in the direction of miniaturization,high sensitivity and multi-functionality.The power of the device has also been greatly improved,and the heat inside the device has also continued to accumulate.A good heat dissipation effect can greatly increase the service life of the battery.Because of this,it has become more and more important to improve the thermal conductivity of the polymer.Currently,there are two main methods,one is to synthesize composite materials with high thermal conductivity,and the other is to fill polymers with inorganic fillers with high thermal conductivity.In recent years,two-dimensional（2D）structural materials such as hexagonalboron nitride（h-BN,hereinafter referred to as BN）have received increasing attention due to their high chemical stability,excellent thermal conductivity,and excellent electrical insulation,especially considering their wide range of availability,low price,and high thermal conductivity.However,high thermal conductivity often requires extremely high filler loadings in composites,which can lead to high cost,high weight,and greatly reduce mechanical properties.This is mainly because it is difficult to form good thermal conduction paths in the polymer matrix when the filler loading is low.In this paper,a simple and economical template method is proposed to obtain three-dimensional boron nitride nanosheets（3D BNNS）by using polyurethane foam（PU）as a template and finally removing the template by pyrolysis to construct phonon transport channels and reduce the thermal resistance between the boron nitride filler and the thermally conductive matrix.The 3D BNNS composite with epoxy resin shows good thermal conductivity.When the packing load is 20 wt%,the thermal conductivity is 1.25W m^-1 K^-1.Based on this,in order to improve its poor longitudinal thermal conductivity for the anisotropy of BNNS,we used fluidized bed chemical vapor deposition（FB-CVD）to in-situ grow carbon nanotubes（CNTs）on the surface of BNNS.The BNNS/CNTs filler was obtained,the CNTs acted as a"bridge"between BNNS and its thermal conductivity was tested.The results showed that the thermal conductivity of 3D BNNS/CNTs_15%/Epoxy reached 1.49 W m^-1 K^-1 when the filler loading is 20 wt%.The3D BNNS/CNTs_15%/Epoxy composite provides 60%higher thermal conductivity co MPared to BNNS/Epoxy for the same amount of loading,co MPared with pure epoxy resin,the thermal conductivity is increased by 1046%,and offers remarkable electrical insulation with electrical resistivity over 10¹⁰Ωm.In addition to the template method,this article also introduces a method for preparing three-dimensional composites through a simple self-assembly process.After the test,the thermal conductivity of the final 3D epoxy composite material reached 1.61 W m^-1 K^-1.In conclusion,the three-dimensional structure boron nitride composite prepared in this study can form effective phonon transmission channels and thermal conductivity networks inside the material,greatly improving the thermal conductivity.The BNNS/CNTs packing was obtained by FB-CVD,and the carbon nanotubes acted as a bridge between the BNNS,which effectively prevented phonon scattering.At the same time,the obtained material also has excellent insulating properties and mechanical properties,which can effectively prevent the short circuit of electronic devices,and has a broad application prospect in the field of microelectronics.