Preparation Of Boron Nitride Nanosheets And Application In Thermal Management

With the high integration and high power of electrical and electronic equipment,the heat flux of electronic equipment is higher and higher.Thus,enhance of the thermal management capability of devices has become the key to promote the development of electronics industry.Thermal conductive nanofluids and thermal conductive composites play a vital role in nuclear power cooling,high voltage transport,aerospace and defense industries.In this research,boron nitride nanosheets(BNNS)were utilized as thermal conductive particles,Diw/BNNS nanofluids were prepared using water as the base fluid,and polydimethylsiloxane(PDMS)was composite with BNNS to prepare the BNNS/PDMS composites.The thermal conductivity of the Diw/BNNS nanofluid system and the BNNS/PDMS composite were investigated respectively.The BNNS aqueous dispersion was prepared by the molten alkali-assisted ultrasonication method.The Diw/BNNS nanofluid was obtained by concentrating the BNNS aqueous dispersion.By investigation of the thermal conductivity,viscosity and stability of Diw/BNNS nanofluid system,it was found that:(1)The compatibility of BNNS with water is improved due to-OH captured on BNNS surface,which was treated by molten alkali-sonicated;By concentration,the redispersion of nanoparticles can be avoided.Since,the BNNS can be dispersed more uniformly,and the Diw/BNNS nanofluid system is more stable.(2)The Diw/BNNS nanofluid system shows excellent thermal conductive performance.With the increase of BNNS,the thermal conductivity of the nanofluids significantly enhanced.When the BNNS content is 24 vol%,the thermal conductivity achieved 2.39 W m-1 K-1.The Diw/BNNS nanofluid system can be acted as an effective heat transfer medium to improve the heat dissipation of the equipment.Thermal conductive network was constructed in the PDMS matrix by combination of directional freeze-welding method.Through the investigation on the morphology and thermal conductivity of composites,it was found that:(1)Direct freezing-welding method can make full use of BNNS in-plane thermal conductivity to construct thermal conduction network and enhance heat dissipation;the "welding" effect of residual carbon enhances contact between adjacent BNNS.Further,reduces the phonons scattering in the interfaces and enhance the thermal conductivity of composite.When the BNNS content is 15.8 vol%,the thermal conductivity of the composite can reach 7.46 W m-1 K-1.(2)The residual carbon generated during vacuum high temperature treatment adheres on the surface of BNNS and forms extremely weak conductive network in the PDMS matrix.This weak conductive network gives BNNS/PDMS composites excellent antistatic properties.It can meet the requirements of some electronic equipment for antistatic properties of materials.