Surface-Modificated Boron Nitride On Friction And Thermal Conductivity Performance

Hexagonal boron nitride nanosheets（BNNS）are advanced two-dimensional ceramic nanomaterials that can play an important role as fillers in composite materials in the field of friction and thermal conductivity.When BNNS is applied as friction additive in lubricants,the lack of lipophilic functional groups on its surface causes agglomeration or delamination when dissolved in lubricants,resulting in the inability of BNNS to function.When BNNS is applied to thermally conductive polymers as a thermally conductive filler,it is a major challenge to build good thermal pathways in thermally conductive polymers.All these greatly limit the practical application of BNNS.In this thesis,the main theme is to improve the performance of BNNS in two major areas of friction and thermal conductivity with surface modification of BNNS as an entry point.In the first part,lipophilic boron nitride nanosheets（BNNS）is prepared by alkylamine assisted ball milling method,and the effects of three different structures of alkylamines（octadecylamine ODA,tetradecylamine TDA,and trioctylamine TOA）as modifiers on improving the frictional properties of mineral base oils are investigated.The results show that the TOA-modified BNNS（BNNS-TOA）has the best dispersion stability in the mineral base oil.The friction coefficient of the mineral base oil with BNNS-TOA decreased by 20.2%,the wear width decreased by 75%,and the wear marks become significantly shallower.In addition,BNNS-TOA,which is well dispersed in mineral base oil,can build more thermal conductivity pathways,and its thermal conductivity is 8.83times higher than that of pure mineral base oil.In the second part,the hydrophilic BNNS is prepared by glycine-assisted ball milling to introduce carboxyl groups on its surface;The equally hydrophilic Al₂O₃ is introduced,and modified with the coupling agent KH550 to introduce amino groups on its surface;the hydrophilic BNNS and Al₂O₃provide the conditions for the occurrence of electrostatic self-assembly.The two thermally conductive fillers are self-assembled by vacuum-assisted filtration to form a thermally conductive filler（f-BNNS/f-Al₂O₃）with a three-dimensional structure.Finally,the effect of the ratio of f-BNNS and f-Al₂O₃ dosage on the thermal conductivity of the epoxy resin is investigated.When the mass ratio of f-BNNS to f-Al₂O₃ is 2:1,the thermal conductivity of the prepared f-BNNS/f-Al₂O₃ thermally conductive filler filled into the epoxy resin reaches 1.965 W m^-1 K^-1,which is 10.9 times higher than that of the pure epoxy resin.In summary,BNNS-TOA prepared in the first part of this work enhances the interaction with mineral base oil,has good dispersion stability in mineral base oil,and has significantly improved friction and thermal conductivity.The enhanced dual performance allows BNNS-TOA to better maintain the lubrication process as a friction additive.In the second part,f-BNNS/f-Al₂O₃ thermal conductive filler with three-dimensional structure is prepared,which can be filled into epoxy resin to effectively construct thermal conductivity pathways and form a good three-dimensional thermal conductivity network,greatly improving the thermal conductivity of epoxy resin.This has significant implications for the practical application of BNNS in the field of friction or thermal conductivity.