| In order to effectively improve the performance of epoxy composite materials,a variety of inorganic particles with high thermal conductivity and good electrical insulation have been applied to thermoset or thermoplastic polymers to improve the thermal conductivity and insulation performance of composite materials.In recent years,many researchers are keen to study the construction of an ordered network of fillers.At present,little research has been conducted on the influence of the magnetization treatment of silicon carbide particles on the breakdown,dielectric and thermal conductivity of epoxy composites.Therefore,the research is of great significance.Since silicon carbide has several crystal types,there are certain differences in the physical and chemical properties of different crystal types.In this paper,the most common α-SiC and β-SiC are selected for compounding with different proportions and different filling amounts,and the electrothermal performance of the prepared composite materials is tested.The results found that the breakdown strength of β-SiC is better than that of α-SiC,and that the dielectric constant and dielectric loss of β-SiC are lower than that of α-SiC,and the thermal conductivity of β-SiC is higher than that of α-SiC.When 30vol%β-SiC is filled,the thermal conductivity of the composite material reaches 0.9019W/(m·K),which is 48.58%higher than the α-SiC/epoxy composite filled with the same amount,360.15%higher than that of pure epoxy resin.According to the experimental results of the electrothermal performance of the composite materials prepared by the different crystal types,β-SiC with better comprehensive performance was selected for the next experiment.It is known that β-SiC itself has no paramagnetism and cannot be oriented under the action of an external magnetic field.Therefore,this article magnetized SiC particles and SiC whiskers,and added lye to the mixed solution of SiC particles,Fe2+ and Fe3+,and deposited ions on the surface of SiC through chemical reactions to form a layer of magnetic nano-Fe3O4.Then three ways of magnetization treatment were carried out,and the ordered composite material was successfully prepared.The study found that:"M-SiC/EP solid" composite material has better electrothermal performance than the original SiC/epoxy composite material.Compared with SiC/epoxy composites,the breakdown strength of M-SiC/epoxy composites with core-shell structure coated with Fe3O4 has a certain degree of improvement.Under the action of an external magnetic field,the magnetized SiC particles are oriented and arranged to construct an ordered network,which limits the movement and polarization of the epoxy resin macromolecular chain,so the "M-SiC/EP solid" composite material has a lower dielectric constant and dielectric loss.At the same time,the ordered network in the "M-SiC/EP solid" composite material also acts as a superior heat conduction path.The Fe3O4 coated SiC filler is arranged vertically under the action of an external magnetic field to build a particle-whisker pathway,which is consistent with the "M-SiC/EP solid" composite material.Compared with SiC/EP pre-composite,the magnetic field has a more significant effect on the orientation and chain formation of the magnetized particles inside the material.Therefore,the thermal conductivity of the composite material obtained by the magnetization treatment during curing is significantly improved.To sum up,this thesis studies the change law of the electrothermal properties of compound composites and ordered composites affected by filler crystal type,filling amount and orientation.It also realizes the selection of silicon carbide with better comprehensive performance and comprehensively improves the electrothermal performance of SiC/epoxy composites.These results indicate that the magnetization-oriented SiC-based polymer composites have broad application prospects in thermally conductive insulating materials for electrical equipment. |
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