The increasingly developed microelectronic devices have put forward higher requirements on thermal conductive and electrical insulating thermal interface materials, and the silicone rubber composites with high thermal conductivity and electrical insulating can be prepared through construction of micro-nano hybrid heat conduction network. First, a nano-alumina coated graphene oxide was prepared by a simple and green self-assembly strategy, and it was reduced into TRGO@Al₂O₃ nano-hybrid filler by high temperature treatment. Then it was mixed with micron alumina and filled into liquid silicone rubber. The influence of different nano alumina coated amounts on the thermal conductivity and volume resistance of the system was studied by adjusting the ratio of nano alumina to graphene oxide. The synergistic thermal conductive effect of the micro-nano hybrid system was studied by controlling the ratio of nano-hybrid filler to micron alumina. The results show that when the 3% of TRGO@Al₂O₃ and 54% of micron alumina are compounded, the thermal conductivity of the composite reaches about 2.5 W/(m·K), and the volume resistance is greater than or equal to 10⁹ Ω·cm.

To investigate the key factors of design for thermo-expandable sheets, we made thermo-expandable sheets from two types of glass mat with different fiber diameter and PA thermoplastic film. Different thermo-expandable sheets were prepared by changing the fiber diameter, resin content and density, and their thermal expansion rate and effect were studied. The results show that the thermal expansion effect of thermo-expandable sheets is codetermined by the elastic potential energy of fiber and the viscous resistance of melting resin. Under the same composition and density condition, the thermal expansion rate of thermo-expandable sheets increases with the increase of fiber diameter. There is a critical resin content for thermo-expandable sheets. When the resin content is below the critical value, the thermal expansion rate increases with the increases of resin content. When the resin content is above the critical value, the thermal expansion rate decreases with the increase of resin content. The critical resin content decreases with the increase of fiber diameter. When the single fiber diameter and resin content is unchanged, the higher the density of thermo-expandable sheets, the greater the thermal expansion rate.

In order to improve the thermal conductivity and environmental resistance of motor insulation system, we analyzed the conventional properties, heat resistance, thermal conductivity, and environmental resistance of a high thermal conductive and high temperature resistant epoxy encapsulating resin. A prototype was made, and the application performance of the epoxy encapsulating resin in low voltage motor was tested. The results show that the epoxy encapsulating resin has excellent mechanical and electrical properties, excellent low temperature and thermal shock resistance, and good compatibility with enameled wire, and the thermal conductivity and temperature index reach 1.18 W/(m·K) and 187.5℃, respectively. The application of high thermal conductive insulating resin could effectively improve the thermal conductivity of the motor insulation system, under the same conditions, the temperature rise of motor decreases by 20.7℃ compared to the motor with ordinary high temperature resistant insulating varnish. At the same time, compared with the vacuum pressure impregnation process, the insulation system of the motor made by the vacuum encapsulation process has better integrity, electrical properties, and humidity resistance, and the disadvantage of low paint hanging at the groove is avoided.

Polymer materials such as epoxy resin have hidden dangers of thermal failure and insulation failure during long-term service since its low thermal conductivity. In this study, a high thermal conductive composite insulating material was prepared by filling micron boron nitride and nano alumina with high thermal conductivity and high insulation properties to epoxy resin, and the effect of filling amount and ratio of fillers on the thermal conductivity and insulation properties of composite materials were studied. The results show that when the total filling content is 30% and the mass ratio of micron boron nitride to nano alumina is 3∶1, the thermal conductivity, breakdown time, and imaginary part of complex permittivity (ε″) of the composite materials is 1.182 0 W/(m·K), 31.9 s, and 0.034, respectively, which is improved by 697%, 21.7%, and 406% compared with epoxy resin, respectively. The composite material has good resistance performance under high frequency and high electric field.

The thermal conductivity of insulating varnish could be improved by adding inorganic oxide thermal conductive material into the epoxy modified unsaturated polyester resin. The effect of particle size and surface modification of fillers on the sedimentation of insulating varnish and effect of different filler content on the thermal conductivity and viscosity of insulating varnish were studied. A high thermal conductive and solvent-free insulating varnish was prepared, and its performance was characterized. The results show that the surface modification of filler could reduce its sedimentation rate. When the filler content is 40%, the viscosity of insulating varnish is 72 s, the thermal conductivity reaches 0.46 W/(m·K), and the insulating varnish exhibit no sedimentation at 40℃ after 6 days, which indicates that it has practical application value.

A polyacrylonitrile (PAN)/styrene-isoprene-styrene (SIS) composite fiber membrane was prepared by electrospinning method. The effects of different PAN/SIS ratios on its porosity, liquid absorption, thermal stability, mechanical properties were studied. The results show that when the ratio of PAN to SIS is 8∶2, the SIS/PAN composite membrane fiber prepared has the most cross-linked structures, uniform size, and the best mechanical properties. The tensile strength is 20.29 MPa, the porosity and absorption rate reach 47.8% and 310.7%, respectively, and the ionic conductivity is 2.03×10^-4 mS/cm. Under the condition of 0.2 C multiplier, the initial discharge specific capacity of Li-ion battery assembled by the composite fiber membrane is 146.4 mAh/g, the discharge specific capacity fluctuates little after 50 cycles, and the capacity retention rate is as high as 98.02%, showing good cycle stability.

A silicon carbide/organic montmorillonite/epoxy resin micro-nano non-linear corona resistant composite material was prepared. The influence of silicon carbide and organic montmorillonite content on the dielectric properties of the corona resistant material was studied. Bars were prepared using the corona resistant material, and their corona resistance and surface temperature were tested. The results show that the addition of a certain amount of nano organic montmorillonite could effectively improve the non-linear characteristic of the corona resistant composite, reduce the surface temperature of anti-corona area, and improve the corona resistance of bars.

Two kinds of modified magnesium hydroxide (MH) were used as flame retardant, and then compounded with low density polyethylene (LDPE) to prepare LDPE/MH flame retardant materials. The effects of the flame retardants on the mechanical properties, flame retardant properties, thermal stability, and electrical properties of the materials were studied. The results show that the flame retardant properties of the materials increase significantly after adding the modified magnesium hydroxide flame retardant, but the mechanical properties, thermal stability, and electrical properties decrease. The flame retardant of the LDPE with amino silane coupling agent modified magnesium hydroxide is better than that of the LDPE with alkyl silane coupling agent modified magnesium hydroxide, but its adverse effects on mechanical properties and electrical properties of materials are more obvious. When the addition amount of alkyl silane coupling agent modified magnesium hydroxide is 70 phr, the comprehensive properties of the material are better.

Considering the heat transfer and charge accumulation process in DC GIL comprehensively, we established an electro-thermal multi-physics field coupling model of DC GIL. On the basis of this model, the effect of the volume conductivity of insulating materials on the surface charge accumulation of basin type insulator was simulated and calculated under the coupling action of DC electric stress and thermal stress. The results show that the surface charge accumulation of insulator can be inhibited effectively by decreasing the volume conductivity of typical insulating materials for current AC basin type insulator by two orders of magnitude. However, if the volume conductivity of insulating materials decreases excessively, the surface charge accumulation of basin insulator will be aggravated.

The effects of electric field and temperature on the diffusion behavior of water molecules in nano-SiO₂ modified insulating oil were studied by molecular simulation technology. The results show that the water molecules are polarized under electric field, and the water molecules would change from an original disordered arrangement to an ordered arrangement along the direction of electric field. Therefore, under the action of electric field, the Brownian motion of water molecules weakens, and the diffusion ability of water molecules in oil decreases. The electrostatic force between water molecules and oil medium was enhanced by electric field, which is 2‒3 times bigger than that without electric field. This is also the main reason for the increase of interaction energy between water molecules and oil medium under electric field. In addition, under the action of electric field, the free volume fraction of the model decreases, and the effect of temperature on the hydrogen bond between O and H atoms in the model weakens.