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In this article, silicone rubber (SiR) is filled with industry preferred micro-silica and specialty hexagonal boron nitride (h-BN) nanosheets, by varying the ratio between the two fillers, while keeping the filler to matrix ratio the same in all three composites. The fillers are added to SiR using an electrostatic disperser which aids in homogenizing the filler-polymer mixture by means of shearing force along with elongation. The performance of synthesized silicone composites are evaluated using thermal, erosion resistance, morphological, mechanical, and high-temperature dielectric properties. Addition of as low as 5 wt% h-BN fillers significantly improved the thermal properties; 6%–20% improvement in thermal conductivity and in less than half the weight loss compared to only silica filled composites with laser erosion. The morphological and mechanical analyses showed improved filler dispersion and filler to silicone matrix interaction owing to good filler dispersion achieved through the electrostatic dispersing method. The dielectric properties measured in wide frequency range, between 10−4 and 103 Hz and at elevated temperatures (up to 175 °C) showed a negligible effect of increase in h-BN content. Thus, this article implies that low amounts of h-BN in silica-silicone composites improve thermal conductivity and erosion resistance significantly and not altering the dielectric responses of these hybrid composites even at elevated temperatures. Hence these composites can find applications both in the high voltage industry and as electronic packaging materials. [ABSTRACT FROM AUTHOR]

This study introduces silicone elastomers with micro and nano-sized boron nitride (BN) and silicon carbide (SiC) particles with various doping levels to improve thermal properties and partial discharge resistance. The effect of micro and nano-fillers on thermal conductivity, coefficient of thermal expansion (CTE), and thermal stability are investigated. Polarization and depolarization current and partial discharge are measured to investigate the non-linear conductivity, trap energy density distribution, and partial discharge resistance. Experimental results show higher thermal conductivity, lower CTE, and better thermal stability than the original silicone elastomer. Large size fillers dominate the thermal conductivity when the doping level is low, whereas the composite microstructure plays a significant role in the thermal conductivity when the doping level is high. The combination of different filler type and size has less effect on thermal stability and CTE compared to the effect of the doping level. According to the depolarization current, the composite's trap depth is generally shallower than that of the original silicone elastomer. With increased doping level, the shallow trap density increases, providing hopping sites for carriers, whereas the deep trap density decreases, reducing the number of trapped charges. The partial discharge inception voltage is higher than that of the original silicone elastomer, and it increases with the doping level, which may be because the electrostatic field generated by diffused charges reduces the local electric field near the high voltage electrode. [ABSTRACT FROM AUTHOR]

To reduce the electric field distortion and increase the thermal conductivity of the dielectric materials in cable accessories, this paper proposes a method to prepare composites with good nonlinear electrical conductivity and high thermal conductivity. Silver nanoparticles grown on hexagonal boron nitride (AgNPs/BN) were prepared as a powder and introduced into ethylene propylene diene monomer (EPDM) to obtain AgNPs/BN/EPDM composites. The nonlinear electrical conductivity, thermal conductivity and breakdown field strength of the composites were investigated at different temperatures. The nonlinear electrical conductivity and thermal conductivity of the composites increased with increasing AgNPs content grown on BN. Moreover, the breakdown field strength decreased with increasing AgNPs, and exhibited a weaker temperature dependence than neat EPDM. Simulations showed that the composites could improve the electric field distribution in a cable accessory. [ABSTRACT FROM AUTHOR]

Transformer oil is widely used in electric transformers serving the dual functions as insulating medium and cooling material. However, safety and stability of power system is interrupted due to the operation failure of electric transformers in certain case. Therefore efforts should be focused on improving the property of transformer oil for the stable operation of insulating system. The purpose of this paper is to obtain a new type of nanomodified transformer oil with improved dielectric and thermal properties. Boron nitride (BN) nanoparticles with high thermal conductivity were dispersed into transformer oil to form the nanooil. Dielectric and thermal properties of the samples before and after modification were measured. Dielectric property experiments were performed in accordance with IEC standard. Discharge phenomenon in breakdown process was captured by a high speed CCD camera. In order to investigate the effect of BN nanoparticles on thermal property, temperature change and heat distribution of the samples in heat transfer process were measured by an infrared thermal imager and a temperature sensor. It is found that the nanooil has higher dielectric breakdown strength and lower dissipation factor which indicate better dielectric property compared with nonmodified oil. Obtained results show significant improvement in heat transfer process with increasing the concentration of BN nanoparticles. It is proposed that the nanoparticles create an interfacial region which contributes to the enhancement of dielectric strength. For thermal property the ballistic phonon transport of the nanoparticles acts as the key factor in the remarkable improvement. Furthermore, the improved thermal property of the nanooil has an inhibitory effect on the breakdown process according to the bubble theory. [ABSTRACT FROM AUTHOR]

This study investigated the effect of various ceramic micro and nano fillers on the different properties (dielectric and thermal) of a polyethylene (PE) matrix. The fillers used were alumina (Al2O3) and boron nitride (BN). The polymer composites were prepared by ball milling and thick films containing wt. 50% of the inorganic phase were pressed. The encapsulation of the inorganic additives into the PE matrix was successfully achieved. The real part of the dielectric permittivity of a microcomposite containing Al2O3 was found to be close to that of the PE matrix value whereas the losses remained quite low. Thermal conductivity of PE was greatly improved: it increased by about 50% irrespective of the nature and size of the fillers. When the filler was nano BN, the breakdown strength was found to be slightly reduced by only 5%. This could be due to the size of the particles or to the high percentage of additives and the interface behavior of the fillers/matrix. Improvement of the PE surface resistance to discharges was achieved, specially with using nano-BN. [ABSTRACT FROM AUTHOR]