RESUMEN
Composite insulators have excellent performance and are more and more widely used in power grid. The performance of composite insulators with different service duration will decline in varying degrees, which could pose a threat to the safe operation of power grid. In order to investigate the influence of service duration and electric field strength on insulator shed performance, the sheds at different positions of insulators with different service duration are sampled. The hydrophobicity, material and mechanical properties of the samples are tested, and then the micro material properties tests are performed in terms of SEM, FTIR and XPS tests. Based on the above test results, the aging law and its mechanism of silicone rubber sheds are analyzed. The results reveal that the performance of insulator shed gradually decline with the increase of service life. The hydrophobicity and hardness of high-voltage end insulator are similar to that of middle section insulator, while other parameters are obviously different, indicating that the electric field can aggravate the aging. FTIR results show that the main chain and hydrophobic side chain of silicone rubber are destroyed, and the oxygen-containing groups increased, indicating that thermal oxygen aging occurred during operation. XPS and SEM results show that the crosslinking degree of silicone rubber increases and the porosity increases. The above changes in the microstructure of silicone rubber lead to the decline of insulator performance.
RESUMEN
The stability of the thermal properties of diamond/Al composites during thermal cycling is crucial to their thermal management applications. In this study, we realize a well-bonded interface in diamond/Al composites by interfacial in situ Al4C3 engineering. As a result, the excellent stability of thermal conductivity in the diamond/Al composites is presented after 200 thermal cycles from 218 to 423 K. The thermal conductivity is decreased by only 2-5%, mainly in the first 50-100 thermal cycles. The reduction of thermal conductivity is ascribed to the residual plastic strain in the Al matrix after thermal cycling. Significantly, the 272 µm-diamond/Al composite maintains a thermal conductivity over 700 W m-1 K-1 after 200 thermal cycles, much higher than the reported values. The discrete in situ Al4C3 phase strengthens the diamond/Al interface and reduces the thermal stress during thermal cycling, which is responsible for the high thermal conductivity stability in the composites. The diamond/Al composites show a promising prospect for electronic packaging applications.
RESUMEN
Manipulating the interfacial structure is vital to enhancing the interfacial thermal conductance (G) in Cu/diamond composites for promising thermal management applications. An interconnected interlayer is frequently observed in Cu/diamond composites; however, the G between Cu and diamond with an interconnected interlayer has not been addressed so far and thus is attracting extensive attention in the field. In this study, we designed three kinds of interlayers between a Cu film and a diamond substrate by magnetron sputtering coupled with heat treatment, including a W interlayer, an interconnected W-W2C interlayer, and a W2C interlayer, to comparatively elucidate the relationship between the interfacial structure and the interfacial thermal conductance. For the first time, we experimentally measured the G between Cu and diamond with an interconnected interlayer by a time-domain thermoreflectance technique. The Cu/W-W2C/diamond structure exhibits an intermediate G value of 25.8 MW/m2 K, higher than the 19.9 MW/m2 K value for the Cu/W2C/diamond structure and lower than the 29.4 MW/m2 K value for the Cu/W/diamond structure. The molecular dynamics simulations show that the G of the individual W2C/diamond interface is much higher than those of the individual Cu/diamond and W/diamond interfaces and W2C could reduce the vibrational mismatch between Cu and diamond; however, the G of the Cu/W2C/diamond structure is reduced by the lower thermal conductivity of W2C. This study provides insights into the relationship between the interconnected interfacial structure and the G between Cu and diamond and offers guidance for interface design to improve the thermal conductivity in Cu/diamond composites.