Comparative study on dynamic thermal-dielectric properties of epoxy composites with Al and Ni particles
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Dynamic thermal-dielectric behaviors of the aluminum (Al) and nickel (Ni)/epoxy composites were investigated by means of broadband dielectric spectroscopy measurements at the temperature of − 20 to 200 °C and in the frequency range of 1–107 Hz. Results indicate that the dielectric permittivity, loss and electric conductivity of the two composites increased with temperature and exhibited a clear abrupt rise around the glass transition temperature (Tg) due to the occurrence of α-relaxation relating to the mobility of epoxy chain segments. The transition behavior in electrical properties is almost identical for the two composites: insulator below Tg and semi-conductor above Tg. The large increase in dielectric permittivity, loss and conductivity with temperature above Tg can be ascribed to the formation of direct current conduction of thermal-activated charge carriers resulting from the matrix. Compared with Ni, the core–shell structured Al endows epoxy much lower dielectric loss and conductivity owing to the presence of nanoscale insulating alumina shell between Al core and matrix, which serves as an interlayer between the Al cores, and prevents them from direct contacting with each other, thereby leading to highly suppressed loss and conductivity.
The authors gratefully acknowledge the financial supports from the National Natural Science Foundation of China (51577154), the Key Laboratory of Engineering Dielectrics and Its Application, Ministry of Education, Harbin University of Science and Technology (KF20151111), Shaanxi Provincial Natural Science Foundation, China (No. 2016JM5014). And Wenying Zhou acknowledges the fellowship provided by the China Scholarship Council (CSC).
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