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Polymers 2017, 9(10), 533; https://doi.org/10.3390/polym9100533

Dielectric and Carrier Transport Properties of Silicone Rubber Degraded by Gamma Irradiation

1
State Key Laboratory of Electrical Insulation and Power Equipment, Xi’an Jiaotong University, Xi’an 710049, Shaanxi, China
2
Research Institute for Materials Science and Technology, Waseda University, Shinjuku, Tokyo 169-8555, Japan
3
Department of Electrical Engineering and Bioscience, Waseda University, Shinjuku, Tokyo 169-8555, Japan
*
Author to whom correspondence should be addressed.
Received: 27 September 2017 / Revised: 16 October 2017 / Accepted: 19 October 2017 / Published: 20 October 2017
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Abstract

Silicone rubber (SiR) is used as an insulating material for cables installed in a nuclear power plant. Gamma rays irradiated SiR sheets for various periods at temperatures of 145 and 185 °C, and the resultant changes were analyzed by examining complex permittivity spectra and surface potential decay characteristics. Three different processes, namely, instantaneous polarization, electrode polarization due to the accumulation of ions to form double charge layers at dielectric/electrode interfaces, and DC conduction caused by directional hopping of ions, contribute to the complex permittivity. By fitting the spectra to theoretical equations, we can obtain the dielectric constant at high frequencies, concentration and diffusion coefficient of ions and DC conductivity for the pristine and degraded samples. The instantaneous polarization becomes active with an increase of dose and ageing temperature. The thermal expansion coefficient estimated from the temperature dependence of dielectric constant at high frequencies becomes smaller with an increase in dose, which is in good agreement with the experimental results of the swelling ratio. Additionally, trap distributions are calculated from surface potential decay measurements and analyzed to explain the variation in conductivity. Trap energy increases firstly, and then decreases with an increase in dose, leading to a similar change in DC conductivity. It is concluded that generations of both oxidative products and mobile ions, as well as the occurrence of chain scission and crosslinking are simultaneously induced by gamma rays. View Full-Text
Keywords: conductivity; dielectric property; gamma irradiation; SiR; trap distribution conductivity; dielectric property; gamma irradiation; SiR; trap distribution
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Min, D.; Yan, C.; Huang, Y.; Li, S.; Ohki, Y. Dielectric and Carrier Transport Properties of Silicone Rubber Degraded by Gamma Irradiation. Polymers 2017, 9, 533.

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