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

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.

Comparison of the effects of heat and gamma irradiation on the degradation of cross‐linked polyethylene

“…However, those aged at 155 °C show a distinct further increase in conductivity when the aging period was 800 h, although the conductivity then decreases slightly when the aging is continued for very long periods such as 1200, 1600, and 2000 h. When the XLPE sample is aged under these extreme conditions, its molecular structure is broken severely as mentioned above and the sample becomes brittle. This would hinder the transport of charge carriers .…”

Degradation of Mechanical and Dielectric Properties of Flame‐Retardant Ethylene Propylene Rubber by Thermal Aging

“…We have conducted extensive research for clarifying the degradation behavior and mechanisms of insulating polymers important for NPPs such as silicone rubber, XLPE, FR-XLPE [1][2][3][4][5][6][7][8][9][10], and FR-EPR. However, as for FR-EPR, we have not made an extensive report in a peer-reviewed journal.…”

Development of Magnetic Compound Fluid Rubber Sensor for Practical Usage on γ-Irradiation and Energy Harvesting for Broad-Band Electromagnetic Waves

“…However, the degradation of the rubber is a serious problem in that the rubber becomes hard. This has been reported in investigations on silicone rubber [20] and NR [21] as well as the results of the mechanical properties of various kinds of rubber irradiated by γ-rays [22] [25]. Therefore, in the present report, we investigate the effect of γ-rays on the mechanical properties of an MCF rubber sensor under compression and tension.…”