Experimental investigation of the degradation mechanism of silicone rubber exposed to heat and gamma rays

et al. 2019

Self Cite

For conducting comparative research, samples of cross-linked polyethylene (XLPE), made exactly in the same manner as those used in nuclear power plants, were aged in two ways: purely thermally, and concurrently with heat and γ -irradiation, for long periods up to 2000 h. They were then examined by an indenter, mid-infrared absorption spectroscopy, broadband dielectric spectroscopy, and measuring the electrical conductivity. As a result, it became clear that the effect of radiation is more dominant than that of heat on the oxidation or carbonyl formation in XLPE. However, heat is a more determining factor on the surface hardness of XLPE. In addition, the complex permittivity of XLPE increases as a result of the appearance of abundant carbonyl groups. Both the carbonyl index and indenter modulus can be indicators of aging.

Section: Resultsmentioning

confidence: 99%

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

Liu

Miyazaki

et al. 2019

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“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Yamaguchi

Ishii

et al. 2020

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Thermal degradation was performed at 175, 200, and 250 °C from 100 to 2000 h on flame‐retardant ethylene propylene rubber (FR‐EPR) with the same compositions as those used in the insulation of a safety‐related cable in nuclear power plants. For these samples, indenter modulus (IM), elongation at break, tensile strength, and complex permittivity were measured to clarify mechanical and dielectric properties. Fourier transform infrared absorption and differential scanning calorimetric spectra were also measured to determine structural changes. As a result, it was found that FR‐EPR becomes hard by oxidation and crosslinking, and that it becomes brittle as the degradation becomes more severe. In addition, such changes in mechanical properties by the aging occur much earlier than the changes in dielectric properties. Regarding this, IM is a good indicator to examine the degradation degree of FR‐EPR. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

“…(b) that

ϵ_{normalr}^{″}

shows another decreasing trend with increase in the aging period. According to our previous study, cross‐linking is the main thermal aging mechanism of SiR . Carrier transport becomes difficult when SiR is strongly cross‐linked, which explains the above declining trend in

ϵ_{normalr}^{″}

.…”

Section: Resultsmentioning

confidence: 91%

Numerical evaluation of complex permittivity of silicone rubber based on Jonscher's law

Yang

Ito

et al. 2020

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In this work, the two parts of complex permittivity in the frequency range 1–104 Hz were measured for sheet‐shaped samples of silicone rubber under various aging conditions. After that, fitting equations based on Jonscher's law were used to evaluate both the parts. As a result, it is clearly indicated that the fitting parameters in the equation of ϵnormalr″ are linearly correlated with those in the equation of ϵnormalr″. This indicates that common information is contained in both ϵnormalr′ and ϵnormalr″. A possible mechanism is also proposed to explain this phenomenon. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.