Electrical and Environmental Aging of Silicone Rubber

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This is a laboratory study on the aging of SIR and hydrophobicity recovery. UV radiation, corona discharges, acid rain, dry-band arcing are employed as sources of the aging. Chemical and morphological analysis is used to detect the surface chemical and structural changes derived from these stresses. The nature of highly mobile low molecular weight (LMW) chains achieving a quick recovery of the hydrophobicity is carefully examined. Their generation and extinction caused by these stresses are investigated.It is found that hydrophobic transfers of SIR resulting from electrical and environmental stresses are investigated as a clue to draw their aging scenarios and estimate their lifetimes. Roles of UV radiation, corona discharges and dry-band arcing during the aging is clearly identified. It is shown that oxidation that induces crosslinking, branching, interchanging in PDMS are the most dominant chemical reactions. Furthermore, highly mobile LMW chains (cyclic silicone oligomers of 4 to 6 … More molecular units) play a significant role to regain the hydrophobicity temporarily lost by electrical and environmental stresses. However, with the development of oxidation, silanol groups are formed, which are byproducts of oxidation, and they prevent highly mobile LMVV chains from migrating onto hydrophilic layers. Moreover, highly mobile LMW chains decrease due to crosslinking and their evaporation. When the recovery of SIR worsens, the above chemical reactions should take place. Hence, the atomic presence of oxygen at the surface can be a helpful indication to determine the aging level of SIR.However, in this case, ESCA able to analyze very shallow layer of material surfaces (<10 nm) would not be useful because mobile LMW chains hide the aged surfaces. EDX with high accelerating voltage to penetrate deeply into the sample (mere than 1 μm) would be convenient. The amount of cyclic silicone oligomers in the rubber is also significant information to predict the lifetimes. From all the information regarding their aging up to now, this study could draw a typical scenario of all lives of SIR used for outdoor HV insulation. This scenario proposed will be verified by the future test results of field aging. Less