The Research on Corona Aging Silicone Rubber Materials’ NMR Characteristics

Nuclear Magnetic Resonance (NMR) detection is a non-destructive testing method that can be used to detect the aging state of organic materials. A unilateral NMR sensor is used in this study to detect the aging state of the corona aging samples of silicone rubber materials after 100-hour's corona aging under different humidity. At the same time, a comparative analysis is made between the NMR results and the conventional methods results such as Fourier Transform Infrared Spectroscopy (FTIR) and static contact angle test. The results show that with the effect of corona discharge, the polymer structure of the silicone rubber materials change to a certain extent. These changes are shown as the effective transverse relaxation time $T_{\mathrm {2eff}}$ of aged sample decreases in the NMR detection. The results of NMR and FTIR both show that the molecular crosslinking density of silicon rubber materials increases, and the activity of the H-containing group decreases. With the increase of relative ambient humidity, $\Delta T_{\mathrm {2eff}}$ gradually increase, and it means the corona aging state is becoming much severer. The results of NMR are consistent with the results of FTIR and contact angle tests. The $T_{\mathrm {2eff}}$ of the same sample tested at different time does not have significantly changes. This indicates that the NMR characteristic of silicon rubber materials after corona are irreversible. The NMR method can test the permanent damage of silicon rubber materials caused by corona. Compared with the static contact angle test, the NMR method can analyze silicon rubber materials from the molecular structure level, and it has good portability and orientation. Meantime, NMR method can achieve a non-destructive aging state detection. Hence the NMR method will provide reference for the operation and maintenance of the silicone rubber composite insulator.