Leakage current analysis and infrared spectroscopy of outdoor insulating materials aged in a salt-fog test

A 1000 h salt-fog test using low salinity with resting periods between the salt-fog cycles was employed for the comparison and ranking of a series of silicone rubber and EPDM rubber materials. In addition, these materials have been analysed by Attenuated Total Reflection-Infrared (ATR-IR) spectroscopy, in order to determine the degree of surface oxidation. The electrical analyses involved the measurements of high-frequency and low-frequency leakage current components during the actual salt-fog tests. The leakage current measurement enabled a rough ranking of the materials essentially into two groups whereas ATR-IR spectroscopy provided data which more sensitively ranked the different materials. It was shown that samples with a higher degree of surface oxidation also during the salt-fog test exhibited higher leakage currents. In another test series involving only silicone rubber materials modified with different silicone oils, differences in the salt-fog test results were small. However, the samples with the highest leakage current exhibited a diminished alumina trihydrate content at the surface which apparently protected the rubber from oxidation