Surface characterization analysis of silicone rubber after long term corona and humidity exposure

The effect of corona discharge is unavoidable during the operation of a composite insulators umbrella skirt made of silicone rubber. The aging of this material is one of the main problems facing composite insulators. In this paper, two kinds of silicone rubber housing materials (HTV and LSR) are used as samples. A multi needle plate electrode is used to simulate corona discharge, and a glass desiccator is used to simulate the environment of high humidity (>90%). The effects of long term corona and humidity exposure were evaluated by means of different standard surface characterization techniques, such as XPS, SEM and AFM. Test result show that surface oxidation for the exposed specimens was revealed by the XPS analysis. Cracks with the width about 1–8 μη and thickness about 0.3–1.5 μη were found on the surface through SEM analysis. The low molar mass siloxanes diffused to the surface through the cracked silica-like layer which reduce the free surface energy and lead to the recovery of hydrophobicity. The AFM analysis revealed the roughness of the significantly reduced after the exposure.