Study on the effects of long term corona and humidity exposure of silicone ruber

The knowledge of the resistance of silicone house materials to long term corona and humidity exposure is very important for standardizing test methods and minimum requirements for properties of this material. Two types of silicone rubber were used in this paper. A long term (10 weeks) corona and humidity exposure was conducted in a glass desiccator with a dry air flow at rate 5 L/min (for corona exposure) and high humidity condition (RH>90% for humidity exposure). For defining the treatment condition, the corona discharge current, the power release from the electrode and the ozone concentration during the treatment were measured. The results show that the treatment yielded a strong reduction of surface resistivity of both the materials, though still remaining within the limits set for safe functioning in outdoor applications. At the same time the mechanical properties were not affected significantly, less for the HTV material. At the same time, the hydrophobic properties, after an initial decrease, recovered with the duration of the treatment. These changes could be coupled to the formation and fracturing of oxidized and brittle silica-like surface layers. The latter was more intensive on the LSR material.