292 / 2022-03-15 08:40:03

Overall Improvements in Outdoor Performance of ATH-free Silicone Rubbers by Direct Fluorination

silicone rubber, direct fluorination, outdoor performance, performance improvement

Because of many desirable properties, particularly the unique hydrophobic recovery, silicone rubbers (SIRs) are widely used in high voltage outdoor insulation. However, SIRs in service will be aged or degraded and their outdoor performance will deteriorate due to the electrical, environmental and mechanical stresses, so that the pollution flashover for high-voltage outdoor insulators may occur especially in the later service. In this report, to improve the outdoor performance, SIRs were directly fluorinated using the F₂/N₂ mixture. The improvements in the outdoor performance by direct fluorination are summarized, which contain the following aspects. Direct fluorination always leads to a significant increase in surface hydrophobicity, as long as the SIR contains silicone oil in the bulk. Direct fluorination can obviously improve the moisture barrier properties of SIR with an association of the barrier properties with fluorination condition or physicochemical characteristics of the fluorinated layer. Depending on the type, formulation and fluorination conditions of SIR, direct fluorination can increase its surface conductivity by one to four orders of magnitude, and thus suppress surface charge accumulation. Direct fluorination can always greatly improve the dc flashover performance of SIR, and depending on its formulation and fluorination conditions, the dc flashover voltage is increased by 30 ~ 60%. Direct fluorination can also significantly improve the resistance of SIR to corona or arc discharge, and enhance the ac flashover performance to some extent. Another surprise is that such a thin fluorinated surface layer, with micron thickness, can significantly improve the tracking and erosion resistance of SIR. The improvements in the outdoor performance are attributed to the changes in composition and structure of the SIR surface layer. Both the organic matrix and inorganic particles in the surface layer are fluorinated, and the fluorination of the matrix is not only the substitution of fluorine for hydrogen in methyl groups, but many methyl groups are directly replaced by hydrogen atoms. The results have important potential applications for improving the outdoor performance of high voltage insulators.