Comparative study on direct fluorination and surface properties of alumina-filled and unfilled epoxy insulators

In view of the significant performance improvement of unfilled epoxy insulators by direct fluorination, and the fact that all spacers in SF6 gas insulated systems are alumina-filled epoxy composites, to promote the application of the method for improving the performance of epoxy spacers, in this paper, alumina-filled epoxy (composite) and unfilled epoxy (pure) samples were prepared with the same formulation and process as those for epoxy spacers. The pure and composite epoxy samples were fluorinated under the same conditions, and comparative studies were performed on their surface physicochemical characteristics and properties. IR analysis and SEM imaging show no obvious influence of alumina particles on the fluorination of the epoxy matrix under the used fluorination conditions, while many nanoparticles and agglomerates appear on the surface and large microsized particles in the SEM imaging depth become less visible after the composite epoxy sample was fluorinated. Contact angle and electrical property measurements indicate that like the pure epoxy sample, surface hydrophilicity and surface conduction of the composite epoxy sample are also increased by the fluorination, while the increase in surface hydrophilicity or surface conduction is more significant or less significant, compared to the pure epoxy sample. All these are associated with the fluorination of the alumina particles and the interface change or reconstruction between the particles and the matrix.