Etching and the Morphology of Cross-Linked Polyethylene Cable Insulation

The techniques of etching by carbon tetrachloride vapor and by permanganic acid are shown to be prone to artifacts, and so earlier conclusions based on these techniques, i.e. that XLPE cable insulation has a large scale (>> 10 µm) spherulitic texture structure, need to be reexamined. A comparison with XLPE film samples, where spherulite size is readily determinable by small-angle light scattering and optical microscopy, indicates that typical spherulite dimensions are <5 µm. Examination of freeze-fractured surfaces through XLPE insulation containing water-trees revealed cavities up to 10 pm diameter with no evidence of interconnecting channels. Freeze-fractured surfaces through electrical trees revealed channels several micrometers in diameter with evidence of extensive melting and polymer degradation.