Three dimensional imaging of electrical trees in micro and nano-filled epoxy resin

The authors have previously shown that electrical trees in unfilled polymers can be three-dimensionally (3D) imaged using X-ray computed tomography (XCT) or serial block-face scanning electron microscopy (SBFSEM). Here, we present the results of 3D imaging and analysis of electrical trees in filled epoxy systems for the first time. Electrical trees created in unfilled, micro silica-filled and nano silica-filled epoxy resin were scanned using XCT at the Diamond Light Source synchrotron and then also imaged using SBFSEM. 3D virtual replicas of the trees have been generated and their structures characterised. Imaging in micro-filled epoxy is more challenging than in nano-filled epoxy. It was found that trees in samples filled up to 20 wt% with micro silica can be imaged using either XCT or SBFSEM. In the case considered, the mean diameter of tree channels in micro-filled epoxy was found to be considerably smaller (0.6 mu m) than in unfilled or nano-filled epoxies (3 mu m).