The research on microstructure of water trees in polyethylene

So far, there is no general agreement on the microstructure of water trees, and two models have been proposed. In one model, it is considered that a water tree consists of continuous paths such as microchannels, while in the other model it is taken into account that a water tree is composed of a number of microcavities which are not connected. In this paper, AgNO₃ (silver nitrate) solution was used as needle electrode to grow water trees in polyethylene. It was found that during the formation of water trees, silver ions, due to having low free energy of oxidation and reduction, are reduced into metallic silver which is deposited in the channels of water trees. This process is like electroplating, so the channels of water trees still remain after removal of electric field. It was observed by means of an SEM that there do exist microchannels in a water tree with their diameters being from 02 to 0.5 μm. Based on this discovery, a possible model on the microstructure of a water tree is suggested. In this model the two models above-mentioned are unified