Influence of ions on the growth of water trees

Results of experiments using the water needle method in low-density polyethylene specimens are reported. The relation between the growth of water trees and the concentration of ions in the solution is studied quantitatively within a wide range. The growth of water trees consists of two aspects: expansion of the zone of the water tree and structure deterioration in the zone of the water tree. The influence of the kind of ions may be as large as that of its concentration in both aspects. Moreover, it seems that certain kinds of additional ions could inhibit the normal growth of water trees. It is found that the growth of water trees correlates with the absolute hydration entropy of ions; in particular, the lowest propagation rates are obtained with high valence, for example Fe⁺ and Al³⁺