In this paper, the permeation properties of three types of liquids into HTV silicone rubber with different Alumina Tri-hydrate (ATH) contents had been investigated by weight gain experiments. The influence of differing exposure conditions on the diffusion into silicone rubber, in particular the effect of solution type, solution concentration, and test temperature were explored. Experimental results indicated that the liquids permeation into silicone rubber obeyed anomalous diffusion ways instead of the Fick diffusion model. Moreover, higher temperature would accelerate the permeation process, and silicone rubber with higher ATH content absorbed more liquids than that with lower ATH content. Furthermore, the material properties of silicone rubber before and after liquid permeation were examined using Fourier infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM), respectively. The permeation mechanisms and process were discussed in depth by combining the weight gain experiment results and the material properties analyses.
Long-term liquids diffusion tests were performed on glass fibre reinforced polymer (GFRP) used in high voltage composite insulator. The plate-shaped GFRP specimens were immersed in three types of liquids, which high voltage composite insulator would encounter in practice, including deionised water, NaCl solution and nitric acid solution for a period of 4000 h. Chemical reaction and physical dissolution complicated the diffusion processes, which could be divided into three types based on the features of diffusion curves. Fourier transform infrared spectroscopy, scanning electron microscopy and optical interferometry were employed to investigate the chemical property, two-dimensional (2D) and 3D surface morphologies of GFRP. The results revealed that the surface layer of GFRP was destroyed to some extent depending on the type and concentration of the liquid, the maximum of profile height deviation of GFRP surface was proposed to evaluate the extent of the corrosion of GFRP, the greater the profile height deviation, the more serious the corrosion of GFRP. The present work is helpful for a better understanding of the diffusion behaviour of liquids into GFRP used in high voltage composite insulator as well as in other industry applications.
High-temperature vulcanised (HTV) silicone rubber composite insulator has been widely used in extra-high and ultrahigh transmission lines due to its excellent electrical and mechanical performance. In practice use, liquids may encounter the composite insulator intermittently and can lead to the degradation and deterioration of silicone rubber. In the present research, the effects of liquids immersion and subsequent drying on the surface properties of HTV silicone rubber were investigated by means of the contact angle measurement and surface physical morphology measurement which was further analysed in terms of the discrete wavelet transform method, multiresolution signal decomposition algorithm, and three-dimensional fractal dimension calculation. Based on the experimental results, the mechanism of the loss and recovery of the hydrophobicity of HTV silicone rubber surface during the liquids immersion and subsequent drying processes were further explained by taking into consideration the embedded water molecules (and/or hydrated ions) on the HTV silicone rubber surface and the synergy of the increase in roughness/fractal dimension and low molecular weight siloxanes diffusion. This study is helpful for better understanding of the change of surface properties of HTV silicone rubber caused by environmental and electrical stresses.
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