Effect of water on the diffusion of small molecular weight acids in nano-SiO2 modified insulating oil

Abstract

The diffusion of water and organic acids in insulation affects each other. This effect is more complicated for the situation of nano-SiO2 modified insulating oil than for traditional oil. Formic acid has the largest influence on the oil-paper insulation system; therefore, the diffusion of formic acid in nano-SiO2 modified insulating oil with different initial water contents was studied through the experiment. It was found that the binding of nano-SiO2 modified insulating oil to formic acid increased with increasing water content. Diffusion models for formic acid in nano-SiO2 modified insulating oil with varying water contents were established via molecular dynamics. The adsorption models of formic acid on the nano-SiO2 (001) surface were determined via DFT calculations. The results of the molecular dynamics simulations showed that a higher water content resulted in weaker diffusion of the formic acids. This resulted in a decrease of the mean square displacement and an increase of the diffusion activation energy of the formic acids. The effect of water on formic acid could mainly be attributed to two aspects: the binding of water and the strengthening effect of water on the adsorption ability of the nano-SiO2 for formic acid. This work can contribute to determining the behavior of formic acid in nano-modification.