Utilization of positron annihilation and electrochemical impedance to study the microstructure variations and water diff

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Utilization of positron annihilation and electrochemical impedance to study the microstructure variations and water diffusion of NO2-oxidative-damaged silicone rubber Jinshuai Zhang1, Zheng Wang1,2, Yi Luo1, Libing Qian1, Chunqing He1, Ning Qi1, Pengfei Fang1,* , Zhen Huang2, and Xiangyang Peng2 1 2

Department of Physics and Hubei Nuclear-Solid Physics Key Laboratory, Wuhan University, Wuhan 430072, China Guangdong Key Laboratory of Electric Power Equipment Reliability, Electric Power Research Institute of Guangdong Power Grid Co., Ltd, Guangzhou 510080, China

Received: 15 September 2020

ABSTRACT

Accepted: 9 November 2020

Silicone rubber is widely used in power grids, electronics and aerospace, because of its hydrophobicity, high flexibility, etc. However, it is susceptible to some environmental chemical factors, such as NO2 and ozone, which can induce chain scission, the generation of defects and the ingress of water. In this work, we systematically studied the microstructure variations and water diffusion behavior of high-temperature vulcanized (HTV) silicone rubber after NO2-induced oxidative damage. Microstructure evolution in silicone rubber was investigated by positron annihilation lifetime spectroscopy (PALS). The results show that the oxidation of NO2 significantly degrades organic matrices, which induces the decrease of crosslinking degree and the formation of defects compared to virgin samples. The water transportation was evaluated by electrochemical impedance spectroscopy (EIS), which showed that the diffusion coefficient, under the NO2 concentration of 28.75 mg L-1, is 106 times that of virgin sample with a water uptake of 31%. Particularly, when the concentration reaches the critical value around 17.25 mg L-1, the diffusion coefficient and water uptake increase sharply, and the calculated average porosity of samples also dramatically increases by 4 orders of magnitude. These indicate the formation of more nano- and micron holes, serving as a pointer for percolation of defects in silicone rubber bulk. The study of microstructure variations and water transportation can help us to understand the aging mechanism, design reasonable composite polymer materials and prevent the damage of chemical contact.

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Springer Science+Business

Media, LLC, part of Springer Nature 2020

Address correspondence to E-mail: [email protected]

https://doi.org/10.1007/s10854-020-04867-6

J Mater Sci: Mater Electron

1 Introduction Silicone rubber is one of the most important organic polymer sealing materials. The demand for highstability silicone rubber is growing rapidly due to the practical applications in aerospace [1, 2], electronics [3, 4], medical devices [5, 6] and high voltage outdoor transmission lines [7–9]. However, in the harsh external environment, the sealing materials of equipment are prone to aging and failure. In recent years, the aging of silicone rubber has been extensively studied in salt fog [10], ultraviolet radiation [11, 12] or high temperature [13]. For example, the corona discharge can result