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Under different environmental relative humidity (RH), the corona resistance of polyimide film presents significant differences. In order to understand the effects of RH on the surface corona characteristics and ageing process of film, we monitored the corona discharge process, electrical properties, and surface morphology of the film under different RH, and obtained the effects of RH on the corona ageing of film. The results show that with the increase of RH, the changing trends of the discharge activity at positive and negative half cycle are opposite. When the RH is equal or less than 69%, both the discharge quantity and discharge frequency show rapid growth stage, stationary stage, and secondary development stage with corona time, and when the RH attains 84%, both of them increase linearly with time. The changing rate of moisture content (Δwt%) of the film increases significantly at the beginning of corona ageing and tends to be stable at the middle and later periods, and when the RH attains 84%, the Δwt% increases linearly with the ageing time. It is analyzed that the surface electrothermal damage of film caused by corona discharge is the main cause of the rapid decrease of surface resistivity (ρs). With the corona erosion, water penetrate into the film gradually, eventually leading to the sharp decrease of ρv till breakdown.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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