Tiaotiao Chen’s research while affiliated with Tongji University and other places

In order to provide further evidence for the improvement in tracking and erosion resistance of alumina trihydrate (ATH)-free silicone rubbers (SRs) by direct fluorination and to explore the improvement mechanisms, the ATH-free SR samples containing 15-parts per hundred parts of rubber by weight (phr) melamine cyanurate and 18-phr fumed silica were prepared, and then they were surface fluorinated using a $\text{F}_{{2}}/\text{N}_{{2}}$ mixture at 0.1 MPa and 85 °C for 120 min. Inclined plane tracking and erosion tests indicate that at 4.5-kV rms ac, all 15 fluorinated samples passed the test, while 7 of the 15 unfluorinated samples failed the test due to combustion. Analyses of erosion depth, length, and area show that the fluorinated sample, compared to the unfluorinated sample, has a larger average erosion depth but a smaller average erosion length or area. Attenuated total reflection infrared spectroscopy (ATR-IR) and X-ray photoelectron spectroscopy (XPS) analyses indicate that both the SR matrix and the fillers of melamine cyanurate and fumed silica in the surface layer were fluorinated, forming the Si–F, C–F, and N–F bonds. Scanning electron microscopy (SEM) observations show that the fluorinated layer has a thickness of $1.15~\mu \text{m}$ and a rough surface, and the fillers are uniformly dispersed in the matrix. The resistance improvement by the fluorination is attributed to these changes of the surface layer in composition, structure, and interface of the SR matrix and the fillers and is also influenced by the change in surface morphology.

Liquid silicone rubber (LSR) sheet samples of a commercial formulation and surface fluorinated using a F 2 /N 2 mixture at various temperatures are studied in this work. The intrinsic DC flashover of the surface fluorinated samples is evaluated using a sheet sample/finger electrode configuration and under a stepwise increasing voltage. The tests show an increase up to 64% in the intrinsic DC flashover voltage of the LSR by the fluorination and an influence on the flashover on the fluorination temperature. ATR-IR and XPS analyses indicate that there are Si-F bonds as well as C-F bonds in the fluorinated layers. SEM shows the thickness of the fluorinated surface layers with nanostructured surfaces. Surface conductivity and potential decay measurements reveal that the fluorination caused a large increase in surface conduction, in association with fluorination temperature. The improvement in the intrinsic DC flashover is mainly attributed to the suppression of surface charge accumulation on the LSR by the increased surface conduction.