Improving the surface flashover performance of epoxy resin by plasma treatment: a comparison of fluorination and silicon deposition under different modes

Abstract

This work treats the Al 2 O 3 -ER sample surface using dielectric barrier discharge fluorination (DBD-F), DBD silicon deposition (DBD-Si), atmospheric-pressure plasma jet fluorination (APPJ-F) and APPJ silicon deposition (APPJ-Si). By comparing the surface morphology, chemical components and electrical parameters, the diverse mechanisms of different plasma modification methods used to improve flashover performance are revealed. The results show that the flashover voltage of the DBD-F samples is the largest (increased by 21.2% at most), while the APPJ-F method has the worst promotion effect. The flashover voltage of the APPJ-Si samples decreases sharply when treatment time exceeds 180 s, but the promotion effect outperforms the DBD-Si method during a short modified time. For the mechanism explanation, firstly, plasma fluorination improves the surface roughness and introduces shallow traps by etching the surface and grafting fluorine-containing groups, while plasma silicon deposition reduces the surface roughness and introduces a large number of shallow traps by coating SiO x film. Furthermore, the reaction of the DBD method is more violent, while the homogeneity of the APPJ modification is better. These characteristics influence the effects of fluorination and silicon deposition. Finally, increasing the surface roughness and introducing shallow traps accelerates surface charge dissipation and inhibits flashover, but too many shallow traps greatly increase the dissipated rate and facilitate surface flashover instead.

Thermally Stable and Dendrite‐Resistant Separators toward Highly Robust Lithium Metal Batteries

“…According to the high‐resolution F 1s spectrum of F‐PPTA@PP separator, the two main peaks located at 686.7 and 688.1 eV correspond to CF and CF x ( x = 2 and 3) bonding, respectively (Figure S7c, Supporting Information), indicating that the CF bonds are the primary F‐containing groups existing on the F‐PPTA@PP separator. [ 45–46 ] CF bond, as the strongest single covalent bond (488 kJ mol –1 ), [ 31 ] is able to not only provide maximum charge polarization for enhancing electrochemical activity of energy‐related reactions, [ 32 ] but also significantly improve the electrolyte affinity of separators. [ 47 ] As proven in the insets of Figure 2a–c, the electrolyte contact angle on the F‐PPTA@PP separator (18.5°) was significantly smaller than that on the PPTA@PP (40.5°) and PP (44.1°) separators.…”

Surface flashover in 50 years: Theoretical models and competing mechanisms

“…Effects of shallow traps on surface flashover: Shallow surface traps are also a crucial factor influencing surface flashover. Xie et al [168] used an atmospheric pressure plasma junction (APPJ) method to fluorinate and deposit Si on epoxy/Al 2 O 3 composites. They found that the energy depth and density of deep surface traps decrease while the energy depth of shallow surface traps decreases, but their density increases as the treatment time increase, causing an increase in DC surface flashover with the treatment time.…”

“…(a) Schematic of the energy band structures of polymeric materials [77]. (b) Relationships between V f and surface trap parameters, that is, (b‐i) deep surface trap level [70, 71, 114, 167], (b‐ii) deep surface trap density [71, 95, 114, 167], (b‐iii) shallow surface trap level [71, 145, 152, 160, 168], and (b‐iv) shallow surface trap density [71, 145]. (c) ‘U‐shaped’ dependence of V f on surface trap level.…”

“…In region II, surface flashover exhibits a negative dependence on the energy depth of traps but depends positively on the density of shallow surface traps and surface conductivity. The surface modification methods in region II includes fluorination [143–146, 176], plasma deposition [150–153, 168, 177], non‐linear conductive material coating [138, 139, 141, 154, 155], ozone treatment [148, 149], (III) Region dominated by leakage current. When surface conductivity exceeds a critical value, the leakage current through the surface increases rapidly, which degrades the insulation properties of materials and decreases surface flashover voltage.…”

Multi‐modified epoxy insulation with improved flashover threshold for HVDC applications

“…The declined charge density and accelerated carrier mobility were the main outcomes of their research which proves the effectiveness of fluorination to improve the insulation strength of polymer dielectrics. Similarly, Y. Huang et al and J. Yan et al adopted electron beam and plasma treatment methods, respectively, to alter the surface condition of epoxy composites [16,17]. The authors claimed that the augmented roughness and conductivity of the surface were obtained after plasma modification and were the key factors to reduce the charging capability of epoxy composites.…”