研究目的
to contribute to high voltage characterization of epoxy – h-BN microcomposites
研究成果
The addition of micro h-BN to the epoxy matrix leads to an improvement of many properties amongst the one required for high voltage insulation. Thermal properties are improved while dielectric breakdown strength is enhanced and dielectric properties remain almost unaltered. Ep-30BN shows an overall reduction of apparent charge carriers mobility compared to neat epoxy. For both materials, the current is ohmic at low field and a SCLC mechanism has been proposed at high fields. Ep-30BN has a higher threshold field from ohmic to SCLC regions, which could lead to a better withstand of electrical stress.
研究不足
The study does not explore the effect of varying the h-BN filler loading on the electrical properties. Space charge measurements would be necessary to better interpret the SCLC behavior. Further measurements as a function of sample thickness and electrode material would be interesting to confirm the limiting mechanisms.
1：Experimental Design and Method Selection:
The study focuses on the DC conductivity and AC breakdown strength of epoxy composites filled with 30 wt% of micron sized hexagonal boron nitride (h-BN) compared to neat epoxy. The influence of h-BN upon the field dependence of DC conductivity was studied up to 18 kV/mm. AC breakdown strength measurements were performed at room temperature.
2：Sample Selection and Data Sources:
The epoxy system consists of a diglycidyl ether of bisphenol A (DGEBA) prepolymer crosslinked with an anhydride hardener. Hexagonal boron nitride particles used are micron sized platelet particles provided by Momentive.
3：List of Experimental Equipment and Materials:
Planetary mixer SpeedMixer DAC400, aluminum mold treated with a release agent, gold electrodes sputtered at the surface of the samples, transformer vegetal oil (Envirotemp? FR3? provided by Cooper).
4：Experimental Procedures and Operational Workflow:
The dispersion of h-BN in each reactant was performed using a planetary mixer. The reactive blend was mixed, degassed under vacuum, cast into an aluminum mold, cured, and post-cured. DC conductivity measurements were carried out at 60 °C from 2 kV/mm to 18 kV/mm. AC breakdown voltage measurements were performed at room temperature.
5：Data Analysis Methods:
Current values at 10 h of polarization were obtained by fitting the experimental data to remove measurement noise. A two-parameter Weibull distribution was used to analyze the AC breakdown strength results.
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