Effect of Nonlinear Conductivity Modification on Space Charge Behavior of Modified Epoxy With Inorganic Filler

Abstract

High energy electrons would easily penetrate into spacecraft dielectrics (Epoxy) and accumulate inside, finally causing charge–discharge danger for spacecraft. Nonlinear conductivity modification of epoxy resin (EP) can automatically leak the accumulated charges and prevent charge–discharge from occurring. Inorganic fillers have a significant effect on the nonlinear conductivity characteristics of spacecraft dielectrics (Epoxy). This work reported the nonlinear conductivity modification influence on the space charge behavior of modified EP composite materials. The samples of modified ZnO/EP (MZ) and modified SiC/EP (MS) composite materials were prepared. The nonlinear conductivity experiment was carried out, and the results showed that: 1) the nonlinear electric-field thresholds of MZ and MS were 1.70 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{7}$</tex-math> </inline-formula> and 1.54 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{7}$</tex-math> </inline-formula> V/m, respectively; and 2) as the applied electric field rose from low level to high level, the average conductivity value of MZ increased from 3.24 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-13}$</tex-math> </inline-formula> to 6.27 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-12}$</tex-math> </inline-formula> S/m, and that of MS increased from 4.97 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-13}$</tex-math> </inline-formula> to 2.77 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-11}$</tex-math> </inline-formula> S/m. The space charge test results showed that: 1) the space charges inside MZ were positive, whereas they were negative inside MS and 2) as the applied electric field increased from 10 to 20 kV/mm, the peak value of space charge density of MZ decreased from 0.17 to 0.01 C/m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{3}$</tex-math> </inline-formula> . The space charges inside MS could decrease closer to 0 rapidly under high electric field (20 kV/mm). Finally, the mechanism of inorganic fillers affecting the space charge distribution of modified EP was investigated, because the bandgap of SiC is narrower than that of ZnO, electrons can have a high-drift speed during transporting process; the transportation speed of electrons inside MZ was higher than that of holes, and ZnO addition led to the mass production of high trap densities and high energy levels inside MZ, so the space charge distribution of MZ was different with that of MS. The findings of this study confirmed that the modified EP composite materials (MZ and MS) both showed obvious nonlinear conductivity characteristics, and they were excellent potential materials for spacecraft to effectively leak away the accumulated space charges of dielectrics in space.