270 / 2018-09-25 09:26:24

Study on Polarization and Depolarization Characteristics of BaTiO3/Epoxy Nano-composites

nonlinear,dielectrics,epoxy composites,polarization,depolarization

Nonlinear insulating material has field-dependent susceptibility and/or conductivity and can regulate the nonuniform electric field distribution, so it is called as "smart insulating material". It has been widely used in the motor anti-corona structure and cable accessory structure and has a good prospect in the HVDC insulation system and pulse power technology insulation system. Due to the complexity of nonlinear problems, the researches on dielectric characterization and measurement of nonlinear insulating materials are rarely reported. Based on a new physical model proposed by our group, the dielectric response characteristics of nonlinear insulating materials are studied under DC voltage in this paper.
Epoxy resin is widely used in high voltage electrical equipment due to its good corrosion resistance, insulation and mechanical properties. In this paper, a bisphenol-A epoxy resin (PHOENIX WSR618 E-51) and a methyltetrahydrophthalic anhydride (GH-9303) are chosen as the polymeric matrix and the hardener, respectively. A 2, 4, 6-tris (dimethylaminomethyl) phenol (DMP-30) is selected as the accelerator. The materials mentioned above are mixed in weight ratio of 100: 80: 1. Barium Titanate(BaTiO3) is a kind of wave-absorbing ceramic material with high capacitance and low dielectric loss and it exhibits ferroelectric properties after polarization. The nano-composite preparation is realized by adding nano-particles into the epoxy matrix. The surface treatment of BaTiO3 nano-particles was carried out with a silane coupling agent (KH550) at first. The nano-composites are cured at 80 ° C for 4h and then post-cured at 120 ° C for 8h. The filler loading of nano-composites are 0, 0.5, 1, 3 and 5 wt%.
The nano-composites are characterized by scanning electron microscopy (SEM). The surface treatment effect of the coupling agent on BaTiO3 particles is analyzed by infrared spectroscopy. The polarization and depolarization time-domain current spectrum of BaTiO3/epoxy nano-composite are obtained by Keithley6517B high-resistance meter.
The SEM figures show that the BaTiO3 nano-particles are dispersed uniformly. According to infrared analysis, the coupling agent KH550 is confirmed to be connected with BaTiO3 nano-particles. By applying different field strength, the polarization and depolarization process are recorded. The filler loading barely affected the polarization characteristics under low field, whereas it has a great effect on the polarization characteristics under medium and high field. Based on the Debye model hypothesis, the I(t)t--lg(t) curve is plotted for the depolarization time-domain current spectrum of the samples with different filler loadings for different electric field strength, and the distribution of relaxation peak is obtained, the difference between relaxation peak and peak width can reflect the relaxation process. The structure of the prepared sample is plate type, and the peak point distribution is equal to the relaxation time constant under the DC steady-state voltage, and the peak width increases obviously with the increasing filler loading under the same electric field strength. According to the experimental data and equivalent model, the correlation relaxation parameters are obtained and the influences of filler loading on the parameters are analyzed.
In this paper, the effects of filler loading on dielectric properties of epoxy nano-composites are analyzed by measuring the polarization and depolarization time-domain current spectrum. This work is very helpful for understanding the dielectric characteristics of nonlinear insulating materials.