Research On Space Charge Characteristics In Micro/nano BiFeO₃/LDPE Composites

Due to defects and impurities in polymer materials,a large amount of space charges accumulate in the interior,resulting in internal electric field,changing the distribution of electric field in the material,causing distortion of electric field,affecting its service life and safety.Therefore,suppressing the accumulation of space charges in materials has become a necessary concern.Through a large number of studies,it is found that doping a small amount of inorganic micro-nano particles into low density polyethylene（LDPE）can significantly improve the space charge accumulation inhibition of LDPE and improve its dielectric properties.At the same time,because the external field（magnetic field,microgravity field,etc.）can improve the properties of polyethylene,it has become a promising research method to control the properties of polymer materials by magnetic field treatment.In this paper,LDPE was applied as the matrix to prepare composites with BiFeO₃content of 0.2wt%,0.5wt%,1wt%and 2wt%by doping micro-nano bismuth ferrate（BiFeO₃）grains,separately.The composites were processed by a steady magnetic field and subjected to scanning electron microscope（SEM）,X-ray diffraction（XRD）,difference scanning calorimetric analysis（DSC）and other techniques to characterize the micro-and nanocomposites.The findings indicate that the composites doped with BiFeO₃ particles have improved particle dispersion after magnetic field treatment,and the aggregation morphology in the LDPE matrix is changed as a result of different particle shapes.The doping of BiFeO₃ particles can make the crystallinity of the composites increase,and the magnetic field effect also increase the crystallinity of LDPE and the composites.This is due to the nucleation of BiFeO3＿3 particles and the regular alignment of LDPE molecular chains by magnetic field,which improves the crystallinity.Meanwhile,the magnetic performance（VSM）test demonsteated that the larger the particle size of doped BiFeO₃ particles,the poorer the hysteresis line nonlinearity and the weaker the saturation magnetization intensity of the magnetized material.In this paper,the dielectric performance and space charge attributes of the magnetic field-treated composites were tudied and investigated.The dielectric properties,breakdown performances,and space charge performance of the composites mixed with micro-and nano-BiFeO₃particles are dependent on the dimensions of the doped BiFeO₃ grains,the shape of the grains,and magnetic field treatment at 1.5T.（1）After magnetic field treatment,the dispersion of BiFeO₃ particles in BiFeO₃/LDPE composites is improved,which makes the interface area,polarization and dielectric constant increase.After magnetic field magnetization,the dielectric loss of nanocomposites decreases,and the micron composite’s still has a relatively small dielectric loss.Under the AC field,the breakdown field strength of the room temperature magnetized composites is enhanced,and the breakdown field strength of the micron composites after high temperature magnetization is reduced.It may be caused by the breakdown field strength is effected on the size of doped particle size and material aggregation morphology.（2）The composites mixed with BiFeO₃particles have a good effect of suppressing space charge accumulation.After the magnetic field treatment,the performance of the composites in inhibiting space charge accumulation was enhanced,and the space charge content in LDPE was diminished.For the nanocomposites,the properties of space charge accumulation were enhanced and then decreased with the doping concentration of BiFeO₃,and the best performance was obtained at 1 wt%.Upon magnetic field treated,the particle dispersion was modified and the formation of interfacial regions was enhanced for space charge suppression,which limited the space charge accumulation in the composites.For micron composites,the morphology of the doped micron particles and the aggregation morphology formed with the LDPE matrix have different effects on the space charge suppression performance,and the doping of micron particles with spherical structure is more effective for the suppression of space charge accumulated in the composites,and the lamellar structure having more space charge content in the micron composites.