The Preparation Of Sheet-like Magnesium Oxide And Application In Dielectric Composites

In this paper,sheet-like MgO powders prepared and modified are used as inorganic fillers.Through experiments and simulation studies,the purpose is to improve the room temperature and high temperature energy densities of PVDF-based and PEI-based composites.The reasons for the improvements of energy densities are analyzed preliminary in this paper.Sheet-like MgO powders are prepared by hydrothermal synthesis combined with calcination treatment.Taking the breakdown strengths of composites as the target,the optimal hydrothermal time and ammonia concentration are optimized by single factor variable method,which are 24 h and 20 wt.%respectively.The prepared MgO powders are sheet-like with a transverse size of about 400 nm and a thickness of about 40 nm.When the powder content is 2.8 wt.%,the energy density of MgO/PVDF composites reaches 16.9 J/cm3 at room temperature,which is more than 80%of the PVDF matrix,indicating that the MgO with sheet-like morphology is helpful to increase the energy densities of the composites.Using PEI as matrix,the effect of MgO powder addition on the energy densities of PEI matrix composites with temperature is studied.The results show that the energy densities of the composites decrease with the increase of temperature.When the addition amount of 3.4 wt.%MgO is added,the energy density of the composites is better at 25℃ and 150℃,which are 5.54 J/cm3 and 3.79 J/cm3,respectively.Due to the poor compatibility between MgO and PEI matrix,the breakdown strengths decrease obviously with the increase of temperature.Therefore,silane coupling agent KH550 is used to modify the surface of sheet-like MgO powders.The optimal content of the modifier is determined as m(KH550):m(MgO)=3:100.When the content of m-MgO is 3.0 wt.%,the energy density of m-MgO/PEI composites can reach 6.10 J/cm3 and 5.18 J/cm3 at 25℃ and 150℃,which is 10%and 8%higher than that before modification,respectively.The results indicate that KH550 is an effective modifier to improve the energy densities and temperature stability of MgO/PEI composites.The reason is that the-NH2 and-OC2H5 of KH550 form hydrogen bonds with the hydroxyl groups on the surface of MgO and PEI molecules,respectively,which enhances the compatibility of organic-inorganic materials.Finite element simulation method and COMSOL Multiphysics software are used to simulate the internal electric field distribution of sheet-like MgO/PVDF composites.The effects of the contents and sizes of sheet-like MgO,the orientation and dispersion degree of MgO in PVDF matrix on the internal electric field distribution of composites are studied.The results show that the breakdown strengths of sheet-like MgO/PVDF composites increases first and then decreases with the increase of sheet-like MgO powder contents,and there is an optimal powder content.The larger the transverse size and the thinner the thickness of the sheet-like MgO powders,the stronger the pressure resistance of the composites.When the MgO fillers are distributed parallel to the electric field direction,the high voltage resistance of the composites is weak.The more evenly dispersed MgO fillers in PVDF matrix,the better the pressure resistance of the composites.The simulation results confirm the experimental results of MgO/PVDF composites.