Research On The Dielectric Properties Of Composites Based On Inorganic Powders

Inorganic powders are common dielectric materials in the power industry.Because of their excellent chemical stability and electrical insulation properties,they are often used as inorganic fillers to improve the performance of organic polymers.And excellent heat dissipation and high temperature resistance also make them be widely used in the manufacture of mineral cables and electrical ceramics.Therefore,the research on the dielectric properties of inorganic powder is of great value for their subsequent application.Four kinds of inorganic powders such as alumina（Al₂O₃）,magnesia（Mg O）,silica（Si O₂）,boron nitride（BN）were taken as the research object for the purpose of basic research.The composites were prepared by physical bonding of inorganic powder with organic resin.The electrical conductivity under variable temperature and breakdown characteristics of the inorganic powders and the inorganic powders/organic resin were respectively studied,the effect of powder morphology on the dielectric properties of the composites was analyzed.The results show that the volume conductivity of inorganic powders and the inorganic powders/organic resin composites increases with the increase of temperature and external electric field strength.This is because the increase of temperature and external electric field strength will increase the number of carriers in the medium,which is consistent with the classical dielectric theory.Under the same temperature and external electric field strength,the volume conductivity of the inorganic powders before bonding decreases with the increase of the particle size,while that of the composites increases with the increase of the particle size.The conductivity of the composites based on inorganic powders is significantly lower than that of the same inorganic powders.At the same temperature,the breakdown field strength of the inorganic powders decreases with the increase of the particle size,while that of the composites decreases with the increase of the particle size.The breakdown strength of the composites based on the same particle size is significantly higher than that of the same inorganic powders.This is because the internal air gaps of the composites are effectively filled,and a large number of organic-inorganic interfaces are introduced,and the energy level of the interface traps is increased,so that the ability of inorganic powders to withstand external field strength is enhanced.For the composites with epoxy resin as binder,after the surface modification of Kh-550 with a mass fraction of 3%,the affinity between the inorganic powders and the organic phase is enhanced,and the dispersion of the organic resin in the inorganic powders is improved.Under the same test conditions,the volume conductivity of the composites based on the Al₂O₃,Mg O and Si O₂ further decreases,and the breakdown field strength increases.In order to explore the influence of inorganic powder morphology on the dielectric properties of its composites,this thesis also compares the conductivity under variable temperature and breakdown characteristics of the composites based on the spherical and irregularly shaped powders.The results show that the composites based on the spherical powders have lower volume conductivity and higher breakdown field strength under the same test condition.This is because the irregularly polygonal powder particles have obvious edges and corners in the microstructure,and the gaps between the particles are difficult to be uniformly filled by the organic resin,resulting in an uneven electric field inside the medium.While the gaps of the spherical powder particles are filled more fully by the organic resin,and the electric field distribution inside the medium is more uniform.