Preparation and Dielectric Properties of Inorganic Compound Nanoparticles Hybrid PI and Composite Films

Author:Wang Xiang Wen

Supervisor:fan yong

Database:Doctor

Degree Year:2018

Download:86

Pages:123

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Polyimide materials are widely used in power electronics,aerospace and automotive applications due to their excellent mechanical,electrical and mechanical properties.In recent years,wide range of applications of variable frequency motor,the higher requirements for the corona resistance propertiy of the insulation material have been needed.The polymer modified by nanomaterials have become an important research area of dielectric material.The dielectric properties of the materials can be improved by the combination of nanoparticles and polyimide to form an appropriate nanostructure and a reasonable composite structure.In this paper,nano Mg(OH)2 and nanometer Zn(OH)2-Mg(OH)2 were prepared by reverse-precipitation method.The nano Al/Si dispersion was successfully synthesized by microemulsion hydrothermal method.Then nano Mg(OH)2/PI,nano ZnO-Mg(OH)2/PI and nano Al2O3/PI hybrid films were successfully synthesized,three-layer nano A/M/A type polyimide composite film and three-layer nano A/Z/A type polyimide composite film.The properties of films were tested and analyzed,The influence mechanism of the dielectric properties and the corona resistance of the three layer films affect by the change on the properties of the middle layer films were carried out.Within the scope of this experiment,the thermal stability of nano Mg(OH)2/PI hybrid films is less affected by nano Mg(OH)2 particles,with the increasing of the content of nano Mg(OH)2,the volume resistivity decreases,the dielectric constant increases,the loss increases.It shows that the polarization unit in the hybrid film is increased,the introduction of nano particles makes the polarization dispersion of nano Mg(OH)2/PI hybrid film increased.Nano Mg(OH)2 particles increase the aging threshold of the polymer,reduce the accumulation rate of space charge,the inhibition abbility of space charge is enhanced.The enhancement of the inhibition of space charge and the homogenization of the electric field caused by the addition of nanoparticles.Those factors make the probability of the space charge concentration to lead to the formation of a conductive channel reduced.The result show the breakdown field strength of nano Mg(OH)2/PI hybrid films is improved.Compared with nano Mg(OH)2/PI hybrid films,the thermal stability of nano ZnO-Mg(OH)2/PI hybrid films is relatively poor,the volume resistivity is relatively low,the dielectric constant and dielectric loss are relatively small.In the high electric strength,the inhibition ability for space charge current is stronger than nano Mg(OH)2/PI hybrid films.It shows that the depth of trap caused by nano ZnO-Mg(OH)2 particles in the material is deeper.The formation of space charge anti electric field is stronger.The breakdown field strength of the nano ZnO-Mg(OH)2/PI hybrid thin film is higher,it has reached to 298 k V/mm.The dielectric constant and loss of nano A/M/A type polyimide three-layer composite film are in accordance with the general laws of composite dielectric material.The breakdown strength of nano A/M/A type polyimide three-layer composite film is higher than that of single layer film.This is the result of the rational distribution of the electric field between the three layers and the complementation of the interlayer performance.The corona resistance life of the nano A/M/A type polyimide three layer composite film is 77.7 h and 8.6 h respectively at room temperature and high temperature,respectively.It is 55 times and 6.6 times that of pure film,respectively.This is due to the good corona resistance of the Al2O3/PI film,the distribution of the electric field reduces the field strength of the outer layer,and the large volume resistivity of the inner layer weakens the diffusion of electrons in the polymer.It is beneficial to the formation of the space charge anti electric field.At the same time,there is no direct injection of electrode electrons in the middle layer and the comprehensive effect of high breakdown field strength.The combined effect of these factors make the endurance of the corona resistant life increased.The maximum breakdown field strength of the nano A/Z/A type polyimide three-layer composite film is higher than that of the nano A/M/A type polyimide composite film.The nano A/Z/A type polyimide three-layer composite film has a corona-resistant life of 82.95 h at room temperature which is 59.25 times of that of a pure film that have the corona resistance life of 1.4 h.The corona-resistant life at 155℃ is 10.2 h,which is 7.8 times that of the pure membrane,that is longer than the corona resistant life of the three-layer A/M/A type polyimide composite films.There are some reasons for this phenomenon.The dielectric constant of the nano ZnO-Mg(OH)2/PI hybrid thin film is smaller at 50 Hz.So,outer layer of nano Al2O3/PI hybrid films have applied to low field strength,the erosion of the outer layer coused by electric field is relatively reduced.The interlayer of nano A/Z/A type polyimide three layers of composite own higher breakdown field,this decreases the probability of the entire breakdown which caused by intermediate layer breakdown at first.The combined effect of these factors improves the corona resistance life of the nano A/Z/A type polyimide three layer composite film.The rational design of the three layer structure plays an important role in improving the dielectric properties of the materials.This paper provides the theoretical basis and experimental research foundation for the development of high performance corona resistant materials.