Preparation And Properties Of Graphene/Alumina Based Coaxial Structure Composite Ceramics

Nuclear power is a kind of green energy with high energy density,clean and low carbon,but the Fukushima nuclear power plant accident has caused people’s concern about nuclear safety.Among them,the electrical penetration assembly（feedthrough）is used to connect the devices in the reactor,and its reliability in high temperature and high pressure environment is one of the key elements to ensure the safe operation of nuclear power plants.At present,the feedthrough wires of nuclear electrical penetration assemblies are still mainly made of aluminum,copper and other metals as the inner core conductive materials,and high resistivity ceramics as the insulating layer;At the same time,one or more transition layers are added between metal and ceramics,and the air tightness of electrical penetration assemblies is ensured by brazing and sealing.However,due to the weak corrosion resistance of metals,there are differences in the expansion coefficients between metals,ceramics and transition layers.When the temperature and pressure rise abnormally,problems such as interface failure and air tightness decline may occur,which buried hidden dangers for the leakage of radioactive substances when the accident occurred.Aiming at a series of problems of feed through wire of electrical penetration of metal/ceramic structure in extreme service environment,this topic creatively designs the feed through wire of coaxial structure based on graphene/alumina composite ceramic,in which graphene/alumina composite ceramic is used as the conductive core and alumina ceramic with high resistivity is used as the insulating layer.Alumina ceramics have very high resistivity（1015 Ω· cm）and good mechanical properties at high temperature.They are often used as insulating layer at high temperature.In addition,graphene has extremely high conductivity（1 × 106 s/m）,which is widely used to regulate the electrical and mechanical properties of structural ceramics.Therefore,using graphene/alumina composite ceramics as the conductive inner core is expected to achieve controllable regulation of the conductivity of the feedthrough line.In this work,the preparation method of the feedthrough line with coaxial structure: first,the graphene oxide solution with a high degree of oxidation can be prepared by using the improved hummers,which is mixed with the alumina solution,and the graphene oxide and alumina powder are uniformly dispersed by heterogeneous deposition.The graphene oxide/alumina composite powder is obtained by drying in the oven,and then the green body with a diameter of 5 mm is prepared by dry pressing,and then embedded in the alumina powder,Then,through dry pressing,the green body with coaxial structure with a diameter of 10 mm is prepared;Finally,graphene/alumina composite ceramics with coaxial structure were obtained by SPS sintering.The influence of graphene content on graphene/alumina composite ceramics was studied in this paper.The density and bending strength of graphene/alumina composite ceramics gradually decreased with the increase of graphene content,but the conductivity gradually increased to 2455s/m.Compared with graphene/alumina composite ceramics,graphene/alumina composite ceramics with coaxial structure have higher bending strength,which is mainly due to the residual stress between alumina ceramics and graphene/alumina composite ceramics.