Controllable Preparation And Toughening Mechanism Of Graphene/Alumina Composites

Alumina ceramics have attracted wide attention because of their excellent mechanical properties and high temperature resistance.However,the intrinsic brittleness of alumina ceramics limits its application in many fields.Therefore,many researchers have carried out fruitful research on how to improve the toughness of alumina ceramics.In this paper,graphene reinforcement with excellent mechanical properties was added to alumina matrix,and the effects of graphene content and arrangement on the microstructure and toughness of alumina ceramics were studied.In this paper,the alumina ceramic particles and the graphene oxide slurry are uniformly mixed by the liquid phase mixing method,and the water in the mixed liquid and solid phases is converted into ice by the method of ultra-fast freezing,and the graphene oxide and the alumina ceramic particles are fixed.Subsequent removal of ice by lyophilization method obtained a mixed powder of alumina ceramic particles and graphene oxide,hydrogen was used to reduce graphene oxide to graphene,and in-situ densification was used to prepare graphene/alumina composite material.Microstructure shows that graphene is randomly distributed in alumina ceramics and graphene is evenly distributed in the matrix.With the increase of graphene content,the fracture toughness of the composite increases first and then decreases.When graphene content is 0.3 vol%,the fracture toughness(K_IC)of the composites is the highest,reaching 6.8MPa·m^1/2,and the bending strength increases to 421 MPa.Compared with pure alumina ceramics,the fracture toughness increases by 37%and the bending strength increases by 7%.At the same time,the results show that the compactness and conductivity of nanocomposites are obviously different by different sintering methods.The densification of nanocomposites is better by spark plasma sintering.The densification of composites with graphene content of 10 vol%is as high as 96%.The addition of graphene greatly improves the electrical conductivity of alumina ceramic composites.With the increase of graphene content,the electrical conductivity increases gradually.When the graphene content is 10 vol%,the prepared composites have the highest conductivity,up to 4.13×10³ S/m,While the alumina matrix is typically electrically insulating.Based on the above work,by using graphene oxide and alumina monohydrate as raw materials,the direction of water crystallization can be effectively controlled by changing the freezing speed and controlling the temperature field,so that the arrangement direction of graphene oxide can be effectively controlled.After drying and reduction,a graphene/monohydrate alumina composite sponge was obtained,and the dense alumina ceramic composite material was prepared by hot pressing sintering.The results show that the nanocomposite has a layered structure,and the graphene is arranged in the composite material without agglomeration.The layered composites material have excellent toughness.When the graphene content is 4 vol%,the fracture toughness(K_JC)of the composite material is as high as 22.0 MPa·m^1/2,which is 7 times higher than that of pure alumina ceramics.The results of scanning electron microscopy show that the crack propagation path is tortuous,which is caused by the ordered arrangement of graphene in the matrix,which hinders the crack propagation and prolongs the path of crack propagation.This layered nanocomposite also has a high modulus?287 GPa?and excellent electrical conductivity?⁸25 S/m?.The results also show that as the graphene content increases,the fracture toughness of the composite increases first and then decreases.