Study On Thermal Expansion And Mechanical Properties Of 3D Graphene-based Nano-ceramic Composites

Ceramic composites are composed of ceramic materials and other materials,which can maintain the advantages of different material properties and improve the comprehensive properties of single material.Ceramics have excellent properties such as light weight and high strength,stiffness,temperature resistance and corrosion resistance,but also have the disadvantages,such as high brittleness and easy to be fractured,while graphene has excellent mechanical and thermal properties,which can make up for the disadvantages of mechanical properties of ceramic materials.Graphene ceramic composites can be widely used in aerospace,civil engineering,electronic communication and many other fields.At present,graphene ceramic composites have some problems,such as poor molding effect,complex preparation process and the mechanical properties are not ideal,which limit their further application.This research is based on hydrothermal synthesis method and using three-dimensional graphene aerogel as the substrate,the controllable preparation,mechanical and thermal expansion properties of nanometer ceramic composites were studied,including the following three aspects:（1）Based on the hydrothermal synthesis method,by adjusting the composite material preparation technology parameters for 3D graphene controllable preparation of nano ceramic composites,through the analysis of the microscopic characterization of preparation parameters on the microstructure of composites influence the experimental results show that the ZrW₂O₈ precursor solution concentration and the concentration of HCl solution affect the growth of micro ceramic composite layer thickness,and the concentration of HCl solution can make crystal growth for granular,clavate and flocculent..（2）Through testing the mechanical properties and thermal expansion properties,explore the preparation of process parameters on the properties of composite materials macroscopic effects,realize composite was prepared by using parameters to control the mechanical properties and thermal expansion properties.according to the experimental data,the maximum compressive stress,elastic restoring force and the coefficient of thermal expansion of the sample are related to the solution concentration of the ZrW₂O₈ precursor and the solution concentration of HCl.In terms of mechanics,negative poisson phenomenon appears under certain preparation parameters and compressive strain;In the step by step cyclic loading experiment,the maximum compressive stress that can be borne under 90%strain is 167.9kPa through parameter control,and the rebound degree under this strain is close to 100%,greatly enhancing the mechanical properties of the original material.in terms of thermal,the negative thermal expansion coefficient of composites can reach-15×10-6 K-1 in the temperature range of 300-375K,which is smaller than that of graphene aerogel and ZrW₂O₈.The materials with adjustable coefficient of thermal expansion were prepared successfully by controlling parameters,and the phenomena of negative thermal expansion,positive thermal expansion and zero thermal expansion could occur in a certain temperature range.（3）ANSYS software was used to establish a simplified model of 3d graphene-based nano-ceramic composite material,and the thermal expansion response simulation and data statistics were conducted.Through numerical simulation analysis,the effects of the thickness of ZrW₂O₈ layer coverage and the interaction forceγbetween graphene monolayer and ZrW₂O₈ on the composite were studied,proving the possibility of controlling the thermal expansion coefficient of nano-ceramic composites by controlling the thickness and distribution of ZrW₂O₈layer by the preparation parameters.It is also proved that at 375K,the thermal expansion of the structure will change from negative thermal expansion to positive thermal expansion under the influence of the values of various coefficients.