Preparation,Structures And Properties Of Graphene Nanosheets/Carbon Foam Composites

Carbon foams are a new type of light weight porous carbon materials with unique microstructure and special performances,such as excellent adsorption performance,high porosity,large surface area,good thermal stability,and adjustable electrical conductivity,thermal conductivity,and therefore they have attracted increasing attention in many fields ranging from thermal management system,battery electrode,aeronautics,astronautics,catalyst support.However,the development and application of carbon foams are greatly restricted by their poor mechanical strength.An approach to solve this problem was to prepare carbon foam composites;nevertheless,it still confronted a series of challenges like difficult molding,high cost and complex manufacturing process.This research focused on preparation of graphene nanosheets(GNs)-reinforced carbon foam composites to improve the mechanical strength of carbon foams.In this paper,the GNs/cyanate ester(CE)resin mixtures were prepared using epoxy resin(EP)-modified bisphenol Acyanate ester resin as material and GNs as reinforcement.The preparation process involved ball-milling,prepolymerization,bubble removal,casting and curing.Pyrolysis behavior of the GNs/CE resin mixtures was studied.Results show that the pyrolysis behavior of modified CE resin is basically unchanged after the addition of GNs.The pyrolysis of the GNs/CE resin mixtures can be roughly divided into two stages and the maximum decomposition temperature remains around 424? and 440 ?.With the increasing of additive amount of GNs from 0 to 8 wt.%,the initial decomposition temperature and final decomposition temperature of the resulting mixture decrease initially and then increase.GNs/carbon foam composites were prepared by direct pyrolysis of the GNs/CE resin mixtures at ambient pressure.The effects of the additive amount of GNs on the mechanical properties,microstructures and thermophysical properties of the resulting GNs/carbon foam composites were investigated.The results show that the cells were mainly open and the surface of cell walls become rougher as the additive amount of GNs increases.With the the additive amount of GNs increases,it may remarkably improve the mechanical properties,electrical conductivity and thermal conductivity.When the GNs content is 6 wt.%,the bulk density,compressive strength,modulus,thermal conductivity and electrical conductivity of the composite reach the maximums of 0.38 g/cm3,7.11 MPa,115.90 MPa,16.38 S/cm and 1.227 W/m-K respectively.The influences of high-temperature treatment on the structures and properties of the GNs/carbon foam composites were investigated.Results show that the microcrystalline structure of the GNs/carbon foam composite is improved with increasing treatment temperature,and meanwhile its graphitization degree and the interfacial bonding between GNs and carbon-matrix increases.The bulk densities of composites with the same proportion first decrease and then increase with the increasing temperature,while the porosities show the opposite trend.Moreover,when increasing the final pyrolysis temperature from 900 ? to 1800 ?,the electrical conductivity and thermal conductivity of the carbon foam composite,prepared with a GNs content of 6 wt.%,increase from 16.35 to 92.81 S/cm and 1.227 to 1.914 W/m·K,respectively.The ultimate compressive strength of the carbon foam composite arrives at 7.36 MPa after the heat treatment at 1800?.