Preparation Technology And Performances Of Carbon Foams By Slurry Stirring And Foaming

In this thesis,graphite powder was used as the main raw materials.Based on the preparation of graphite slurry with good dispersibility and fluidity,bubbles were introduced into the slurry by mechanical stirring,then carbon foams were prepared by freeze-drying or foam-gelcasting method.The bulk density,porosity,thermal conductivity and compressive strength of carbon foams were characterized.The thermal properties and its influencing factors of carbon foams were emphatically analyzed.The carbon foams prepared in this thesis have the advantages of low density,high porosity,low expansion coefficient,adjustable thermal conductivity,and have a broad application in the aerospace thermal control materials.The freeze-drying method is suitable for graphite-gelatin system and gelatin system,using graphite powder,gelatin and pure gelatin as raw materials respectively.After foaming by mechanical stirring,freeze-drying,carbonization and graphitization,the carbon foams were prepared.In the graphite-gelatin system,the volume foaming rate of the slurry is 2.07?4.89,open porosity of the samples is 91.86?70.36%,bulk density is in the range of 0.16?0.48 g/cm~3,compressive strength varies from 0.37 to2.47 MPa,the degree of graphitization is 77.91?79.07%,and thermal conductivity is1.38?20.69 W/(m·K).The change laws of its properties are:as the gelatin content increased or the foaming agent concentration decreased,the volume foaming rate,porosity and pore size of the samples gradually decreased,while compressive strength,thermal conductivity and bulk density increased,and the degree of graphitization was unchanged.In the gelatin system,the volume foaming rate of the slurry is 1.2?2.15,open porosity of the samples is 52.30?62.80%,bulk density is in the range of 0.56?0.66g/cm~3,compressive strength varies from 20.56 to 30.95 MPa,the degree of graphitization is 19.05?20.93%,and thermal conductivity is 2.54?3.47 W/(m·K).The change laws of its properties are:as the gelatin content increased,the volume foaming rate,open porosity of the samples increased firstly and then decreased,while compressive strength,thermal conductivity and bulk density of the samples decreased firstly and then increased,and the degree of graphitization was unchanged.Due to the low degree of graphitization,the thermal conductivity of the samples prepared from the gelatin system is lower than that of the samples prepared from the graphite-gelatin system.The foam-gelcasting method is suitable for graphite-acrylamide system.Acrylamide monomer and crosslinking agent were added into the graphite slurry.The slurry was mechanically stirred and formed by polymerizing gel of organic monomer and the carbon foams were obtained after microwave drying.The bulk density of the samples is 0.36 g/cm~3,the porosity is 78.68%,the compressive strength is 0.35 MPa,and the thermal conductivity is 0.1850 W/(m·K).The research results show that the foam-gelcasting method has the advantages of simple process,high efficiency,low cost,and the prepared materials are high porosity and processability.However,the strength and thermal conductivity of the carbon foams prepared by foam-gelcasting method are low.The materials prepared by freeze-drying method have the advantages of high strength and high thermal conductivity,but it requires certain equipment conditions.The carbonization treatment mainly changes the composition and microstructure of the materials,while the graphitization treatment changes the crystal structure of the materials,thereby improving the thermal conductivity of the carbon foams.