Effect of Raw Material and Preparation Process on the Structure and Performances of Isostatic Pressing Graphite
|Keywords||Isostatic Graphite Modified Asphalt Impregnation and Baking times Forming Pressure Structure and Performance|
The last century60’s，Isostatic graphite was developed as the high performanceengineering materials. Isostatic graphite has the advantages of high temperatureresistance, corrosion resistance, good electrical and thermal conductivity, lowcoefficient of thermal expansion properties, so it is widely used in the nuclearindustry the high temperature gas cooled reactor, EDM electrode graphite crucible,semiconductor, metal continuous casting crystallizer, rocket nozzles a nd otherindustrial fields. Isostatic graphite is mainly composed of aggregate and the binder, Itwas prepared by molding, baking, impregnation and graphitization process. In thebaking process, binder pyrolysis emitted volatile and left a hole in the body, thereby itreduced the volume density of material, affecting the structure and properties of thematerials. In order to improve the physical and mechanical properties of isostaticgraphite material, it should go about from raw material selection and prep aration ofits effect on the structure and properties of materials, and take multiple baking andimpregnation process to improve the bulk density of materials, so as to strengthen thephysical and mechanical properties of materials.In this paper, isostatic graphite was prepared from the filler of petroleum coke,pitch coke and natural graphite and the binder of modified pitch by kneading, molding,baking, impregnation and graphitization, the structure of it was characterized by usingenvironmental scanning electron microscopy (SEM), metallurgical microscope andX-ray diffraction.Effect of filler type, binder type, asphalt content and formingpressure on the structure and properties of isostatic graphite was research.The experimental results show the volume density of isostatic graphite increaseswith the number of immersion, while the resistivity of it decreases with the dippingtimes; After second dipping and third baking, the volume density and resistivity ofisostatic graphite prepared by three kinds of different filler materials makes a littledifference; Isostatic graphite prepared by petroleum coke own high mechanicalproperties: compressive strength of72.0MPa and flexural strength of39.9MPa. Aftersoaking and graphitization treatment, the volume density, compressive strength,flexural strength and hardness of isostatic graphite prepared by different adhesiveincreased with the number of immersion. After second dipping and third baking andgraphitization, isostatic graphite prepared by modified asphalt B has compressive strength of51.9MPa, shore hardness of29.6, flexural strength of21.9M Pa, theresistivity of11.2μΩ M. With the increasing of forming pressure, the bulk density,compressive strength, flexural strength and resistivity of isostatic graphite firstincrease and then decrease. Isostatic graphite has volume density of1.74g/cm3,compressive strength of45MPa, flexural strength of19.8MPa, and theresistivity of11.2μΩ M. The shore hardness and compressive strength of isostaticgraphite prepared by different asphalt content increases with increasing immersionand baking times. With the increaseing of asphalt content, the binder content of31%preparation of isostatic graphite had the best mechanical properties. After thirdimpregnation and graphitization, the resistivity of isostatic graphite prepared bydifferent binder content decreases rapidly. The asphalt content of31%preparation ofisostatic graphite resistivity only is8.8μ Ω m.