Wettability Of Natural Microcrystalline Graphite And Its Application In Isotropic Graphite Preparation

Due to its excellent properties,isotropic graphite has important applications in different engineering fields,including high temperature gas-cooled reactor,metallurgical casting,semiconductor preparation,and so on.Natural microcrystalline graphite(MG)is formed by micro-crystallites with randomly orientations,leading to a near-isotropic structure of MG particles.This kind of structure makes MG a natural raw material of isotropic graphitepreparation.In this thesis,purified MG was selected as filler material to prepare isotropic graphite,and the wetting behavior of MG with pitch was studied by measuring the contact angle of pitch.Then the behavior changes of graphite green bodies during carbonization process were discussed.Finally,the properties and structures of MG-based isotropic graphite were evaluated.Wettability of MG particles with pitch was characterized using a pitch drop spreading test.The wetting results show that pitch drop can completely wet MG substrate,and the excellent wetting behavior is closely related to the specific crystalline structure and surface morphology of MG.Firstly,(002)edge planes on MG surface were beneficial for pitch to interact with filler particles.Secondly,the relatively high roughness of MG particles would help to enhance its wettability.Thirdly,high crystallization of MG showed a negative result in pitch wetting test.The wetting tests have clearly shown that this negative result caused by high graphitization can be compensated by its crystallite orientations and surface roughness.The wetting behavior of MG during kneading can help form homogeneous paste and improve the interfacial strength between filler and pitch.The carbon yield of pitch can be improved during co-carbonization because of the adding of MG filler.As the temperature increasing,the volume of different green bodies experienced process of expanding before shrinking,and the density accordingly would decrease and then increase.Due to the poor interfacial energy,the fracture of different samples occurred at the interface of filler and binder.MG-based graphite showed excellent results in density,degree of graphitization,flexural strength and isotropy ratio over coke-based samples.The particle size of MG had no obvious effect on density,degree of graphitization and isotropy ratio,but decreasing particle size will increase the strength of graphite artifacts.Using MG filler with particle size of 9.6 ?m as filler material,graphite artifact with density of 1.75g·cm-3,strength of 24.56 MPa and isotropy ratio of 1.04 can be obtained,confirming the application of MG in isotropic graphite preparation.