Study On The Densification Process And The Mechanism Of High Density Graphite

High density graphite materials were prepared by dipping and roasting repeatedly with petroleum coke body and soft pitch as raw material in this research. With the help of thermal analysis(TG-DSC), Fourier transform infrared spectroscopy(FTIR), scanning electron microscope(SEM), X-ray diffraction(XRD) to analyze and compare the influencing factors in densification process. Meanwhile, this paper studies the internal mechanism which effects products’structure in the process.Experiment results show that petroleum coke heated under the Nitrogen protection atmosphere can effectively enhance the amount of coke. The body volume increased slightly was arised from binder softening and thermolysis before200℃. Between200℃to600℃, petroleum coke started to a lot of complex decomposition reactions, and the volumetric shrinkage reached a maximum. After600℃, the composition of the green coke turn into coke, and the volume basically unchanged. In addition, the baking heat curve was drow up based on the changing trend of petroleum coke thermal performance(TG-DSC) and its volumetric shrinkage with testing temperature.The analyses of FTIR and elementary on standard of baked show that the percentage content of carbon element increased, while hydrogen、oxygenium and sulfur reduced; the-C=O and-OH radicals and so on made a reduction, but-C≡C-H radicals appeared a great. Consequently, it was inferred that the simple carbon layers of baked had been basically established. From the view of macroscopic, green body bulk decreased and strength increased, however, plentiful micropores and fissures formed because of exhaust gas so that green body density decreased with porosity raised.The efficiency of impregnation is effected by impregnating properties and process parameters by analysising the principle of dipping, and the latter often influences the former. This paper took advantage of orthogonal design experiment to determine the key parameters-keeping Nitrogen pressure1.5MPa and impregnation temperature200℃for60min, and those experiment results show that the abilities which influence impregnation efficiency are as follows:temperature、pressure、 pressure holding time.The TG-DSC curve of soft pitch shows that its thermal performance is similar to the petroleum coke, so the repeatedly baking heat curve likes the first. But the difference between them is that the repeatedly baking heat curve heating speed faster and the highest temperature lower. After repeatedly roasting and dipping, the samples’ tightness and mechanical strength gradually raised, but with the increasing of processing times, the increasing degree of densification becomes more and more little. The results indicate that the best process is the4th roasting and3rd dipping.According to the mechanism of graphitization process, the graphitization curve was drow up, and the highest temperature set as2400℃. Also, the2400℃has been proved to be effective by thermodynamics of gibbs function. With the aid of such means as the scanning electron microscope and energy spectrum analysis、FTRI, found out that the structure and element content of graphitized have been changed obviously:the percentage content of carbon element further increased, also the sulphur element and other impurities were exhausted cleanly thus samples got purification; the surface of sample became more densifying, and the particles more refined, porosities were also reduced; In addition, the benzene rings and-C≡C-bonds increased obviously. Consequently, the microstructure of bodies from2-D random to3-D ordered griphite structures.Tests indicate that the mechanical strength and density of graphitized samples become larger as the increasing of processing times, such as the4th roasting and3rd dipping sample, its bulk density goes to1.72g/cm3, bending strength is19MPa and resistivity only13μΩ·m. Compared with roasted samples that the graphitized which resistivity subtracted60%, the true density increased more than5%and the linear expansion reduced33%. However, the bending strength and hardness show a somewhat lower. Furthermore, this paper by means of X-ray diffraction to get the samples’ graphitization degree, and precisely analyzes the relationship between graphitization degree, the linear expansion and the true density.