Research On Fabrication And Properties Of High-density And High-strength Graphite Materials Prepared From MCMBs Modified By Coal-tar Pitch

As a high quality precursor for preparing high-density and high-strength carbon/graphite materials, the theory of modification and preparation for mesophase microcbeads has beening researched widely in plant and laboratory, and has got a lot of results.Many research showed the MCMB containing 5%?9%? resin self-sintered very well and oriented randomly,which was suitable for preparing high-density and high-strength carbon/graphite materials.In current research, business MCMB which contains 7.68wt% volatile and 2.9wt%(3resin were adopted and self-sintered badly, according to solution-blending the MCMB were modified in this thsis,overcoming the problem of distributing nonuniformly because of less binder,then traditional iso-tropic molding was adopted to prepare bulk graphites, in orde to provide better guidance for making use of low volatile MCMBs (Mesophase microbeads) to prepare high-density and high-strength graphite.Firstly,thermal analysis and SEM were adopted to study the sinterability and impact of MCMBs modified by coal-tar pitch on the performance of graphite materials.The result showed that solution-blending could lay the pitch on the surface of MCMBs, there were still a little remnanat THF in the powder, in the process of carbonization, all the green bulks successively exhibit swelling and shrinkage,and the green bulks prepared from modified MCMBs exhibit swelling in a wider range until 600?, comparing with the non-modified green bulk swelling until 450?, shrinkage and weight loss rised dramatically between 600-1100?,and the electrical resistivity also decreased dramatically as the increase of degree of structural order,low hating rate was advised in this temperature range when baking to avoid cracking.Increasing the pitch contant properly can increase shrinkage in process of high-temperature hating,so that the density of graphites were increased.Secondly,the influence of MCMBs modified by different type and contant coal-tar pitch on the sinterability of MCMB powder and performance of graphite materials were studyed. The results demonstrate that coal tar pitch can coat,or in the form of super fine grains, the surface of the MCMB(D50=23?m) uniformly,a small number of pitch distributing between MCMBs in the form of big grains.By contrast,the MCMB modified by MS have the most rough surface,the area on the surface coated by pitch was also most. And the flexural strength of the materials increased corresponding to the sequence of high softing pitch(HS),modified pitch(MP) and middle softing pitch(MS), the values were 27.7MPa,42.7MPa and 56.9MPa respectively when pitch contant was 10wt% and molding pressure was 150MPa. If the pitch contant and molding pressure were increased properly,the flexural strength,density,hardness and electric conduction could also be improved.At last,the influence of solvent types and desolventizing temperature and time on the performance of graphites were studied.The result showed that the flexural strength and density of graphite prepared from MCMB solved by THF and modified by MP were 41.0MPa and 1.85g/cm3 respectively,when desolventizing temperature was 90?and desolventizing time was 12h.The performance of graphite prepared from MCMB solved by THF and modified by MP was superior to graphite prepared from MCMB solved by TOL and modified by MP.The volatization of TOL was delay until the temperature range after 300?,which was the most violent range of green bulk swelling and densifying, so the integration of MCMBs was hindered, so that the porosity of graphites was improved,at the same time the mechanical property and electric conduction decreased.