Preparation And Properties Of The Carbon And Graphite Materials Fabricated By Self-sintering Mesocarbon Microbeads

Mesocarbon microbeads(MCMBs)are an excellent precursor of carbon and graphite materials(CGM)with high-strength and high-density.Because MCMBs have good self-adhensive and self-sintering performance,MCMBs as raw materials can omit some processes in traditional preparation processes of CGM,such as adding binders,kneading,repeated dipping and so on.This greatly reduces the complexity of production process and shortens production period of CGM.In addition,MCMBs have also advantages of good thermal stability,high spherical degree,small average particle size and less content of volatile,which results in the fact that the bending strength and compactness of CGM from MCMBs are superior to thoes of the traditional CGM.The marketable MCMBs,whose ?-resin content is less than 1wt%,are used as the raw materials in this paper.This paper have studied on the effects of granulation of kneading,average particle size of MCMBs,molding methods,molding pressure,carbonization heating rate,heat treatment temperature and other factors on the formability of MCMBs,sintering properties of green bodies,the compactness,microstructure and bending strength of CGM;though liquid phase dispersion method,wet ball milling method and solution method,SiC whiskers(SiCw),carbon nanotubes(CNTs),short carbon fibers(Cf),polyacrylonitrile preoxidized fiber(PCf)and Polycarbosilane(PCS)were respectively doped into MCMBs,researching the influence of the doping methods,the doping materials and the doping content on the morphology and properties of composite.This paper investigated the preparation process and properties of CGM fabricated by self-sintering MCMBs.The results indicated that MCMBs were hardly molded into compact green blocks by one-step uniaxial compaction.Although kneading method inproved the formability of MCMBs and the successful sintering property of green bodies,the uneven distribution of long cracks and large pores occurr in the interior of CGM.These cracks and pores obviously reduced the bending strength of CGM.When MCMBs were molded into integral green bodies by one-step cold isotropic pressing,these bodies were sintered into carbon material with bulk density of 1.82g/cm3,bending strength of 75.4MPa and open porosity of 10.8vol% after being carbonized at 1200?.Because the compactness of green bodies fabricated by MCMBs was obviously enhanced by two-step cold isotropic pressing,the carbon blocks formed by two-step cold isotropic pressing had higher bulk density of 1.84g/cm3,higher bending strength of 81.7MPa and lower open porosity of 3.14vol% than those of the carbon materials fabricated by one-step cold isotropic pressing after being carbonized at 1200?.Then,the graphite material prepared had bulk density of 1.92g/cm3,blending strength of 58.8MPa and open porosity of 4.29vol% after being graphitized at 2700?.The powders with the average particle size of about 5?m prepared from broken MCMBs were used to form green bodies by two-step cold isotropic pressing.These green bodies were carbonnized into carbon blocks with open porosity of 0.57vol% at 1200?.Finaly the graphite with bulk density of 1.92g/cm3,open porosity of 1.61vol% and flexural strength of 76.1MPa were obtained after being graphitized at 2700?.The preparation process and properties of doped CGM have been studied.The results revealed that mixing liquid phase dispersion method and wet ball milling method greatly improved the dispersal uniformity of the doping materials by liquid phase dispersion method.But wet ball milling method could break the spherical morphology of MCMBs severely,which descreased the yield of product after carbonation;The pore size of CGM doped by CNTs was small and the distribution of pores was very uniform,but the agglomeration of CNTs was very evident.When the doping content of CNTs was 2~5wt%,the bulk density of graphite materials at 2700? was decreased,and the bending strength and resistivity were enhanced with the doping content increased.The distribution of SiCw was more uniform than that of CNTs,but the chemical compatibility between SiCw and basic materials was bad,which led to easier occurance of pores along the suface of SiCw.The bulk density of CGM doped by SiCw increased at first then decreased with the increase of the content of SiCw.The Cf was more evenly distributed than CNTs and SiCw.The longer the length of Cf was,the more serious the crisscrossed phenomenon of Cf,which resulted in reducing the density and bending strength of sample.The green bodies doped by PCf were easier successfully sintered than those doped by Cf.The bulk densiy of decreased and the resistivity enhanced with the increase of the content of PCf.Doping CNTs,SiCw,Cf and so on into MCMBs impedes the self-sintering densification process of MCMBs,weakening the sintering properties and bending strength of CGM.