Construction Of High Thermal Conductive Network In Electrically Calcined Anthracite Based Carbon Blocks And Their Properties For Blast Furnace

Carbon blocks are the key refractories in the hearth and bottom for blast furnace,whose service life determines the campaign life of blast furnace.With the development of intensified iron-making technology,the working conditions of hearth and bottom become more and more severe,which demands carbon blocks possessing high thermal conductivity.With respect to improving the thermal conductivity,substances with high thermal conductivity are generally introduced into carbon blocks,such as replacing traditional electrically calcined anthracite（ECA）with artificial graphite.Besides,Si together with Al or SiO₂ powder was also added into carbon blocks to improve the thermal conductivity by in-situ forming lots of AlN,Al₃C₄ and SiC ceramic phases at high temperature.However,ECA based carbon blocks are the mainstream product for blast furnace,adding lots of artificial graphite will lead to the high cost of carbon blocks.Therefore,how to further improve the thermal conductivity of ECA based carbon blocks is an urgent task for now.Therefore,in this thesis,ECA was firstly treated through activation technology to improving its graphitization degree and reactivity,which accelerated the reaction of forming SiC whiskers and thus improved the thermal conductivity of carbon blocks.Then,catalyst was introduced into carbon blocks via ECA aggregate and resin binder,which could catalyze pyrolysis carbon of resin forming carbon nanotubes（CNTs）at high temperature,optimizing the interface bonding between aggregate and matrix and decreasing the interface thermal resistance,thus improving the thermal conductivity of carbon blocks.Subsequently,reactive carbon sources were incorporated into carbon blocks to accelerate the formation of SiC whiskers in the matrix,which constructed high thermal conductive network to improve the thermal conductivity.Additionally,ECA aggregate was treated by vacuum alumina slurry infiltration technology,the density of aggregate was enhanced due to the alumina ceramic phase filling the pores.Or the pores and cracks in aggregate were reduced by decreasing the critical particle size of aggregate,and the area of ceramic phase bonding carbon aggregate was correspondingly increased to construct matrix high thermal conductive network,thus improving the thermal conductivity of carbon blocks.Finally,regression modelling of processing parameters and thermal conductivity of carbon blocks was conducted with the aid of Support Vector Machine（SVM）,which ascertained the influence degree of processing parameter on the thermal conductivity and provided the theoretical guidance for fabricating carbon blocks with high thermal conductivity.Based on the work above,the main conclusions can be made as follows:1.The content of graphite and reactivity of ECA were improved by thermally oxidation and microwave activation technology,which accelerated the reaction of ECA and Si containing gaseous phases to form SiC whiskers at high temperature.The addition of above-mentioned activated ECA in carbon blocks accelerated the formation of SiC whiskers and optimized the interface characteristic between ECA aggregate and matrix,thus improving the thermal conductivity remarkably.2.CNTs could be catalytically formed from pyrolysis carbon of resin binder in carbon blocks with addition of Ni containing catalyst,which reacted with Si containing gaseous phases and transformed into SiC whiskers under high temperature.Compared with the CNTs prepared with CVD method,CNTs could be in-situ catalytically formed from pyrolysis carbon of resin by directly dispersing Ni containing catalyst on the surface of ECA aggregate or into resin binder.Some CNTs reacted with Si containing gaseous phases and transformed into SiC whiskers,which constructed excellent interface structure of ECA aggregate-CNTs/SiC whiskers-matrix,and thus enhancing the mechanical property and thermal conductivity of carbon blocks.3.Graphite-SiC whiskers high thermal conductive network was constructed by introducing carbon sources with high reactivity in carbon blocks.The thermally oxidized graphite flake,ultrafine graphite and pitch were added into carbon blocks,which accelerated the formation of SiC whiskers in the matrix and formed graphite-SiC whiskers high thermal conductive network,thus improving the thermal conductivity and mechanical properties of carbon blocks.4.Thermal conductivity as well as hot metal erosion resistance of carbon blocks was enhanced by applying vacuum alumina slurry infiltration technology and decreasing the critical particle size of aggregate,which was attributed to the improvement of density of ECA aggregate.ECA were made by calcining the anthracites at high temperature,the pores and cracks could be formed in ECA due to the evaporation of organic substances.After treating ECA with vacuum alumina slurry infiltration technology,alumina could fill the pores and cracks and densify the ECA aggregate.Besides,the pores and cracks could be also reduced by decreasing the critical particle size of aggregate,which contributed to improving the thermal conductivity,cold compressive strength and hot metal erosion resistance of carbon blocks.5.The relationship model of relevant factors about influencing thermal conductivity were constructed and their contribution to thermal conductivity was revealed.Then,thermal conductivity of carbon blocks was predicted by SVM.The regression fitting formula of thermal conductivity and relevant factors based on SVM revealed that as for the improvement of thermal conductivity,thermally oxidized graphite flake played the most important role while ECA aggregate had the minimal impact.Based on the fitting formula,the thermal conductivity of carbon blocks prepared by artificial graphite and thermally oxidized graphite flake was almost precisely predicted.