Optimization Of Matrix Composition Of The Low Carbon MgO-C Refractories

Magnesia-carbon refractories maintain excellent high temperature performances of basicrefractories,and radically change some inherent defects,such as poor spalling resistanceperformance as well as easy slag corrosion.So magnesia-carbon refractories are widely used ininner lining or slag line of converter,electric aic furnace and ladle.With the development ofsteel-making new technology,some problems are found in the application of traditionalmagnesia-carbon refractories,like great heat loss, low/ultra-low carbon steel-making and largegraphite resources consumption.Therefore, the application of low carbon magnesia-carbonrefractories becomes an inevitable trend.Some excellent performances of magnesia-carbonrefractories have been affected as the carbon content decreasing, such as the decreasing ofthermal shock stability and resistance to penetration of slag.So it is of vital importance tooptimize the matrix composition of low carbon magnesia-carbon refractories.This workmainly covers three aspects, the choice of carbon, modification of the binder as well as theintroduction of combined antioxidant. Conclusions are drawn as follows.The specimens of low carbon magnesia-carbon refractories with single or combinedcarbon of different kinds were prepared. And volume density, apparent porosity, roomtemperature compressive strength and thermal conductivity of the specimens were examined.The result proves that superfine flake graphite as single carbon can be well dispersed in matrixof magnesia-carbon refractories. Then a continuous uniform carbon structure forms aftercarbonization, which makes magnesia-carbon refractories show excellent performances.However, superfine flake graphite and expanded graphite as combined carbon can fill thepores of magnesia-carbon refractories, which makes magnesia-carbon refractories presentgood room temperature performances and compact microstructure. Low carbonmagnesia-carbon refractories with0.35%graphene oxide added can show excellentperformance as well as uniform matrix structure. Additionaly, SiC whisker can form fromcarbon and Si mixture with nickel nitrate used as catalyst treated in Ar atmosphere at1000℃or1100℃.XRD, SEM and EDS are used to characterize the carbonized modified bonder. Theresults shows carbon nanotubes/carbon nanofibers can form from Ni-modified resin aftercarbonization at900℃in Ar atmosphere. The temperature is favorable to their growth. Whenthe treatment temperature increases to1000℃, carbon nanotubes/carbon nanofibers becomelonger. SiC whiskers can form from silicon and nickel nitrate compound modified pitch aftertreated in Ar atmosphere at1000℃. SiC whiskers gradually become straight and thick with theincrease of carbonization temperature. When the processing temperature increase to1400℃,Si in the modified pitch is completely converted into SiC. When nickel-modified pitch andnickel-modified resin is used as the binder of low carbon magnesia-carbon refractories, carbonnanotubes/carbon nanofibers form in situ of the matrix after the specimens treated at1200℃in a reducing atmosphere.The matrix of low carbon magnisa-carbon refractories with combined antioxidant wasinvestigated.According to a certain ratio, magnesia powder, superfine flake graphite,aluminum powder and titanium dioxide are uniformly mixed.The result shows that TiN andMgAl₂O₄form from the mixture respectively treated at1000℃and1300℃in a reducingatmosphere. When the processing temperature increase to1500℃, the solid solution Ti（C,N） forms from TiN and TiC. With the introduction of3%Al and1%TiO₂combined agent, theoxidation resistance of low carbon magnesia-carbon refractory is significantly improved,while the formation of spinel in situ reinforces the strength of the low carbon magnesia-carbonrefractories. In addition, the introduction of Al and TiO₂combined agent can avoid theformation of Al₄C₃and prevent the bricks from cracks of hydration.