Development of Environment Friendly New Generation MgO-C Brick Using Nano Carbon

Abstract

MgO-C refractory is widely used in steel making application, mainly in steel ladles , LD converters, electric arc furnaces and also in secondary steel making. It is a basic refractory with superior slag /metal corrosion and penetration resistance and excellent thermal shock properties at high temperatures. In steel ladle applications a carbon content of 8-20 wt% is used. The function of the C is to fill the porous structure, improve the slag / metal corrosion andpenetration resistance due to its non-wetting character and enhancement of thermal shock resistance due to its high thermal conductivity and low thermal expansion characteristics. Again formation of a nascent dense layer of MgO at the working surface of MgO-C brick, due to oxidation of Mg (produced on reaction between MgO and C) restricts the penetration of slag / metal components and thereby further improves the penetration and corrosion resistance. But C suffers from poor oxidation resistance and may oxidise to form CO and CO2 resulting in a porous structure with poor strength and corrosion resistance. Prevention of carbon oxidation is done by using antioxidants, which reacts with incoming oxygen, gets oxidised and protects carbon, thus retaining the brick structure and properties. These antioxidants play a vital role in the MgO-C brick performance.
Again use of high amount of carbon in the refractory has many disadvantages too. Higher the carbon means higher thermal conductivity that results more amount of heat los through the refractory. Again higher the heat loss, higher will be the shell temperature of the steel vessel, resulting in higher chances of deformation of shell and reduction of ladle life. Also higher carbon increases the chances of carbon pick up in steel, which is in contradiction to steel making, a decarburization process. Further,more use of carbon in refractory will increase the generation of CO and CO2 gases and thus may become a concern for global environment. Hence, globally the researchers and scientists are considering and working for reduction in the total amount of carbon in MgO-C brick without compromising with the final characteristics. The present work is also aimed to reduce the carbon content in the MgO-C refractory brick using nano carbon, replacing the conventionally used graphite. Nano carbon content is varied from 0.3wt% to 1.5wt% and graphite was used upto 5wt%.
MgO-C bricks are prepared using conventional manufacturing technique with both pitch and resin binder. Pressing is done at 2 ton /cm2and curing is done at 200oC for 12 h. The products are
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characterised in terms of bulk density, apparent porosity and cold crushing strength for both cured and coked (1000oC for 5h) conditions. Also modulus of elasticity (MOE) hot modulus of rupture (H MOR) at 1400oC, oxidation resistance at 1450oC for 5h and corrosion resistance are tested for the cured samples. All the properties are compared with conventional brick (containing 10 wt% of graphite) prepared under similar manufacturing conditions. Oxidation resistance of the nano carbon containing compositions are found to be much better than that of the conventional ones. All the batches show nearly comparable values of hot strength. 0.9wt% nano carbon containing composition is found to have optimum properties and this batch was further studied with variation in antioxidant quality and quantity. B4C, Al are used as antioxidant and their amount is varied in the range of 0.5 -1 wt%. B4C containing compositions are found to have improved oxidation resistance, strength and corrosion resistance.