N220 Nanocarbon Black Containing Low Carbon MgO-C Refractory

Abstract

In iron and steel industries, MgO–C refractories are widely used in basic oxygen furnaces, electric arc furnaces and steel ladles due to their excellent corrosion resistance, thermal shock resistance, and other excellent hot properties. Conventionally magnesia carbon refractories contain about 8-20 wt% of carbon. Carbon in the magnesia- carbon refractories imparts advantages like non-wetting properties, high thermal conductivity, low thermal expansion, and low elastic of modulus, high thermal shock resistances and other superior properties.

But the use of carbon is also associated with disadvantages like oxidation, low fracture strength, high heat loss and higher carbon pick-up in steel. So, the tendency to use of high carbon content in the composition is stopped and researchers are developing MgO-C refractory having low carbon content without compromising the beneficial properties. Nano carbon, having finer particle sizes, can mix and distribute within the entire matrix uniformly even at a lower concentration and can result in improved mechanical, thermo mechanical, corrosion and other refractory properties.

Such a developmental research is planned in the present work to reduce the total carbon content in MgO-C refractory by using nano carbon, replacing partially the conventionally used graphite as carbon source. The nano carbon black was varied from 0 to 3wt% with an increment of 0.5 wt% in the MgO-C refractory compositions in combination with varying graphite content from 1wt% to 5wt%. All the compositions were processed through conventional MgO-C refractory manufacturing technique .The processed compositions were evaluated for various refractory properties namely densification, strength, oxidation, hot strength, penetration depth (corrosion) and were also compared against the conventional 16 wt% graphite containing batch prepared by using the similar raw materials processed under exactly similar conditions. Optimized amount for nano carbon and graphite content in the MgO-C composition has been evaluated and in the optimized composition, different types of metal powder anti oxidants (Al, Si and Mg) along with boron carbide were incorporated to identify the suitable anti-oxidant for such composition. The formation of in situ ceramic phases in the matrix was studied through microstructure and phase analysis and these compositions were also evaluated for various refractory related properties. The corrosion study against converter slag was also carried out at microscopic level for the batches (conventional and low carbon batch) containing different antioxidant metal powders. The optimized batch from nano carbon, graphite content and antioxidant type was further evaluated for thermal shock resistance, distribution of matrix phase and carbon by microstructural study, porosimetry study and also compared against the conventional only 16 wt% graphite containing composition. Batch composition containing 1 wt% nano carbon and 3 wt% graphite as carbon source with Al metal powder antioxidant was found to be the optimized one and showed improved properties compared to the conventional composition.

Uniform distribution of finer nano carbon black particles in the matrix phase fills the tiny void spaces between coarse, medium and fine particles of magnesia in a better way, thus enhancing the compaction of the composition resulting in improved densification, strength and other properties. However, greater extent of nano carbon content in the composition showed negative effect as the excess nano carbon particles could not enter in the voids, thus increased the bulk volume of the composition causing deterioration in the properties.