Figure 11: Backscatter electron micrographs of the protective slag coating 4: Conclusion and Outlook
Laboratory corrosion trials revealed that slag penetration into MgO-C bricks is reduced when the bricks are doped with a small amount of CMA- additive. Unlike in the CMA-free brick, the carbon bond between the MgO grains remains strong and protected by a slag coating. In steel ladle trials a protective slag coating on the hot surface and a joint sealing effect was observed. Both effects seem to contribute to the improved service life when the CMA-additive is employed in the carbon bonded bricks. It will be further investigated if thermomechanical effects and/or thermochemical mechanisms are at the source of the joints protection-effect. Since the in-situ formed protective layer improves the resistance against carbon oxidation it allows to reduce the amount of expensive anti-oxidants like Al- and Si-metal. Further industrial trials with the CMA-additive are running to evaluate its efficiency as well in other carbon-containing and carbon-free refractory bricks and monolithics.
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Figure 12: MgO-C bricks with 2.5% Antioxidants after 47 heats (LF47) (left) and MgO-C bricks with 5% CMA and 1.5% antioxidants after 55 heats (LF51) in metal zone of a 70 t steel ladle
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