On the in-situ aluminothermic reduction of manganese oxides in continuous galvanizing baths

The in-situ aluminothermic reduction of manganese oxide (MnO) by dissolved Al in the continuous galvanizing bath was investigated. Thick (approximately 410 nm) MnO films were grown on a 5.1 wt.% Mn steel by annealing at 770 degrees C for 600 s using a conventional -30 degrees C dew point N-2-5% H-2 process atmosphere. The MnO films formed were then reacted with a 0.20 wt.% dissolved Al bath at 460 degrees C for reaction times ranging from 1.2 s to 21.0 s. Significant reductions of MnO film thickness were observed for all reaction times, with the reduction in MnO being a linear function of reaction time for the reaction times explored. It was determined that an Al2O3 reaction product was present at the coating-oxide interface with significant concentrations of Mn being detected in the metallic coating adjacent to the reaction front. It was also determined that the MnO layer was not altered chemically for any of the reaction times explored. From these results, it was concluded that the previously proposed in-situ aluminothermic reduction of MnO by the bath dissolved Al proceeds by a dissolution mechanism. It was further concluded that that the aluminothermic reduction of MnO in the continuous galvanizing bath has been validated. (C) 2012 Elsevier B.V. All rights reserved.