Degradation of MgO refractory in CaO-SiO2-MgO-FeO x and CaO-SiO2-Al2O3-MgO-FeO x slags under forced convection

Abstract

Experiments based on exposure of MgO to slags under forced convection flow conditions allowed the identification of different degradation mechanisms and the assessment of the role of Al 2 O 3 in the degradation process. Slag with no alumina present resulted in direct dissolution. Samples immersed in alumina containing slag underwent indirect dissolution, with a spinel forming at the MgO-slag interface. At 1530 °C, the spinel was not effective in reducing the corrosion rate, as the scattered spinel grains were easily removed from the MgO surface. At 1500 °C, the loss of MgO was reduced due to the formation of a more cohesive spinel layer. Mechanical erosion then appears to play a greater role. Strength of the bond between the spinel and underlying MgO needs to be considered in strategies to reduce degradation of MgO refractories.

Kinetics of Spinel Formation and Growth during Dissolution of MgO in CaO-Al2O3-SiO2 Slag

“…This is in agreement with observations made during dissolution of polycrystalline MgO. [6,9] There is a large volume change associated with the transformation from MgO to MgAl 2 O 4 . The lattice parameter of the spinel (0.808 nm) [16] is almost double that of MgO (0.421 nm), [17] resulting in significant mismatch and strain at the interface, which could lead to fracture and detachment of the spinel crystals.…”

“…[1][2][3][4][5][6] Evidence from quenched samples has suggested that the spinel forms at the liquid/solid interface, but then often becomes detached from the solid unless anchored by protrusions on the solid MgO surface. Therefore, this layer can be easily removed by forced liquid flow.…”

Effect of changing slag composition on spinel inclusion dissolution

“…[1][2][3][4] The formation of these spinel layers can be a process positive, slowing the refractory corrosion rate if they remain adhered to the refractory surface. Unfortunately, if the spinel oxide layer does not remain attached to the refractory, then it can become a source of inclusions for the steel.…”

In-situ observation of dynamic interfacial phenomena between CaO-(SiO2 or Al2O3) slag and Fe-11%Cr alloy near the MgO-6%C refractory at 1823 K

“…From a thermodynamic perspective, the Marangoni convection at the slag-metal-refractory interface was less of a dominant factor determining the corrosion rate of the MgO-C refractory than the large solubility limit and the mass transfer in the slag phase both of which played a far more dominant role. In order to better understand the reaction kinetics between the MgO-C refractory and the molten slag, further experiments (such as the rotating finger experiments [22]) should be carried out.…”