Hydration of coked MgO-C-Al refractories

摘要

Magnesia-carbon bricks collected from steel plants kept in open atmosphere were found to crack and disintegrate on prolonged exposure. To understand the mechanism of this behaviour, MgO-C-Al and Al-C samples were prepared, coked, and kept in open atmosphere. The samples crumbled to dust after few days. XRD showed the reduction of phases such as Al_4C_3, Al_4O_4C, Al_2O_3, and Al caused the disintegration with formation of amorphous phases. SEM showed the presence of hexagonal stack-like structures which converte to dust-like phases which EPMA identified as combination of aluminium and oxygen without the presence of carbon. Thermodynamic stability analysis for Al-O-C-H quaternary and Al-O-H ternary phase diagrams was done to explain the mechanism of hydration and consequent disintegration of coked MgO-C-Al bricks as well as Al-C samples on exposure to moist atmosphere at ambient temperature. On hydration, phases present in the coked samples convert to A1(OH)_3 which causes the disintegration.