The Effect of Sodium Hexametaphosphate on the Physical and Mechanical Properties of Monolithic Refractories Prepared from the Wastes of Magnesia - Carbon Bricks

Magnesia–carbon (MgO–C) refractories are widely used in basic oxygen furnaces, electric arc furnaces and steel ladles. These refractories have excellent slag resistance and thermal shock resistance due to the good properties of carbon such as low wettability, high thermal conductivity and low thermal expansion. In this context, main problems are erosion of the refractories of slag line, carbon oxidation, chemical corrosion and mechanical wear of refractories by slag and need to repair and replace them with other refractories. In this study, the effect of using sodium hexametaphosphate(SHMP) as a bonding agent was investigated in the presece of water and spent magnesia-carbon refractory aggregates. For this purpose, different compounds composed of 0, 3 and 5 wt. % SHMP are prepared and some parameters such as bulk density, percent of apparent porosity (%AP) and cold crushing strenght (CCS) were measured at different temperatures (200, 500 and 1100 °C) and phase and microstructure studies were performed by XRD and SEM. Results indicated that using of 5% SHMP at different temperature, specially at low temperature causes some phosphate bonds with needle-shape morphology like MgP2O7, Mg3(PO4)2 and AlPO4 and improve physical and mechanical properties, so these monolithic refractories can be used for the cold repairing of ladles.