Microstructure and mechanical properties of MgO–C refractories containing expanded graphite

MgO–C refractories containing expanded graphite particles (EGs) and Al, Si additives were prepared. The EGs were prepared firstly by exfoliating commercial expandable graphite. Then, the composite powder containing EGs was obtained by mixing EGs and magnesia powder and incorporated into MgO–C refractories. The microstructure and mechanical properties of all the MgO–C refractories obtained were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), three-point bending and thermal shock tests. The results showed that EGs affected the microstructural evolution of MgO–C refractories. Much more interlocking aluminum carbides and nitride phases formed in the matrix of the specimen containing EGs because of their higher activity compared to flaky graphite. Also, EGs had a positive influence on the mechanical properties of MgO–C refractories. MgO–C specimens containing EGs had much higher cold modulus of rupture and better toughness compared to the specimens containing only flaky graphite; furthermore, the thermal shock resistance of MgO–C refractories was improved with the addition of EGs. It was suggested that EGs and in-situ formed ceramic phases in the matrix had a strengthening and toughening effect on MgO–C refractories.