Atmosphere and carbon effects on microstructure and phase analysis of in situ spinel formation in MgO–C refractories matrix

The effects of carbon, air and reducing atmospheres on microstructure and phase evolution of in situ MgAl2O4 spinel (S) formation in the matrix of MgO–C refractories were investigated by X-ray diffraction powder analysis (XRD) and scanning electron microscopy (SEM)/energy-dispersive spectroscopy (EDS) techniques. The formation of spinel started under 1000 °C in both air and reducing atmospheres. The morphology of in situ spinel and its formation mechanism were however different and dependent upon the atmosphere. The solid-state reaction was clarified to be the dominant mechanism of spinel formation in oxide atmosphere, while the gas–solid reaction was found to play a vital role in reducing atmosphere. Reaction of MgO and C in reducing atmosphere led to the formation of Mg(g) which was found to be partially controlling the in situ spinel formation in the carbon containing samples fired in reducing environment. The results which were necessary are explained with emphasis on MgO–C refractories applications.