Formation of hollow MgO-rich spinel whiskers in low carbon MgO–C refractories with Al additives

MgO–C refractories with different carbon contents have been developed to meet the requirement of steel-making technologies. Actually, the carbon content in the refractories will affect their microstructure. In the present work, the phase compositions and microstructure of low carbon MgO–C refractories (1 wt% graphite) were investigated in comparison with those of 10 wt% and 20 wt% graphite, respectively. The results showed that Al4C3 whiskers and MgAl2O4 particles formed for all the specimens fired at 1000 °C. With the temperature up to 1400 °C, more MgAl2O4 particles were detected in the matrix and AlN whiskers occurred locally for high carbon MgO–C specimens (10 wt% and 20 wt% graphite). However, the hollow MgO-rich spinel whiskers began to form locally at 1200 °C and grew dramatically at 1400 °C in low carbon MgO–C refractories, whose growth mechanism was dominated by the capillary transportation from liquid Al at these temperatures.