Synthesis of CaO·2MgO·8Al2O3 (CM2A8) and its slag resistance mechanism

CM2A8 is a solid solution of MA and CA6. As a component in the ternary phase diagram of CaO-Al2O3-MgO, it was not reported in detail. So in this work, analytically pure CaO, MgO and Al2O3 were adopted as starting materials and batched stoimotrically according to CM2A8. The raw materials were ground, mixed, shaped and reaction-sintered at different temperatures (1550 °C, 1650 °C, 1700 °C, and 1750 °C) to synthesize CM2A8. The synthesized specimens were analyzed by XRD, SEM, and TEM and the corrosion mechanism against LF slag was also researched. The results show that high-purity CM2A8 can be synthesized by reaction sintering at 1750 °C. During synthesis, granular MA and flake CA6 form and grow together; at 1650 °C, they solid-solve together to form C2M2A14. As the temperature rises, solid solution reaction goes on, which results in the disappearance of CA6, C2M2A14, and MA in succession and forms high-purity CM2A8 growing towards hexagonal column crystals. In the high temperature reaction between CM2A8 and steel slag, Ca2+ in the slag reacts with CM2A8 to form CA2, damaging the structure of CM2A8 and releasing excessive Mg2+ and Al3+ which move towards the molten slag. As the reaction between Ca2+ and CM2A8 proceeds, a dense CA2 coating forms on the surface of CM2A8. The slag viscosity increases as well because of the entrance of Mg2+ and Al3+. Thus, the formation of the CA2 coating and the enhancement of the slag viscosity restrain the penetration and corrosion of slag towards CM2A8.