To improve the quality and efficiency of the nickel metal melting process, the performance of oxygen-rich top-blown melting furnaces must be considered, particularly the furnace lining material used in the melt pool area. As a furnance lining, the refractory material is exposed to the mechanical and thermal stresses, and the corrosion of the refractories by the slag is an important cause of their failure. Investigating the corrosion resistance of refractories is thus a prerequisite to improve the service life of materials and ensure the product quality. Semi-rebonded magnesia-chrome bricks with a superior high-temperature performance is currently the first option for oxygen-rich top-blown furnace linings. However, the effect of Cr⁶⁺ after using magnesia-chrome bricks should not be ignored due to environmental protection requirements. The development of refractories with a superior high-temperature performance can replace the semi-rebonded magnesia-chrome bricks used directly in the oxygen-rich top-blown molten furnace bath, which is imperative. In this paper, different types of bricks (i.e., semi-rebonded magnesia-chrome bricks, high alumina bricks, and clay bricks) were used, and their phase compositions and microstructures were analyzed. In addition, the mechanism of high-temperature corrosion of nickel slag and refractories was also investigated via thermodynamic simulations, thus providing a theoretical reference for the design and manufacture of environmentally friendly furnace lining materials.

The corrosion resistances of semi-rebonded magnesia-chrome bricks (Beijing Yenai Jiye New Technology Co., China), high alumina bricks (Zhengzhou Rongsheng Kiln Refractories Co., China), and clay bricks (Zhengzhou Rongsheng Kiln Refractories Co., China) to nickel slag with the size of 325 mesh (Jinchuan Group Co., Ltd., China) from the top-blown furnaces were analyzed by a static crucible method. The crucible specimens used were cylindrical specimens with a diameter of φ50 mm×50 mm and holes with a diameter of φ 20 mm×20 mm in the center, which were drilled with a rock drilling and coring machine. The dried crucible was filled with 25 g of nickel slag powder and reacted at 1450 ℃ for 3, 7, and 11 h to obtain specimens after corrosion. The corroded specimens were then cut uniformly along the axial direction, and their cross-sections were analyzed. After fixing the corroded specimens with epoxy resin, the specimens were polished to obtain specimens for microstructure analysis.

The microstructures of the corroded specimens were determined by field-emission scanning electron microscopy in the back-scattered electron mode (FE-SEM, Gemini 500, ZEISS Co., Germany). The phase compositions of the corroded specimens were analyzed by X-ray diffraction (XRD; D/MAX 2000PC, Rigaku Co., Japan). The corrosion reaction was simulated by a software named Factsage (version 7.0) for thereaction, equilib, and viscosity modules of the thermodynamics simulation.

The semi-rebonded magnesia-chrome bricks, high alumina bricks, and clay bricks are exposed to nickel slag corrosion at high temperatures. The semi-rebonded magnesia-chrome bricks are found to be more resistant to nickel slag corrosion and penetration because of the formation of a spinel isolation layer at the interface between the slag and the refractory. The slag content in both the high alumina bricks and clay bricks during reaction with nickel slag corrosion is higher than that in the semi-rebonded magnesia-chrome bricks under the same conditions. Al₂O₃ in the clay bricks continuously dissolves in the slag due to the presence of more SiO₂ in the slag, resulting in a poor resistance of the clay brick to nickel slag corrosion. The viscosity of the slag gradually increases due to the grid structure formed by Si-O, weakening the penetration of the slag into the clay brick. Although high alumina bricks have some resistance to nickel slag corrosion, their resistance to nickel slag penetration is worse than that of clay bricks.

The spinel isolation layer formed during the corrosion reaction between the semi-rebonded magnesia-chrome bricks and nickel slag effectively blocked the penetration of slag into the interior of the material. High-alumina bricks could only form a corrosion isolation layer when corundum reached a saturation solubility in the slag. A corrosion isolation layer could not be formed during the corrosion reaction of the clay bricks. However, as mullite continued to dissolve in the slag, SiO₂ content in the molten slag increased and the network structure composed of Si-O enhanced the viscosity of the slag, thus weakening its ability to penetrate the interior of the clay bricks.