As an important raw material of magnesia based refractories, the dissolution of the fused magnesia in the CaO-Al₂O₃-SiO₂ slags for refining a low density and high strength steel is an important factor affecting the service life of furnace lining and the quality of steel. In this paper, the dissolution behavior of fused magnesia in the slag at 1 600 ℃ was investigated by a high-temperature laser confocal microscopy system. The effects of the shape and mass of magnesia particles and the mass fraction ratio of CaO to SiO₂(C/S) on the dissolution behavior were investigated. The results show that the shape of fused magnesia particles has little effect on its dissolution rate. The dissolution rate decreases linearly with the increase of mass, and it decreases firstly and then increases with the increase of C/S ratio. The dissolution curve of magnesia particles is affected by the mass, and the n values of the dissolution model can correspond to 1/2, 2/3 and 3/5, respectively. This work provides a guidance for understanding the slag corrosion behavior of magnesia based refractories, improving the quality and optimizing the performance of magnesia based refractories.

With the development of hydrogen metallurgy and hydrogen-based shaft furnace, the corresponding refractories for critical parts have higher requirements. Understanding the service environment characteristic and implementing targeted design for the performance are thus particularly important for refractories. In this paper, the temperature, pressure and gas phase concentration distribution for interior and wall surface in reduction domain of hydrogen-based shaft furnace were simulated by a software named Ansys. Also, the thermodynamic stability of typical components of traditional refractory during the process was calculated by FactSage. The results show that the high-temperature and high-pressure service area is concentrated near the gas inlet, while H₂O is concentrated in the top and bottom areas of the furnace. Increasing the temperature of inlet gas has a certain effect on the temperature field, but has little effect on the pressure field and gas phase composition. Among the typical components of conventional refractory, Al₂O₃, ZrO₂, magnesium aluminum spinel, calcium-hexaluminate and TiO₂ exhibit a thermodynamic stability, which can be used as potential refractory components of furnace walls. AlN or TiC can be used as additive materials to improve the relevant properties of these refractories. In addition, some impurity components as SiO₂, MgO, CaO, Cr₂O₃, Fe₂O₃, SiC, Si₃N₄, B₄C and BN can be eliminated. This study can provide a theoretical basis and methodological support for the service environment simulation and material component selection of refractory for a hydrogen-based shaft furnace.

Crucible refractories are very important for the quality of titanium alloy smelting. In order to develop novel crucible material with high performance, in this work, Y₂O₃-Al₂O₃-MgO-CaO composite refractories were prepared with commercial yttrium oxide and Al₂O₃-MgO-CaO powders (AMC) as raw materials, and the effects of sintering temperature (i.e., 1 500 ℃, 1 600 ℃) and AMC contents (i.e., 0, 25%, 50%, 75% and 100%, in mass fraction) on the phase compositions, sintering properties (i.e., linear shrinkage, volumetric shrinkage, apparent porosity, and bulk density), compressive strength at room temperature, thermal shock resistance and microstructures of as-prepared refractories were investigated. The results show that the most properties of the composites are improved, compared with Y₂O₃ and AMC. The performance becomes better as the sintering temperature increases. Moreover, the linear shrinkage, volumetric shrinkage, bulk density and compressive strength at room temperature of the composites increase with the increase of AMC contents. At the AMC content of 75%, the composite sintered at 1 500 ℃ for 3 h has the optimum comprehensive performance (i.e., the apparent porosity of 4.37%, the compressive strength at room temperature of 274.99 MPa, the residual strength after three water-cooling and thermal shocks of 161.60 MPa, and the residual strength ratio of 58.78%).

The application of graphite flakes in refractory castables was inhibited by their poor water-wettability, and carbides modified graphite was considered as the best way to solve this problem. Aimed to solve the high cost, difficulty in scalable fabrication, and unclear synthesis mechanism in the preparation process of carbide-modified graphite, a core-shell SiC@graphite powder was fabricated in air by a modified molten salt shielding technique in this work. Influence of encapsulation method on the phase composition and microstructure of as-obtained SiC@C powders was investigated. The results show that SiC@C powders can be fabricated via modified molten salt shielding method. The as-prepared SiC@C powders possess better water-wettability, dispersibility and oxidation resistance. The microstructural characteristic of SiC@C powders is indicated a core-shell structure, SiC layer is formed on graphite flake. The template-growth mechanism is dominant in molten salt synthesis process, i.e., a small amount of Si is dissolved in the molten salt, diffused onto the graphite surfaces via a molten salt medium, and then reacted to form in-situ SiC coating layer on graphite flake, which is controlled due to the external diffusion of element Si.

Periclase-hercynite refractories are used in the firing zone of the cement rotary kiln, which is inextricably linked to their reaction behavior with cement clinker at high temperatures. In this paper, the corrosion behavior of magnesia aggregate and hercynite aggregate as well as periclase-hercynite refractory with cement clinker at high temperatures was investigated by scanning electron microscopy, X-ray diffraction, and Factsage simulation, respectively. The results show that magnesia particles have a superior corrosion-resistance to cement clinker, and the reaction of hercynite with cement clinker produces massive high-temperature liquid phase, which is gradually corroded. The periclase phase and hercynite particles have a synergistic effect on resisting the cement clinker corrosion in periclase-hercynite bricks at high temperatures. The periclase matrix as a major crystalline phase reacts with cement to generate a high melting point phase, forming a skeletal structure in the grain boundary phase, improving the grain boundary phase's high-temperature viscosity, and promoting the combination of clinker and refractory. Also, ion exchange between hercynite and magnesia promotes the combination of hercynite and matrix, while inhibiting the formation of low melting point feldspar phases at high temperatures. Furthermore, the high-temperature stability of hercynite is improved, which benefits the kiln coating stability when using the refractory in the firing zone.

Magnesium silicate hydrate (MgO-SiO₂-H₂O M-S-H) is a main bonding phase for microsilica bonded magnesium-castables used for tundish. Its content determines the mechanical properties after demolding. In this paper, M-S-H was synthesized with Na₂SiO₃·9H₂O and MgCl₂·6H₂O as raw materials. The effect of M-S-H at different calcination parameters was investigated by X-ray diffraction, scanning electron microscopy, specific surface area measurement, nuclear magnetic resonance, and thermogravimetry-differential scanning calorimetry. Moreover, the synthesized M-S-H with microsilica powder (1%) was introduced into the magnesia-based castables to evaluate their influences on the properties. The results show that M-S-H has a memory effect when the calcination temperature is below 400 ℃. Increasing the calcination time can facilitate the insertion of interlayer hydroxyl groups in M-S-H gels and contribute to the formation of a lamellar structure with a higher structure stability. A certain amount of pre-synthesized M-S-H and a small amount of silica powder can assure the castable with a good workability and a sufficient early bonding strength. The reduced silica can suppress the formation of large sized defects due to the volume shrinkage of matrix, in the interface of aggregates and matrix, thus improving the mechanical properties of castables. This work provides a support for the development of magnesia-based castables with a low silica content.

Cement rotary kilns using refractories require excellent refractoriness, thermal shock stability and corrosion resistance due to the cyclic rotation and feeding-discharging of cement clinker. In this paper, a kind of magnesia-alumina spinel refractory containing coating structured aggregates were prepared by wrapping spinel fines on the surface of magnesia aggregates. The fracture behavior and corrosion resistance of prepared refractories were characterized by three-point bending test combined with digital image correlation, acoustic emission technique, and static slag resistance method. The results indicate that by changing the distribution of spinel to make coating structure aggregates, the alumina content is effectively reduced while a more uniform and extensive distribution of spinel phase is achieved. Compared with the merchant magnesia-alumina spinel refractory (10% Al₂O₃) with pre-synthetic spinel aggregates, the magnesia-alumina spinel refractory (5% Al₂O₃) with spinel coating aggregates has the improved mechanical strength and corrosion resistance, and maintains the thermal shock resistance.

Bauxite ores usually contain some iron and titanium oxides, which are difficult to remove simultaneously with conventional beneficiation processes. The oxides of iron and titanium will form low melting point phases during the preparation of mullite by sintering with bauxite, resulting in a reduction of the high-temperature properties of mullite. This review represented the solid solution behavior of iron oxides and titanium oxides in mullite based on the open spatial structure of mullite and its ability to accommodate different metal ions at different temperatures and atmospheres. The solubility of TiO₂ in mullite is 1.36%-4.10% at 1 400-1 700 ℃. Fe₂O₃ of 10%-12% can make a solid solution in mullite microstructure at 1 300 ℃. Ti³⁺ and Fe²⁺ are poorly solidified in mullite. Moreover, the formation of solid solutions of iron and titanium with mullite provides a limited enhancement of mullite properties. In addition, the efficient use of mullite containing iron and titanium was also discussed.

The melting of refractory in slag and the penetration of slag into refractory are the main reasons for the damage of refractory. These two aspects are related to the wettability between slag and refractory at a high temperature, and the wettability can be evaluated by the surface tension, adhesion work and spreading coefficient of slag on the refractory surface. The wettability of slag and refractory can be inhibited by changing the composition and roughness of the refractory, thus resulting in the improved service life of the refractory. This review represented the factors affecting the high-temperature wettability between refractories and slag based on the aspects of slag composition, refractory composition and surface microstructure effect. In addition, the future research direction in this field was also prospected.

In large-scale blast furnaces, the use of a proper refractory material for taphole as the most severe working area of blast furnaces has attracted much attention. This review introduced the main properties of taphole clay as a refractory material for blast furnace taphole, i.e., its plasticity, corrosion resistance and sintering properties, and summarized recent relevant work on taphole clay for aggregate, matrix and binder. In addition, the future development of taphole clay was also prospected.