China's Refractories

This paper reviews the current development status and achievements of China's refractory industry, summarizing the significant progress made by China's refractory industry over the past 40 years in energy conservation, environmental protection, green and low-carbon development, and intelligent manufacturing. It analyzes the challenges and difficulties faced by China's refractory industry currently, focusing on how the current adjustment cycle in China's steel industry provides new opportunities for China's refractory sector. China's refractory industry must adhere to the path of innovation-driven, intelligent manufacturing, green and low-carbon. We should seek and seize new opportunities for transformation and upgrading, continuously optimize the industrial structure, enhance product and service quality, and carefully balance the domestic and international markets. This approach aims to form a new capacity management mechanism that includes market competition and constraints from both energy consumption and carbon emission, with government supervision and industry self-discipline.

Al₄SiC₄ was prepared using Al powder, silicon carbide powder, and graphite as raw materials, and silicon as the additive by microwave sintering. Effects of silicon additions (0, 5%, 10% and 15%, by mass) on the phase composition, microstructure, apparent porosity and bulk density of the Al₄SiC₄ sample prepared with different aluminum additions (20%, 25%, by mass) were researched. Then the developed Al₄SiC₄ samples were applied to MgO-C bricks to investigate the effect on the oxidation resistance and mechanical properties of the MgO-C bricks. The results show that Al₄SiC₄ can be synthesized at lower temperatures using the microwave sintering method. The sample with 20% aluminum addition has a lower Al₄SiC₄ content than the one with 25% aluminum. When the silicon addition is 10% and the aluminum addition is 25%, the sample appears needle-like system, the porosity is only 28.69%, and the sample is dense. The developed Al₄SiC₄ was added into MgO-C bricks as the antioxidant, which greatly increased the oxidation resistance and the mechanical properties of the MgO-C bricks.

To maintain the volume stability of lightweight magnesia-silica castables during heating, lightweight spherical forsterite aggregates (8-5, 5-3, 3-1 and 1-0 mm), pre-synthesized forsterite fine powder (≤0.074 and ≤0.044 mm), natural silica powder (≤0.074 mm), middle grade magnesia fine powder (≤0.074 and ≤0.044 mm) and silica fume were used as the raw materials to prepare lightweight magnesia-silica castables, and the magnesia fine powder and natural silica powder were gradually replaced by pre-synthesized forsterite fine powder (10%, 20%, 30% and 40%, by mass). The properties of the castables were tested and the microstructure was analyzed. The influence of the pre-synthesized forsterite fine powder addition on their properties was researched. The results show that: with the increase of the pre-synthesized forsterite fine powder addition in the matrix, the workability of the castables is almost the same. After being heated at 1 450 ℃ for 3 h, the bulk density of the castables increases, the apparent porosity decreases, the permanent linear change changes from expansion to shrinkage, the cold strengths increase firstly and then decrease, and the thermal conductivity at different temperatures increases. Generally, the optimal pre-synthesized forsterite fine powder addition is 20%.

Ceramics with proper pore sizes and geometry are critical to many applications, so that lots of efforts have been made to achieve the goal. Direct ink writing (DIW), an additive manufacturing technique, is cost-effective and accessible. It is interesting to study the ability to control the pore size and geometry by the DIW technique. In this study, alumina ceramics were prepared with special focus on the pore configuration and the performance of printed samples was tested. The porous structures with different pore sizes (minimum pore size of 200 μm) and different shapes (honeycomb, lattice and triangle) were printed. The printed structures shrunk uniformly and maintained the original geometry after firing, they did not show any visible defects or deformations, and the microstructure was uniform and dense. It was found the honeycomb structures exhibited superior mechanical strength at the same porosity compared to lattice and triangle structures, which reached 55 MPa with a porosity of 70%. The high strength with the high porosity was attributed to the highly controlled microstructure, i.e., uniform pore sizes, pore shapes and interconnectivity.

To provide a material with excellent comprehensive properties for the glass kiln melting pools, zirconia powder and alumina powder were fully mixed according to the ratio of m(ZrO₂) : m(Al₂O₃)=4 : 1 and fused in an arc furnace. The obtained fused zirconia-corundum eutectic material was processed into different particle sizes, batched according to a certain particle size distribution and mixed evenly. After pressure molding and firing at 1 750 °C, new zirconia-based composites were prepared. The phase composition and microstructure of the composites were analyzed. The molten glass corrosion resistance of the composites was compared with that of zirconia corundum bricks 33^# and 41^#. The results show that the new zirconia-based composites have a dense structure, high chemical purity without low melting point components, and good thermal shock resistance. Compared with zirconia corundum bricks 33^# and 41^#, after being corroded by high temperature molten glass, the new composites have no corrosion cavities, needle-like pores, defects or liquid phase infiltration, and no reaction with molten glass, showing good corrosion resistance to molten glass.

Two kinds of pure calcium aluminate cement (CAC) prepared by the sintering method and the electric melting method, respectively were analyzed in terms of the particle size, XRD patterns and hydration characteristics; and their effects on the hydration heat and construction performance of the cement-based castables were discussed. It is found that (1) the electric fused CAC contains 50.67% CA and 44.89% CA₂, while the sintered CAC contains 74.57% CA and 22.97% CA₂; in addition, compared to the sintered CAC, the electric fused CAC contains more C₃A, C₁₂A₇, and a small amount of amorphous phase; (2) the electric fused CAC (d₅₀ of 7.93 μm) has much smaller particle size than the sintered CAC (d₅₀ of 12.51 μm); (3) in the early stage of hydration, the exothermic peak of the electric fused CAC appears earlier and the heat flow rate is higher than that of the sintered CAC; the dormant period of the sintered CAC is relatively short and the main exothermic peak appears earlier than that of the electric fused CAC; (4) for cement-based castables, there is no obvious exothermic peak in the early hydration stage, but the temperature of the castables slightly increases; among them, the initial hydration temperature of the electric fused CAC-based castable is higher; and the main exothermic peak of the sintered CAC-based castable appears later than that of the electric fused CAC-based castable; (5) the exothermic heating on-site occurrs earlier, which is related to the higher environmental temperature (about 30 °C); the on-site electric fused CAC-based castable begins to show more cracks during the exothermic peak stage.

To expand the application of multi-layer graphene in water-based systems, modified multi-layer graphene was prepared by vacuum impregnation with silica sol and carbon-embedded heat treatment at 300, 500 or 700 °C for 3 h. The phase composition, microstructure and wettability of the modified multi-layer graphene heat treated at different temperatures were studied. The results show that the water wettability of the modified multi-layer graphene is improved after vacuum impregnation with silica sol and carbon-embedded heat treatment; the optimum heat treatment temperature is 300 °C, and the modified multi-layer graphene has the water wetting angle of 64.7°.