China's Refractories

As core and foundational materials for high-temperature processes in industries such as iron and steel, nonferrous metals, cement, glass, ceramics, chemicals, machinery, electric power, and national defense, refractories are directly pivotal to the operational stability and technological innovation of these sectors. However, the industry currently confronts multiple challenges, including constraints on raw material resources, bottlenecks in process technology, and a lag in intelligent transformation. To break through this development impasse from a scientific and technological innovation perspective, it is proposed to focus on diversified market demands, fully leverage the advantageous properties of raw mineral resources, accelerate integration and transformation through the “Artificial Intelligence + Refractories” model, and strengthen the development of original innovation capabilities. Through theoretical research and practical exploration, preliminary laboratory-scale results have been achieved, providing a new pathway and reference for the high-quality development of the refractory industry.

This study addresses the challenge of directly determining the elastic modulus of complex shaped ceramic products—such as gas turbine combustor tiles—using conventional standardized methods, which are limited by specimen geometry. A rapid, non-destructive testing method based on the impulse excitation technique (IET) and a shape factor coefficient was proposed. Three types of shaped ceramic tiles were selected. The elastic modulus of standard rectangular specimens obtained by destructive sampling was used as the reference value, and the shape factor coefficient for each tile type was calibrated by combining the mass and fundamental frequency of the whole tile. Using this coefficient, the elastic modulus of whole tiles was calculated solely from non-destructively measured mass and frequency. The results show that the deviation between the elastic modulus derived from the proposed method and that from destructive testing is less than 5%, confirming the accuracy and reliability of the approach. The method overcomes the shape restrictions inherent in traditional testing, offering a fast, non-destructive solution suitable for onsite quality assessment and process control during the production of shaped ceramic components.

To improve the performance of low-carbon magnesia carbon refractories, specimens were prepared using fused magnesia with particle sizes of 3-1, ≤ 1, and ≤ 0.074 mm, flake graphite with a particle size of ≤ 0.15 mm as the main raw materials, phenolic resin as the binder, and adding alumina micropowder with mass percentages of 1%, 3%, 5%, 7%, and 9%, respectively. The obtained green specimens were then cured at 200 °C for 24 h and heat-treated at 950 °C or 1 550 °C for 3 h. The effects of the alumina micropowder addition on the properties (including the apparent porosity, bulk density, cold compressive strength, cold modulus of rupture, hot modulus of rupture, and thermal shock resistance) as well as on the phase composition and microstructure of the low-carbon magnesia carbon specimens were investigated. The results show that the physical properties of the specimens are improved as the alumina micropowder addition increases, mainly due to the in-situ reaction between magnesia and alumina to form spinel, which enhances the bonding of the matrix and thus strengthens the overall bonding of the specimens. After the heat treatment at 1 550 °C, the bulk density, cold compressive strength, and cold modulus of rupture of the specimens first increase and then decrease with the increase of the alumina micropowder addition, reaching the optimal values when the addition is 7%. Both the linear change rate and volume change rate of the specimens increase with the increasing alumina micropowder addition.

Improving the green mechanical strength and thermal shock resistance of silica sol-bonded corundum castables is of great significance for promoting their large-scale application. Silica sol-bonded corundum castables were prepared using brown corundum, dense corundum powder, α-Al₂O₃ micropowder and SiO₂ micropowder as the main raw materials, and silica sol as the binder. The effects of different additions of chopped glass fibers (0, 0.2%, 0.4%, 0.6%, 0.8% and 1%, by mass) on the properties of the castables were studied. The results show that with the increase of the fiber addition, the cold modulus of rupture, cold compressive strength and hot modulus of rupture of the samples first increase and then decrease. After drying at 110 °C, the sample containing 0.4% fibers has the cold modulus of rupture of 9.1 MPa and cold compressive strength of 27.4 MPa, increasing by 80.4% and 41.2%, respectively, compared with the one without fiber addition. This is because the fibers bonded with the silica sol-gel interface to form a stressed skeleton, strengthening the bonding between the matrix and the aggregates. When subjected to external stress, the fibers can effectively share the load and prevent crack propagation, thus increasing the strength. In addition, the sample with 0.4% fibers has the highest cold modulus of rupture before and after thermal shock, and its strength retention ratio increases by 16.1% compared to the sample without fibers. Overall, the sample with 0.4% fibers exhibits the best comprehensive performance.

The recycling of waste activated carbon is of great significance in environmental protection. Porous mullite ceramics were prepared by impregnating the mullite precursor with activated carbon, adding a pore-forming agent, and adopting aluminum sulfate octahydrate, ammonia and silica micropowder as raw materials, waste activated carbon after heat treatment as the pore-forming agent, and sodium polyacrylate (PAAS) as the dispersant. The effects of the activated carbon additions (1.5%, 3.0%, 5.2%, and 7.8%, by mass) and PAAS additions (1%, 2%, and 3%, extra adding, by mass) on the physical properties, phase composition and microstructure of the porous ceramics were studied. The results show that: (1) as a pore-forming agent, activated carbon promotes the formation of pores inside the samples, while the apparent porosity of the samples increases significantly with the increasing activated carbon addition; when the activated carbon addition is 7.8%, the apparent porosity of the sample is 65.7%, the cold compressive strength is 4.62 MPa, the peak pore size is around 3.5 μm, and the pore size distribution is uniform; (2) appropriate PAAS helps to improve the dispersion of activated carbon in the samples and the comprehensive performance of the porous mullite ceramics; when the PAAS addition is 2%, the apparent porosity of the sample is 71.8%, the cold compressive strength is 5.53 MPa, the peak pore size is around 3 μm, and the pore size distribution is optimized; however, excessive PAAS increases the liquid phase in the system, resulting in over sintering of mullite and a decrease in the porosity.

To develop specific lining materials for rare earth steel nozzles, LaAlO₃ powder was first synthesized by high-temperature solid-phase synthesis at 1 400 °C for 3 h using La₂O₃ and Al₂O₃ powders as raw materials. Then BN, AlN, Si₃N₄ and TiN powders were pressed into φ 30 mm× 7 mm substrate samples under 120 MPa with PVA as the binder. Equal amounts of La₂O₃ and LaAlO₃ powders were placed on their surfaces, reacting at 1 550 °C for 3 h in different atmospheres (reducing and argon conditions). The interfacial reactions of the four nitride (BN, Si₃N₄, AlN, and TiN) substrate samples with La₂O₃ and LaAlO₃ in different atmospheres were studied, respectively. The results show that in reducing and argon atmospheres, the intensity order of the reactions between the four nitrides and La₂O₃ is Si₃N₄>BN>AlN>TiN. In the reducing atmosphere, the reaction intensity order of the four nitrides with LaAlO₃ is Si₃N₄>AlN≈TiN>BN. However, in the argon atmosphere, the order is Si₃N₄>BN>AlN≈TiN. TiN has good structural stability in both reducing and argon atmospheres, and shows weak reactivity with La₂O₃ and LaAlO₃. It is a relatively good anti-clogging lining material for rare earth steel nozzles.

Adding magnesite flotation concentrate powder in the production of fused magnesia has become an important method for reducing costs and improving the yield. However, the extensive use of concentrate powder also reduces the quality of fused magnesia raw materials, which is a major cause of the reduced slag corrosion resistance and service life of magnesia-carbon refractories. The effects of concentrate powder additions (0, 30%, 60%, and 90%, by mass) on the chemical composition, phase composition, microstructure, bulk density, and apparent porosity of the produced 97-grade fused magnesia were investigated. The results show that as the concentrate powder addition increases, the bulk density first increases and then decreases, while the apparent porosity first decreases and then increases. The crystal size of the fused magnesia increases, and the pores at the grain boundaries become larger. The CaO/SiO₂ molar ratio (C/S ratio) in the fused magnesia increases from 1.17 to 4.17. The bonding phases between the fused magnesia grains change from low-melting-point phases such as CMS (CaMgSiO₄) and C₃MS₂ (3CaO·MgO· 2SiO₂) to high-melting-point phases like C₂S (2CaO·SiO₂), C₃S (3CaO·SiO₂), and CaO, which is beneficial for improving the high-temperature performance of the fused magnesia. However, during production, the volume effects resulting from the polymorphic transformation of dicalcium silicate (C₂S) and the low-temperature decomposition of tricalcium silicate (C₃S) create significant voids around the fused magnesia grains. These voids can provide pathways for slag corrosion in subsequent magnesia-carbon products, which is likely the primary reason for the decline in the slag corrosion resistance and service life of carbon-containing refractories made from this type of fused magnesia.