China's Refractories

To solve the problems of short service life and poor adaptability of RH snorkels under the refining conditions of complex steel grades, a series of calcium hexaaluminate-based castables were prepared using calcium hexaaluminate particles as the aggregates, calcium hexaaluminate fine powder, corundum fine powder, spinel fine powder and reactive α-Al₂O₃ micropowder as the matrix, and pure calcium aluminate cement as the binder. The results show that calcium hexaaluminate (CA₆) aggregates can not only bond with Al₂O₃ but also with MgO-Al₂O₃ (MA) spinel materials. Three kinds of calcium hexaaluminate-based castables developed in this work all exhibit enhanced cold and hot strength with the rising temperature. It is found that the CA₆ castable with MA spinel matrix has the best corrosion resistance to RH refining slag, desulfurization slag and desulfurizer, together with excellent thermal shock resistance. This material is widely adaptable to RH refining conditions. The service life of the developed calcium hexaaluminate-based castable applied to the RH desulfurization snorkels exceeds the average life of the current corundum-spinel materials, indicating that the new material can meet the severe requirements of refining working conditions. It provides a new material option for RH snorkels used in the treatment of complex steel grades.

Zirconia-based refractories, characterized by high refractoriness, good corrosion resistance, and low colorability, are therefore widely used in critical areas of glass furnaces. In view of the severe corrosion of refractories by fluorine-containing opal glass, four refractory materials with different zirconia contents—ZR95, Z80, Z60, and AZS41 were selected and their corrosion resistance using the static crucible method at 1 600 °C for 48 h was investigated in this work. The corrosion behavior was evaluated by combining the dimensional changes at the liquid line and the SEM/EDS interfacial analysis. The results show that the four materials all exhibit low corrosion degrees by opal glass, with ZR95 and Z80 retaining more intact interfaces and demonstrating superior corrosion resistance. After the corrosion test, Z80 displays a slight dimension increase at the liquid line, which may be related to the formation of an adherent surface layer or a protective zirconia-rich layer. These findings can provide a reference for the selection of refractories for furnaces processing fluorine-containing opal glass.

Ceramic fibers play a crucial role in thermal insulation and heat preservation in high-temperature industrial fields. However, a complex system of temperature indicators, including maximum service temperature, classification temperature, and long-term service temperature, often confuses users during material selection and application. In this work, the intrinsic definitions and interrelationships of temperature indicators for ceramic fibers from the perspectives of standard specifications, testing methods, and influencing factors were systematically analyzed. The effects of the chemical composition, microstructure, and service environment on the material properties were also investigated, providing professional guidance for scientific material selection and safe engineering design.

To enhance the resource utilization of magnesite tailings and reduce the production cost of magnesia-based refractories, porous MgO-Mg₂SiO₄-MgAl₂O₄ aggregates were synthesized in-situ using magnesite tailings and coal gangue powder as raw materials, firing at 1 300 °C for 4 h. The effects of the coal gangue powder additions (0, 10%, 20%, 30%, and 40%, by mass) on the phase composition, microstructure, bulk density, apparent porosity, cold crushing strength, and thermal shock resistance of the specimens were investigated. The results show that: (1) with the increase of the coal gangue powder addition, the linear shrinkage of the specimens first decreases and then increases, the volume shrinkage and the apparent porosity decrease, the bulk density and the cold crushing strength increase, and the crushing strength retention ratio first increases and then declines; (2) when the coal gangue powder addition is 30%, the specimen primarily consists of the crystalline phases of MgO, Mg₂SiO₄, and MgAl₂O₄, showing the optimal comprehensive performance: a linear shrinkage of 12.7%, a volume shrinkage of 30.5%, an apparent porosity of 43.4%, a bulk density of 1.84 g·cm^-3, a cold crushing strength of 56.0 MPa, and a crushing strength retention ratio of 83.3% after 3 thermal shocks.

The material selection, refractory products design, and engineering application for rotary kilns in hazardous waste disposal in China were summarized in this paper. Unified specifications for rotary kilns regarding brick shapes, masonry proportioning, refractory material selection, and the core equipment of incinerators were established. The group standard T/CMCA 40022-2021 was compiled to provide standardized, replicable technical solutions for hazardous waste disposal enterprises of different regions and scales. Extensive field verification shows that standardized design and material selection effectively lower the manufacturing, replacement, and maintenance costs of rotary kiln refractory bricks, greatly improving the operation stability of hazardous waste incineration rotary kilns and prolonging the service life of refractory bricks.

To address the challenges associated with the agglomeration of magnesia and its poor dispersion stability in sol systems, the effects of the sodium pyrophosphate additions (0-2.5 mass%), suspension pH (7.9-11.5), and ultrasonic dispersion time (0-20 min) on the dispersity and stability of the magnesia powder were investigated. Subsequently, SiO₂-coated magnesia powders were prepared using sodium silicate as the raw material through the sol-gel method. The influence of the coating time (1-9 h), coating temperature (55-95 °C), suspension pH value (7.5-11.3), and sodium silicate solution dosage (1%-5%) on the surface properties of the powders was studied. The results indicate that within certain ranges (the sodium pyrophosphate addition <1.5%, the pH <11.5, and the ultrasonic dispersion time >5 min), the dispersity of the magnesia powders improves with the above parameter values increasing; however, when the sodium pyrophosphate addition exceeds 1.5% and the ultrasonic dispersion time is shorter than 5 min, the dispersity gradually deteriorates. After being coated with SiO₂, as the coating time prolongs, the coating temperature increases from 55-65 °C, or the pH rises, the dispersity of the magnesia powders first increases and then decreases. Generally, under the following conditions: coating time of 7 h, coating temperature of 65 °C, pH of 10.5, and sodium silicate solution dosage of 5%, the magnesia powder exhibits the optimal dispersity, with d₅₀=45.2 μm, d₉₀=70.5 μm, and the minimum specific surface area of 792 m²·kg^-1.

To utilize coal gangue solid waste as a resource, a slurry was prepared by mixing coal gangue powder (d₅₀=75 μm), CaCO₃ powder (d₅₀=75 μm), and α-Al₂O₃ powder (d₅₀=5 μm) at a mass ratio of 6 : 3 : 1, with 35 mass% distilled water added. Then, 2 mass% composite foaming agent NS-Ⅲ was added to the slurry to form a foamed slurry. The foamed slurry was poured into a 100 mm×100 mm×50 mm mold. The demolded green bodies were first dried at 100 °C for 24 h and then fired at different temperatures (1 200, 1 250, 1 300, and 1 350 °C) for 3 h to fabricate anorthite insulating refractories. The effects of the firing temperature on the phase evolution, microstructure and properties were investigated. The results show that (1) with the increasing firing temperature, the diffraction peak intensity of anorthite and mullite gradually increases, the anorthite crystals increase and gradually develop from short columnar to lamellar; the crystal bonding gradually enhances; the bulk density, linear shrinkage and thermal conductivity of the samples decrease firstly and then increase, while the apparent porosity shows an opposite trend, and the cold compressive strength gradually rises; (2) when the firing temperature is 1 300 °C, the sample exhibits the optimal overall performance, with the bulk density of 0. 48 g·cm^-3, apparent porosity of 84.3%, cold compressive strength of 1.80 MPa, and thermal conductivity of 0.139 W·m^-1·K^-1 at 1 000 °C, and the anorthite crystals in the sample show lamellar morphology and bond closely, which makes the sample suitable for long-term service at high temperatures.

To improve the service life of high-temperature melting furnaces for treating low- and intermediate-level radioactive waste, high-temperature melt was prepared by simulating the typical waste composition, and the microstructural changes and corrosion of alumina-chrome refractory materials before and after exposure to the high-temperature melt were analyzed using FactSage thermodynamic calculations combined with static crucible slag resistance tests, along with SEM and EDS characterization. The results indicate that the corrosion of alumina-chrome refractories by the high-temperature melt mainly involves the dissolution of corundum, zirconia, alumina-chromia solid solution, and chromia crystals, as well as melt penetration into the brick. As the chromia content increases, the corrosion resistance improves while the penetration resistance decreases. The nepheline formation accelerates the melting of Al₂O₃ in the bricks. The dissolution of various components in alumina-chrome bricks follows the order Al₂O₃>ZrO₂>Cr₂O₃. Na₂O and SiO₂ in the high-temperature melt exhibit the strongest penetration.