China's Refractories

The microstructure and phase composition of high-alumina, chromic oxide, and AZS/Cr refractories containing 30% and 60% (by mass) Cr₂O₃ after exposure to aluminaboronsilicate glasses and basalt melts depending on the type of melts and temperature have been studied. The mechanisms of refractory corrosion by the used melts and the factors contributing to the inhibition of corrosion development have been investigated by the method of petrographic analysis. On the basis of obtained results, the use of high-alumina, chromic oxide, and AZS/Cr refractories in the sections of glass furnace linings, experiencing the intensive impact of aluminaboronsilicate glasses and basalt melts, has been confirmed and scientifically substantiated.

This paper aims to improve the corrosion resistance of dispersive purging plugs. White fused corundum particles and fine powder, α-Al₂O₃ micropowder, Cr₂O₃ micropowder, Guangxi clay and zircon powder were used as the main raw materials. The mass ratio of white fused corundum particles and fine powder was fixed at 85 : 15, and 0, 1%, 2%, or 3% (by mass) of zircon fine powder was added to replace the same amount of white fused corundum fine powder. The corundum porous material was prepared by the particle stacking pore-forming method at 1 650 ℃ for 3 h. The effect of the zircon addition on the properties and microstructure of porous materials was investigated. The results show that: after adding zircon, the permeability of the porous material increases, the cold and hot strengths increase obviously, and the expansion rate after firing decreases. When the addition of zircon is 2%, the comprehensive performance of the specimen is optimal with the smallest linear change rate and the highest permeability.

Al₄SiC₄ was synthesized from Al powder, silicon carbide, and graphite by microwave sintering, and characterized by XRD and SEM. Then the synthesized material was added to the magnesia carbon refractory brick to study its effect on the oxidation resistance, apparent porosity, bulk density, elastic modulus, and modulus of rupture. It is found that Al₄SiC₄ can be synthesized by microwave sintering at 1 300 ℃ and the addition of Al₄SiC₄-containing material as an antioxidant can enhance the oxidation resistance of the magnesia carbon refractory brick.

To address the issues of reduced performance and shortened lifespan during the low-carbonizating process of Al₂O₃-C refractories, nano-crystalline ZrC modified graphite was prepared using Zr powder and flake graphite as raw materials, with NaCl and NaF mixed salt serving as the medium. The flake graphite was gradually replaced by ZrC modified graphite in the preparation of Al₂O₃-C refractories, and its impact on the material's structure and properties was investigated. The results indicate that, compared to samples with only flake graphite, the introduction of 1 mass% to 5 mass% nano-crystalline ZrC modified graphite can significantly enhance the mechanical performance of low-carbon Al₂O₃-C refractories. When 5 mass% ZrC modified graphite is added, the mechanical properties of the samples are optimal, with the cold modulus of rupture and elastic modulus reaching 22.5 MPa and 65.0 GPa, respectively.

To optimize their Al₂O₃-SiO₂ raw materials, anorthite based insulation refractories were prepared by the in-situ sintering process combined with the foaming method after sintering at 1 350 ℃ for 3 h, using green and pollution-free kaolin, kyanite, andalusite and sillimanite as Al₂O₃-SiO₂ raw materials, respectively, and industrial CaCO₃ as the CaO source. Effects of Al₂O₃-SiO₂ raw material types on the physical properties, phase composition and microstructure were investigated. The results are as follows. All samples prepared by different Al₂O₃-SiO₂ raw materials have hexagonal flake anorthite and a small amount of mullite and corundum. Their bulk density and thermal conductivity decrease in the order of using kaolin, andalusite, kyanite and sillimanite as the Al₂O₃-SiO₂ raw material, but their apparent porosity increases. Moreover, in the sample with kaolin, the bonding between anorthite crystals on the pore walls is closer than that of the other samples, which is conducive to increasing the cold crushing strength. The bonding between anorthite crystals on pore walls gradually decreases in the order of using kyanite, andalusite and sillimanite as the Al₂O₃-SiO₂ raw material, thus their cold crushing strength decreases accordingly. In comprehensive consideration, the properties of the sample from kyanite are the optimal. Its apparent porosity, thermal conductivity and cold crushing strength are 84.6%, 0.141 W·m^-1·K^-1 and 1.89 MPa, respectively.

Magnesia-calcium materials have stable hot performance, good resistance to the erosion and corrosion of liquid steel and steel slag, and a special role in purifying liquid steel, so they are widely used in iron and steel industry. However, hydration of magnesia-calcium materials seriously restricts their use, so researches have been done to improve their hydration resistance, obtaining a series of achievements. In this paper, the improvements on the hydration resistance of magnesia-calcium materials by additives in recent 20 years were presented, and their mechanisms were summarized.

To broaden the application of SiO₂ sol-bonded castables, using micro- or nano-Al₂O₃ powder and SiO₂ gel powder as the main raw materials, the effects of CaO impurity on the formation of mullite by the reaction of Al₂O₃ and SiO₂ at different temperatures (1 350, 1 400, 1 500, and 1 600 ℃) in different atmospheres (oxidation atmosphere and reduction atmosphere) were studied. The results show that in the oxidizing atmosphere, the introduction of CaO can promote the formation of mullite. When the temperature increases from 1 350 ℃ to 1 600 ℃, the amount of mullite formed gradually increases. In the reducing atmosphere, the introduction of CaO is not conducive to the formation of mullite, and the amount of mullite decreases with the increasing temperature. The smaller the particle size of Al₂O₃, the more easily it reacts with SiO₂ gel powder to form mullite.

Fiber products for microwave kilns were prepared using alumina fibers with alumina contents of 72 mass% and 80 mass%, and calcined alumina powder (4-6 μm) as the main raw materials, silica sol as the binder, and cationic starch as the flocculant. Effects of different raw materials and their additions on the wave transparency of fiber products were researched. The results show that as the alumina fiber (72%) addition increases, the heating rate of the samples first decreases and then increases, and the corresponding wave transparency of the sample first increases and then decreases. When the alumina fibers addition is 40 mass% and the alumina powder addition is 30 mass%, the prepared microwave kiln lining material has a higher mullite content, which improves the wave transparency of the sample. The sample prepared from alumina fibers with an alumina content of 80% has a suitable glass-mullite phase ratio, performs lower overall dielectric constant and good wave transparency, and is a suitable lining material for microwave kilns.

Aiming at improving the properties of magnesia carbon materials, silicon aluminum carbide (Al₄SiC₄) containing materials were prepared using industrial aluminum powder, silicon carbide powder, and graphite as raw materials, and activated alumina powder as an additive, mixing thoroughly, pressing into cylinders and then firing at 1 200 ℃ for 30 min in a carbon embedded atmosphere by the microwave method. The effects of the aluminum powder addition (20% and 24%, by mass) and activated alumina powder addition (0, 3%, 5% and 7%, by mass) on the microwave synthesis of Al₄SiC₄ as well as the effect of the obtained Al₄SiC₄ containing material on the properties of magnesia carbon bricks were studied. The results show that: compared with the samples with 20% aluminum powder, those with 24% aluminum powder generate more Al₄SiC₄. With the activated alumina powder addition increasing from 0 to 7%, the amount of Al₄SiC₄ generated increases first and then decreases. Compared with the sample without activated alumina powder, the samples with activated alumina powder show lower bulk density and higher apparent porosity. With the activated alumina powder addition increasing from 3% to 7%, the bulk density of the samples increases first and then decreases, while the apparent porosity of the samples shows an opposite trend. The optimal additions are 24% aluminum powder and 5% activated alumina powder, and Al₄SiC₄ synthesized in this sample has a hexagonal plate structure. With the synthesized Al₄SiC₄ containing material added, the magnesia carbon brick has slightly increased cold modulus of rupture, basically the same modulus of elasticity and improved oxidation resistance.