China's Refractories

Porous mullite-bonded SiC membrane supports for hot-gas cleaning were prepared by an in situ reaction bonding process. Their thermal shock resistance was evaluated as a function of the thermal shock temperature and thermal shock cycles by an instantaneous heating-air cooling technique, comparing with that of the commercial clay-bonded SiC support with similar SiC grain size, pore size and open porosity. It was found that the quenched specimens bonded by mullite exhibited a continuous increase in the cold modulus of rupture with the thermal shock temperature increasing from 400 °C to 1 200 °C, and the strength reached 24.7 MPa with an increase rate of 30% after thermal shock at 1 200 °C. This surprising behavior was quite different from that of the clay-bonded specimens which exhibited a gradual strength decrease when the thermal shock temperature exceeds 800 °C. With the increase of the thermal shock cycles at the quenching temperature of 1 200 °C, the cold modulus of rupture of the mullite-bonded quenched specimens initially increased, and then remained unchanged. The thermal shock damage of the mullite-bonded SiC supports was avoided under the thermal shock test conditions. It can be attributed to the similar thermophysical properties and good chemical compatibility between mullite and SiC. The supports after high temperature thermal shock were obviously enhanced by the self-crack-healing ability of mullite-based binder and residual stress. Therefore, the porous SiC ceramics bonded by mullite exhibit excellent thermal shock resistance, and have greater potential than those bonded by clay for high temperature gas filtration and other applications, where cyclic thermal shock is desired for continuous operations.

ISO 16206: 2025 Phase quantitative analysis of residual quartz in silica bricks—X-ray diffraction method, as an important international standard in the field of refractories, was jointly led and developed by Sinosteel Luoyang Institute of Refractories Research Co., Ltd. (short for Sinosteel LIRR) and Sinosteel Luonai Technology Co., Ltd., and was officially issued and implemented in July 2025. This paper elaborates on the development background, project approval process and core technical content of the standard, analyzes the key technical difficulties and solutions during the standard development, and discusses the far-reaching impacts of the standard’s implementation on global silica brick production, testing and international trade.

To broaden the design and development of high-performance porous ceramics, mullite porous ceramics were prepared by the direct foaming method, using industrial alumina and Guangxi white clay as raw materials, α-sodium olefin sulfonate as the foaming agent, modified polyethoxylated silicone (MPS) microemulsion as the foam stabiliser, and ammonium citrate as the dispersant. The effects of the MPS addition (0.2%, 0.3% and 0.4%, by mass) and the stirring time (5, 10 and 15 min) on the microstructure and properties of the ceramics were investigated. The results demonstrate that the main crystalline phase of the ceramics is mullite, with corundum as the secondary phase. With the increase in the MPS addition, the pore size distribution of the ceramics becomes more uniform while the median pore diameter decreases, and the cold compressive strength and bulk density increase. With the prolongation of the stirring time, the porosity and median pore diameter of the ceramics decrease first and then increase, while the cold compressive strength and bulk density show an opposite trend. With 0.3% MPS and a stirring time of 10 min, the mullite-based porous ceramics have the optimal performance.

Al₂O₃-SiC-C materials were prepared using recycled corundum (1-3 and 3-5 mm), white fused corundum (≤1 mm), α-Al₂O₃ micropowder (≤10 μm), flake graphite (≤50 μm) and silicon carbide (≤1 mm) as main starting materials, silicon powder (≤74 μm) as the antioxidant, and thermosetting phenolic resin with a carbon residue of about 45% as the binder. The effects of the zirconia corundum (AZ40, ≤74 μm) addition (0, 3%, 6%, 9%, and 12%, by mass) on the structure and properties of the Al₂O₃-SiC-C materials were investigated. The fracture morphology of the samples after heat treatment was observed using a field emission scanning electron microscope, and the structure was analyzed. The results show that: (1) with the increase of the AZ40 addition, the bulk density, cold modulus of rupture, cold compressive strength, hot modulus of rupture, and the retention ratio of the cold modulus of rupture of the samples all increase first and then decrease, while the apparent porosity and oxidation index change in reverse; (2) with the AZ40 addition increasing to 12%, the sample performs poorer mechanical and antioxidant properties than the one without AZ40, indicating that an appropriate AZ40 addition is beneficial to improving the mechanical properties, thermal shock resistance and oxidation resistance of the Al₂O₃-SiC-C materials; (3) the sample with 3% AZ40 exhibits the best comprehensive performance.

To address the harsh service conditions in rotary hearth furnaces for solid waste treatment, such as high temperatures, strong corrosion, and rapid thermal cycling, as well as the issue that traditional cement-bonded refractories introduce CaO and form low-melting-point phases thus leading to spalling and failure, an Al₂O₃-SiC refractory material was prepared using high-alumina aggregates, corundum fine powder, silica fume, alumina micropowder, and silicon carbide as main raw materials, with a novel nano-composite sol as the binder. The mechanical properties, slag corrosion resistance, thermal shock resistance, and wear resistance of the material were investigated and compared with those of conventional cement-bonded materials. The results show that the nano-composite sol-bonded material completely avoids the introduction of CaO. A three-dimensional siloxane network formed through dehydration reactions significantly enhances the overall performance of the material. It achieves 302 thermal shock cycles and an abrasion loss of only 4.12 cm³. The cold modulus of rupture and cold compressive strength of the heat treated specimens are superior to those of cement-bonded materials, and their slag corrosion resistance is markedly improved. At high temperatures, phases such as Al-Fe composite spinel and leucite are generated in the material, forming a protective slag layer, which effectively blocks further molten slag corrosion, thereby extending the service life of the material.

Affected by increasingly stringent environmental protection policies, the quality fluctuation of industrial lime milk has become a common bottleneck restricting the stable production of silica bricks, leading to inhomogeneous crystalline phases and unstable performance. In this study, silica bricks were prepared using high-purity silica as the main raw material, and CaO-based mineralizers were introduced through three methods: conventional industrial lime milk, direct mixing of Ca(OH)₂ powder with water, and pre-dispersed Ca(OH)₂ emulsion. The effects of different Ca(OH)₂ introduction methods on the phase transformation, microstructure and properties of the silica bricks were investigated. The results show that the silica bricks fabricated with pre-dispersed Ca(OH)₂ emulsion present equivalent comprehensive properties to those of the traditional lime milk process. Compared with the traditional specimen, the relative β-tridymite content increases by 12.0% and the residual quartz content decreases to 2.0%. The pre-dispersed emulsion promotes sufficient phase transformation from quartz to β-tridymite and optimizes the microstructure via four core mechanisms, including thermal decomposition matching, nano-activation effect, liquid phase regulation and lattice defect strengthening. It can completely replace traditional industrial lime milk as a mineralizer, fundamentally solving the production stability problem caused by unstable mineralizer activity and showing outstanding industrial application potential.

To enhance the mechanical properties of lightweight insulating materials, this work adopted expanded vermiculite as the aggregates and systematically investigated the effects of the expanded vermiculite addition, ratio of silica fume to fumed silica, and fiber dosage on the cold compressive strength and thermal conductivity of the composites. The bulk density and cold compressive strength of the samples were tested, and their microstructure was observed. The results show that: (1) as the expanded vermiculite addition increases, the required molding pressure increases and the bulk density of the samples increases; (2) when the ratio of silica fume to fumed silica is 1:2, the cold compressive strength of the composites is the highest; (3) an increase in the fiber dosage intensifies the tendency of fiber agglomeration, which is not conducive to the uniform dispersion of fibers; (4) when the expanded vermiculite addition is 40%, the ratio of silica fume to fumed silica is 1:2, and the fiber dosage is 2%, the comprehensive performance of the composite is relatively good, with bulk density of 0.51 g·cm^-3, cold compressive strength of 0.618 MPa, and thermal conductivity of 0.057 W·m^-1·K^-1 at 200 °C.