China's Refractories

Traditional magnesia-based refractories face challenges such as high thermal conductivity and poor slag penetration resistance, which contradict the energy efficiency requirements of modern metallurgy. In this study, microporous magnesia was prepared using low-grade magnesite via the one-step sintering method. The microstructure and properties of microporous magnesia prepared by high-silicon and high-calcium magnesites calcined at various temperatures were compared. The pore structure and phase evolution were analyzed, the effect of which on the properties of lightweight magnesia-based dry vibration mix was discussed. The results indicated that within high-silicon magnesite, SiO₂ initially reacted with MgO to form Mg₂SiO₄, which gradually reacted with CaO impurities as the temperature increased transforming into a MgO-CaO-SiO₂ ternary liquid phase and uniformly permeated along the grain boundaries. Due to the bridging effect of strip-like CaO in high-calcium magnesite, the reorganization and sintering of MgO grains at high temperatures were inhibited, resulting in the presence of a significant number of elongated pores within the magnesia after calcination at various temperatures, which was detrimental to the mechanical properties and slag resistance. The microporous MgO prepared by high-silicon magnesite at 1 700 °C exhibited the superior physical properties. The microporous MgO aggregates had a stronger interlocking force with the matrix, resulting in a greater bonding strength. Moreover, the micropores not only effectively reduced the thermal conductivity but also facilitated the supersaturated precipitation of molten slag, hindering further penetration. Compared to the dry vibration mix prepared by fused MgO, the lightweight magnesia-based dry vibration mix prepared with the high-silicon magnesite exhibited higher mechanical strength (~40% increase) and thermal insulation performance (0.870 W · (m · K)^-1 at 1 000 °C), and improved slag resistance.

MgO-CaO refractories are widely used in the iron and steel metallurgy industry due to their advantages of purifying molten steel, high refractoriness, good thermal shock resistance, and excellent corrosion resistance to basic slags. However, hydration occurs during the manufacturing, storage, and transportation of refractories, which severely limits their application. MgO-CaO clinker is the main raw material for MgO-CaO refractories, and its hydration resistance determines the development of the latter case. Herein, the MgO-CaO clinker was modified using myristic acid as the modifying agent by the liquid-phase deposition method. The effects of the particle size of the raw materials, concentration of myristic acid, treatment temperature and time on the phase composition and hydration resistance of the modified MgO-CaO clinkers were investigated in detail. The results show that the samples with an agent concentration of 0.25 mol·L^-1 and treated at 25 °C for 1 h exhibit the optimal hydration resistance properties, namely a low hydration mass gain rate (0.23%) and a large water contact angle (152.9°).

Mullite-silica rich glass (MSRG) composites are a more efficient material than chamotte for industrial utilization of clay in refractory applications. The properties of the MSRG composites depend on the amount and composition of the mullite and glass phases, which are related to the chemical composition of the MSRG composites based on clay. In the present work, the relationship between the phase and the chemical composition of the MSRG composites, and the effects of the chemical composition of the glass phase on the viscosity and coefficient of thermal expansion (CTE) of the glass phase were discussed on the basis of the measurements on 17 MSRG composite samples produced from clay. It is found that the Al₂O₃/SiO₂ ratio (A/S ratio) in clay strongly affects the amount of the mullite and glass phases in the MSRG composites, and the distributions of SiO₂, TiO₂ and Fe₂O₃ contents in the mullite and glass phases. With the increase of the A/S ratio of clay, the mullite content increases but the the glass phase content decreases in the MSRG composites. The viscosity and CTE of the glass phase depend on its A/S ratio and the amount of impurity oxides. When the A/S ratio in the glass phase is less than 0.15, the viscosity of the liquid formed by the melting of the glass phase at elevated temperatures rapidly increases with the decrease in the A/S ratio. The CTE of the glass phase depends on the contents of SiO₂ and (K₂O+Na₂O).

High-performance alumina-magnesia castables were developed with the addition of nano-CaCO₃ and nano-hydromagnesite. To further understand their dynamic failure mechanism, the quantitative investigation via the employment of the Split-Hopkinson pressure bar (SHPB) method was adopted to test the dynamic failure behavior of alumina-magnesia castables under various impact velocities. The results demonstrate that the greater the impact velocity, the more intense the sample damage. The dynamic compressive stress, the ultimate strain, and the strain energy of all samples display a strain rate hardening effect, and this phenomenon is more conspicuous in the samples incorporating nano-additives. The nano-additives show a positive influence on the dynamic mechanical properties of the castables.

The penetration of ladle slag into refractory linings is an essential process in service, and the mechanical properties of the refractory castables are affected by the location and content of slag in the refractory castables. In this work, ladle slag was added into Al₂O₃-MgO refractory castables and its influence on the microstructure evolution, mechanical properties and thermal shock resistance of the castables was investigated. The phase composition and contents of the castables during the corrosion process were calculated by FactSage TM (6.2) and studied. The results indicate that the residual strength decreases as the ladle slag addition increases from 0 to 6 mass%. While the hot modulus of rupture of the castable with 6% ladle slag significantly decreases by approximately 80% compared with the one without ladle slag. The elastic modulus and CMOR of the castables decrease with slag-adding, which leads to the increase of liquid phase contents inside the samples.

Utilizing phosphorus tailings as the raw material for foam concrete is a key approach to achieving sustainable and efficient resource utilization. During the preparation of phosphorus tailings-based foam concrete, slurry performance is critical to the successful production. Phosphorus tailings, cement and microsilica were used to prepare foam concrete slurry in this study. A rheometer was employed as a test tool to measure the variation of linear viscoelastic zone (LVR), viscosity, and yield stress of the slurries with different cement contents. The results indicate that the phosphorus tailings-cement-microsilica slurry exhibits shear-thinning properties, which aligns well with the Herschel-Bulkley model, showing a high degree of correlation. As the cement content increases, the energy storage modulus of the slurry rises, and the LVR length shows a nonlinear trend. The LVR reaches its maximum length of 0.04% when the cement content is 6 mass% or 8 mass%. The increment of the cement content leads to a more intricate internal network structure, which hinders the reconstruction rate of the flocculated structure after high-shear deformation.