CaO pellets with different porosity were carbonated at 700℃ in CO2 atmosphere. The carbonation rate was controlled by the diffusion of CO2, regardless of the difference in porosities. For the low-porosity pellet, carbonation reaction only occurred on the surface, with a denseCaCO3 film thus formed, which combined well with the substrate material; while for the pellet of high-porosity, the carbonation reaction occurred simultaneously both on surface and inside pores, and each CaO grain was surrounded by CaCO3 film that contained microfissures. Hydration test results showed that carbonation treatment could effectively improve the hydration resistance of CaO materials regardless of porosity, but the carbonated high-porosity pellet was prone to breakage due to poor combination between the carbonated CaO grains. Therefore, for the purpose to improve the hydration resistance by carbonation treatment, it is recommended that the CaO materials should be either with less appreciable apparent porosity or with a limited carbonation ratio for the high-porosity CaO material.

MgO–CaO refractories added with different sized ZrO2 powders were sintered at 1600℃, the effect of the ZrO2 powders on performance of MgO–CaO refractories was investigated. The results showed that the densification of the MgO–CaO refractories was appreciably promoted when a small amount of ZrO2 was added owing to the formation of small size CaZrO3 facilitated to sintering, and the densification was promoted further with increasing the amount of ZrO2 due to the volume expansion caused by the reaction of the added ZrO2 and CaO to form CaZrO3 in the refractories, and the addition of nano-sized ZrO2 was more effective. The thermal shock resistance of the MgO–CaO refractories was improved by modification of the microstructure due to the formed CaZrO3 particles that predominately located on the grain boundaries and triple points in the whole microstructure, and the addition of nano-sized ZrO2 was more effective attributed to its well dispersion and the critical addition amount was effectively decreased to 6%. The slaking resistance of the MgO–CaO refractories was appreciably improved by addition of ZrO2 due to its effect on decreasing the amount of free CaO in the refractories, promotion of densification as well as modification of microstructure, the nano-sized ZrO2 addition was more effective due to its higher activity. The slag corrosion resistance of the MgO–CaO refractories was enhanced by addition of ZrO2 due to the increase of the viscosity of the liquid phase and thus inhibited further penetration of slag at elevated temperatures.

The mixing behaviour in a 150t ladle furnace induced by two-nozzle jetting was investigated on the basis of a water model simulation of 1: 4. The effects of nozzle arrangements, including separation angle, radial position and asymmetry as well as tracer adding position, on the mixing time were studied. The most favourable mixing was achieved when the two nozzles were symmetrically arranged at half radii in the ladle, with 45

The effect of SiC used as antioxidant in carbon-containing CaO–ZrO2 refractories and the behaviour of SiC in CO gas were studied. SiC was found to react initially with CO to form SiO2(s) and C(s) at 1200℃, and then the formed SiO2 reacted with CaO in the refractories to form belite (2CaO·SiO2). The refractory microstructure was modified by addition of SiC. Due to the deposition of SiO2 in the large (2–10 μm) pores of the refractory through the reaction of SiO(g) with CO, the percentage of large pores decreased and a dense layer, mainly consisting of belite, was formed near the surface of the refractory after it was heated at high temperature (1500℃). The oxidation resistance of CaO–ZrO2–C refractories was improved by reaction of SiC with CO to deposit C(s) and decrease the size of the large pores. The oxidation resistance of such refractories can be improved significantly when such a dense layer is formed near their surfaces.

An alumina–magnesia precast block was prepared by using high-alumina fused corundum as aggregate, and fused magnesia, ultra-fine Al2O3 and SiO2 powders as matrix materials. A small linear expansion for the precast block was achieved through spinel formation from the reaction of MgO with Al2O3 in the matrix. The precast block showed a lower apparent porosity, higher modulus of rupture and better slag corrosion resistance compared to the traditional Al2O3–MgO–C brick. In addition, the practical application of the precast block to the ladle lining proved it to possess a better thermal insulation which could effectively prevent the temperature drop of molten steel during the refining process. It can be considered that the alumina–magnesia precast block could possibly be applied as a new type of ladle lining material for the production of low-carbon and ultra-low-carbon steel.