Qifeng Shu

New method for viscosity estimation of slags in the CaO–FeO–MgO–MnO–SiO2 system using optical basicity

Abstract Several models have been proposed to estimate the viscosity of molten slag using optical basicity. In this work, a new method for viscosity estimation of silicate slag using optical basicity has been proposed. The temperature dependence of viscosity was described by the general Arrhenius equation, and the contributions of bridging oxygen (O0), non-bridging oxygen (O–) and free oxygen (O2–) to viscous activation energy in this equation were taken into account. Compositions of three types of oxygen were calculated from optical basicity using the Toop–Samis model combined with the method proposed by Ottonello and Moretti. The present method has been applied to estimate the viscosity of silicate slag in CaO–FeO–MgO–MnO–SiO2 system. The comparison between estimated and experimental values shows good agreements, with a mean deviation of ∼20%.

Structure and Crystallization Kinetics of Glassy CaO-Al2O3-SiO2-CaF2-Na2O Mold Fluxes with Varying Basicity

The structure and the crystallization kinetics of CaO-Al2O3-SiO2-CaF2-Na2O mold fluxes with varying basicities were investigated by solid-state 29Si nuclear magnetic resonance with magic angular spinning (MAS-NMR) and differential thermal analysis (DTA) technique, respectively. 29Si MAS-NMR study indicated that the increase of basicity decreased the degree of polymerization of mold fluxes. With the increasing basicity, Q0, Q2, and Q3 gradually decreased, while Q1 gradually increased, and the overall degree of polymerization was reduced. Crystallization analysis showed the cuspidine first crystallized from glass, and wollastonite crystal crystallized at elevated temperature for the samples with basicity (defined as CaO/SiO2 mass ratio) values of 0.9 and 1.0, respectively. Only cuspidine was found to crystallize from glass for the samples with basicity values of 1.1 and 1.2, indicating that the crystallization of wollastonite was suppressed with the increase of basicity. Crystallization kinetics analysis by DTA and field emission scanning electron microscopy equipped with energy dispersive spectroscopy investigation showed that growth mechanism of cuspidine is mainly of the diffusion-controlled three-dimensional growth with the increasing number of nuclei during heating. Activation energies for growth of cuspidine decreased with the increasing basicity of mold flux, which indicated that the crystallization ability was enhanced with the increase of basicity. The relationship between structure and crystallization of mold fluxes was established.

Effect of Agitation on Crystallization Behavior of CaO-Al2O3-SiO2-Na2O-CaF2 Mold Fluxes with Varying Basicity

The effect of agitation on crystallization behaviors of CaO-Al2O3-SiO2-Na2O-CaF2 mold fluxes with basicity of 1.1 and 1.2 was investigated. It was found that crystallization temperatures of agitated samples were higher than those of static samples. The morphology of cuspidine shifted from dendrites to facet crystals with the decrease of temperature. The agitation was conducive to the formation of small dendritic cuspidine and could lead to crystals with smaller size. Crystalline fraction could be significantly enhanced by agitation at the initial stage of crystallization.

Effect of B2O3 on Slag-Metal Reaction between CaO-Al2O3-Based Mold Flux and High Aluminum Steel

Abstract The effect of B2O3 on slag-metal reaction between CaO-Al2O3-based mold flux and high aluminum steel was investigated. The results showed that the addition of 5 % B2O3, the slag-metal reaction hardly occurred. When the content of B2O3 was increased, the reaction rate increased rapidly. This indicated if only considering the slag-metal reaction, it’s better for high aluminum steel casting if the addition content of B2O3 is less than 5%. The chemical reaction was greatly influenced by the reaction time. With higher content of aluminum ([Al]=0.1 %), the early stage of reaction was greatly affected by the reaction time, and furtherly, the influence was decreased. When the aluminum content was increased, the effect of [Al] on the slag-metal reaction was comparatively small in the initial 10 min, and the content of [B] was increased slightly. But when the reaction time increased to 1 hour, the slag-metal reaction acutely occurred, and the content of [B] increased rapidly.

Effects of oxygen atmosphere, FeOx and basicity on mineralogical phases of CaO–SiO2–MgO–Al2O3–FetO–P2O5 steelmaking slag

ABSTRACT The mineralogical phase of slag after crystallisation is essential to utilisation of steelmaking slag. The mineralogical phases of cooled multicomponent CaO–SiO2–MgO–Al2O3–FetO–P2O5 slag with different iron oxide contents and basicities (defined as the ratio of mass percentage of CaO to mass percentage of SiO2 (w(CaO)/w(SiO2))) in different atmospheres were investigated in the present work by scanning electronic microscopy and energy dispersed spectroscopy analysis and X-ray diffraction. The mineralogical phases in steelmaking slag cooled in argon are mainly nCa2SiO4-Ca3(PO4)2 (thereafter nC2S-C3P) solid solution, (Fe, Mn, Mg)O (RO) phase. Some CaMgSiO4 phases could be found in slag with lower basicity. The mineralogical phases in steelmaking slag cooled in air are mainly nC2S-C3P solid solution, spinel phase. The overall crystallisation of slag cooled in both argon and air was enhanced with increasing basicity. However, the crystal sizes become smaller in sample with high basicity. The Fe-enriched phases were transformed from non-faceted RO phase in sample cooled in argon to faceted spinel phases in sample cooled in air. The crystallisation of slag cooled in both argon and air was promoted with increasing FeOx content. The phosphorus content in solid solution was elevated with decreasing basicity and increasing FeOx content. It was implied by the present work that appropriate basicity and air oxidation would be beneficial to magnetic separation and phosphorus utilisation.

Reduction of synthetic stainless steel slags by aluminium

ABSTRACT One of the most efficient ways to eliminate the harm of chromium oxide in stainless steel slag is to reduce chromium oxide in stainless steel slag using aluminium. In the present work, the Al reduction of synthetic CaO–SiO2–Al2O3–MgO–Fe2O3–Cr2O3 stainless steelmaking slags at different conditions, including temperature, slag basicity and Al amount was investigated to get optimal conditions for the reduction and the metal–slag separation. It was found that the agglomeration of metal droplets and metal–slag separations were improved by increasing temperature. The reduction degrees of SiO2, Fe2O3 and Cr2O3 were enhanced with increasing basicity of slag. The addition of CaF2 in slag leads to better agglomerations of metal droplets and metal–slag separations. The highest reduction degree of chromium could reach 99% in slag with basicity of 2 at 1873 K.