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A deep understanding of the behavior of nonmetallic inclusions is essential for steel cleanliness control. The behavior of alumina inclusions at the liquid iron/argon gas interface is investigated using a high‐temperature confocal scanning laser microscope. The obtained images are used to determine the moving velocity of the inclusions on the interface. The obtained experimental data are quantitatively evaluated using the lateral capillary interaction model for multipole orders established by Danov–Kralchevsky while taking into account the resistive drag force. The attraction forces calculated from these data are in the range between ≈10−13 and ≈10−11 N. The best‐fitting model is assigned for each case. The multipole models almost counterbalance the drag force, indicating a good interpretation of the interaction between the inclusions. Moreover, the acting length of this interaction is examined and compared to the previous work on Ce2O3 inclusions. It is found that alumina inclusions generally exhibit a larger acting length at a large critical radius and a smaller acting length at a small critical radius when comparing them to their counterpart cerium oxide inclusions. Considering the particle shapes, high shape irregularity is better interpreted by higher orders of the multipoles. [ABSTRACT FROM AUTHOR]

Basic oxygen furnace (BOF) slag is a byproduct in the steel making process and is produced in considerable amounts. Thus, its valorization is important. Additives such as Al2O3 can be utilized to modify the composition and mineralogy of the slag provided that a fast and effective dissolution of these additives in molten slags can be ensured. With this in mind, the dissolution of Al2O3 particles in molten BOF slag has been investigated between 1500 and 1600 °C. In all cases, a dissolution zone forms around the dissolving particle which limits the dissolution rate in the melt under natural convection conditions. The dissolution in the current system is found to be an indirect process, wherein crystalline reaction products like CaAl4O7 (CA2) and CaAl2O4 (CA) form on the surface of the particles. CA forms at 1500 °C and CA2 at 1600 °C. These reaction products form a continuous layer on the surface of the dissolving particles but the thickness of this reaction layer remains limited. The experimental data have been utilized to evaluate the dissolution paths. Near the Al2O3/slag interface, the inter-diffusion of Al2O3 and CaO occurs due to which the dissolution path shifts towards the Al2O3-CaO binary system. A phenomenological model is presented to explain the evolution of the dissolution process in the current system, wherein the kinetics of the process is used to explain the reaction products formed at 1500 °C and 1600 °C. [ABSTRACT FROM AUTHOR]

Steel reoxidation in the tundish has a significant influence on the steel cleanliness and therefore on the mechanical properties of the final product. In the present work, the steel reoxidation by two types of gunning mass (GM), viz. magnesia- and alumina-based GM, and two types of tundish slag, viz. lime-alumina-silica and lime-alumina slags, has been investigated. The evolution of the steel composition during the test was analyzed and predicted based on thermodynamic and kinetic considerations. The calculated steel composition agrees well with measured values, when assuming the mass transfer in slag phase limits the reoxidation reactions. The oxidation capacity of the gunning mass and tundish slag is quantified by calculating the oxygen amount supplied from the GM and the slag to the steel phase. It was found that compared to alumina GM, magnesia GM exhibits a stronger oxidation capacity due to its higher content of reducible oxides (10 wt pct SiO + 6 wt pct FeO). Compared to lime-alumina-silica tundish slag, lime-alumina slag (with more FeO + MnO contents) provides more oxygen to the molten steel in the present experimental conditions and consequently shows a stronger oxidation capacity. [ABSTRACT FROM AUTHOR]

The slag valorisation is of significant importance in alleviating the problems of environmental impact and resource shortage. Since the slag's electrical conductivity is sensitive to a minor change in its microstructure, conductivity measurements provide a promising method to monitor online slag solidification during hot stage processing. In this work, solidification of a synthetic 34 wt% CaO–19 wt% Al 2 O 3 –39 wt% SiO 2 –8 wt% MgO (CASM) slag was studied in situ using confocal scanning laser microscopy (CSLM), while simultaneously measuring the slag's electrical conductivity with impedance spectroscopy. After the measurement, the microstructure of the quenched slag samples was analysed using scanning electron microscopy (SEM). A quantitative relationship was established between the slag's electrical conductivity and its liquid fraction under isothermal conditions. This relationship can be used for the development of online monitoring systems for the precise control of slag crystallization, to obtain suitable mineralogy for high added value applications. [Display omitted] [ABSTRACT FROM AUTHOR]

The ladle treatment of a 18 pct Cr-9 pct Ni stainless steel, with desulfurization as its main purpose, was simulated on a laboratory scale. The influence of the top slag chemistry on the steel cleanliness was evaluated. A higher steel cleanliness was obtained with an optimized lime-alumina-based slag than with a lime-fluorspar-based slag. The inclusions were found to be mainly in the form of oxysulfide; the alumina content in the inclusions first increased and subsequently showed a slow drop, while the sulfide content decreased during the treatment. The equilibrium between steel and inclusions was found to be more easily reached than that between slag and steel. A slag-steel kinetic model was used to predict the steel chemistry evolution during the treatment. Furthermore, a slag-steel-inclusions interaction kinetic model was developed to calculate the change of alumina content in the inclusions during the ladle treatment. The sulfide content of inclusions was also calculated and compared with the measured values. [ABSTRACT FROM AUTHOR]

A strong magnetic field, e.g., >10 T, is considered an important tool in the process of small nonmetallic inclusions removal and related anisotropic materials preparation. In the present paper, a model system of aluminum containing alumina particles is used to investigate the strong magnetic field effects. Considerable segregation is induced by the applied gradient magnetic field, whereas no segregation is observed in a gravity field because of the convection. A high gradient magnetic field, together with the particle size and treatment time, is an important factor in generating the segregation. At the same time, magnetic alignment is detected after the strong magnetic field treatment. The (00l) crystal planes of alumina are found to be aligned to the strong magnetic field direction. Experimental results agree with the theoretical calculations based on the theory of magnetic energy. Additionally, the rotation time for the alignment is estimated and the time for alumina particles of 15 μm is found to be <1 s. However, the alignment is easily disturbed by the convection during the quenching outside of the strong magnet, especially for small particles where the rotation time is much shorter. The present results offer a better understanding of the strong magnetic field effects on the behavior of nonmagnetic particles in a conductive fluid. [ABSTRACT FROM AUTHOR]

Slag solidification behavior significantly influences the tapping of the Zn fuming process and slag valorization. In this work, the effect of ZnO and CaO concentration on slag solidification was investigated under a pO 2 of approximately 10−10 atm using confocal laser scanning microscopy (CLSM) at various cooling rates. It was concluded that in the low CaO slag, the ZnO increased the onset formation temperature of the fayalite phase. An increase in CaO concentration facilitated wustite precipitation and prevented spinel formation in the slag at cooling rates exceeding 1 °C/s, while it enhanced melilite generation and inhibited fayalite precipitation in the slag at cooling rates below 1 °C/s. Furthermore, the slag mineralogy was studied as a function of equilibration temperature and CaO concentration of the slag through water quenching experiments under the Ar atmosphere. When slags with a CaO concentration of 3–20 wt% were quenched from 1050 to 1200 °C, the amorphous and spinel phases were observed in all quenched slags, whereas the wustite phase was only identified in slags with a CaO concentration above 10 wt%. Additionally, the fayalite phase was detected in slags containing 3–5 wt% CaO, quenched at temperatures of 1150–1050 °C. Notably, as the quenching temperature decreases and the CaO concentration increases, the observed phases in the quenched slag become more complex, and the solid particles grow coarser. The FeO t -SiO 2 -(4.7–5.7 wt%)ZnO-(8.3–10.1 wt%)Al 2 O 3 –CaO-1.3 wt%MgO-1.1 wt%Cr 2 O 3 (FeO/SiO 2 = 1.44) slags with a CaO concentration of below 20 wt% is suggested to be quenched from 1150 °C or 1200 °C to prevent the precipitation of a SiO 2 -containing phase and coarse wustite. [ABSTRACT FROM AUTHOR]

CaO solubility in the FeO t -SiO 2 -CaO-Al 2 O 3 -(ZnO, Cr 2 O 3) system has been experimentally investigated at 1200 and 1250 °C under pO 2 of 10−10 atm. Synthetic slags rich in CaO were equilibrated at desired temperatures, followed by water quenching, and analyzed using electron probe X-ray microanalysis (EPMA). In the quaternary FeO t -SiO 2 -CaO-(6 to 10 wt%) Al 2 O 3 system, CaO solubility exhibits a linear increase from 27.5 to 36.9 wt% with decreasing the FeO/SiO 2 (F/S) ratio from 1.66 to 0.62 at 1250 °C. Similarly, at 1200 °C, the CaO solubility increases from 24.9 to 30.8 wt% as the F/S ratio drops from 1.25 to 0.56. Excessive CaO addition to the slags results in the precipitation of melilite phase. Wustite is observed in the F/S ratio range of 1.66 to 1.0, and the size of wustite particles decreases as the F/S ratio decreases. At both 1200 and 1250 °C, the liquid phase with an F/S ratio below 0.42 is in equilibrium with wollastonite (CaSiO 3) in the FeO t -SiO 2 -CaO-Al 2 O 3 system. The addition of a small amount of ZnO (0.4–1.1 wt%) in the slags leads to a slight decrease in CaO solubility by 1–3 wt%, while the presence of 3.3–8.1 wt% of ZnO in the slags results in a decrease of 5–11 wt% in CaO solubility. Similar to the FeO t -SiO 2 -CaO-Al 2 O 3 system, the equilibrated CaO-containing solid phase is also melilite in the FeO t -SiO 2 -CaO-Al 2 O 3 -ZnO system. With the addition of a small amount of Cr 2 O 3 (1.0 wt%) to the FeO t -SiO 2 -CaO-Al 2 O 3 -ZnO system, spinel and dicalcium silicate (Ca 2 SiO 4) precipitate from the liquid slag, and the dissolved CaO concentration in liquid slag increases by 1–3.6 wt% in the F/S ratio range of 1.58 to 0.84, compared to the Cr 2 O 3 -free system. [ABSTRACT FROM AUTHOR]

Isothermal crystallization of a hexagonal crystal (Wollastonite) in ternary melts (CaO-Al 2 O 3 -SiO 2 ) was simulated by quantitative phase-field simulation and analytical modelling. The dependence of initial composition, undercooling, interfacial energy and anisotropy strength on the growth behavior of Wollastonite was comprehensively investigated. According to simulation results, a transition from flat to dendritic growth of CaSiO 3 occurs; the formation of dendritic Wollastonite is favorable at a lower Al 2 O 3 content, a lower temperature and a higher anisotropy. When temperature increases, the transition prefers taking place at lower interface energy. Simulations also show that the tip velocity firstly increases until it reaches a maximum value and then decreases slowly with further decreasing the temperature, while the velocity only increases at a lower interfacial energy level. For anisotropy strength, its increase causes a higher tip velocity. Furthermore, validation of these parameter effects was performed by comparing the simulation results with an analytical model, showing quantitatively good agreement, when solute interaction was taken into account in the analytical model. [ABSTRACT FROM AUTHOR]

A quantitative phase-field model has been implemented to study the dissolution behavior of alumina (Al 2 O 3 ) into CaO–Al 2 O 3 –SiO 2 slags. The simulations allowed evaluating the influence of temperature and composition on the diffusion paths and dissolution rates of Al 2 O 3 into CaO–Al 2 O 3 –SiO 2 slags. The results obtained in the simulations are consistent with experimental observations and the predictions from an analytical dissolution model. The phase field simulations show that the dissolution rate of Al 2 O 3 increases with temperature. Increasing CaO at a fixed Al 2 O 3 content or decreasing Al 2 O 3 content at a fixed CaO/SiO 2 ratio also results in a higher dissolution rate of Al 2 O 3 . The results are further interpreted based on thermodynamic and kinetic considerations. [ABSTRACT FROM AUTHOR]

The precipitation of metallic Fe from the FeO t -SiO 2 -CaO-Al 2 O 3 –ZnO-(Cr 2 O 3) slag system can cause serious problems for the slag tapping and slag valorization. This study examines the impact of slag chemistry, oxygen partial pressure (pO 2), and temperature on Fe generation and ZnO reduction in the FeO t -SiO 2 -CaO-Al 2 O 3 –ZnO-(Cr 2 O 3) slag system and compares the results with those from FactSage calculation. Metallic Fe is observed in CaO-free slag with a FeO/(Al 2 O 3 +SiO 2) ratio above 1.22 under pO 2 of 1 × 10−12 atm at 1250 °C. As the CaO content increases to 29.7 wt%, the critical FeO/(Al 2 O 3 +SiO 2) ratio for Fe generation decreases to 0.53. The critical temperature for Fe precipitation under pO 2 of 1 × 10−12 atm is measured to be between 1200 and 1250 °C, while the critical pO 2 to prevent the metallic Fe formation was calculated to be in excess of 5 × 10−13 and 1 × 10−12 atm at 1200 and 1250 °C, respectively. ZnO can be reduced into metallic Zn at 1250 °C under pO 2 of 1 × 10−10 atm or below. The operational conditions for Zn fuming of the FeO t -SiO 2 -CaO-Al 2 O 3 –ZnO slags without Fe formation are recommended to be pO 2 of 1 × 10−12 atm at 1200 °C. [Display omitted] [ABSTRACT FROM AUTHOR]

The present study characterizes the evolution of oxides at the Al liquid/vapor interface by combining high-temperature wetting, droplet-pushing experiments, in-situ observation of oxide clusters, analysis of the quenched droplets and thermodynamic calculations. The droplet shape of liquid Al on alumina substrates is analyzed and the magnitude of its deviation from a spherical cap is considered as an indicator of the level of oxides present at the surface. Characterizing whether the sessile droplet recovers its spherical shape or not when pushing on its top part reveals that the oxides at the liquid/vapor interfaces become dense at low temperatures, but are almost completely removed above 1100 °C. In-situ observation of the oxides and the subsequent analysis of the quenched droplets confirm this evolution. Wetting experiments combined with 3D-rebuilted structures of quenched samples reveal that the presence of dense oxides prevents the spreading of liquid Al droplets. By thermodynamic calculations and measuring evaporation rates of droplets, it is confirmed that the Al 2 O gas produced by reaction between oxides and liquid Al contribute significantly to the oxides elimination at high temperatures. Our results are relevant for improving the control of the spreading of liquid metals among many high-temperature processes, including welding, coating and composites fabricating. [Display omitted] [ABSTRACT FROM AUTHOR]

To investigate the densification of porous alumina plugs, hydrogen measurements, using the Hydris probe system, were performed in molten steel with different oxygen levels at around 1600 °C. The oxygen contents in molten steel were controlled by Al and Fe-Si alloy additions to 664, 296, 92, 51 and 2.5 ppm, respectively. High oxygen levels (> = 92 ppm) in molten steel were found to favor the infiltration of steel into porous alumina plug. The infiltrating steel interacts with SiO 2 -containing phases and Al 2 O 3 inside the plug, forming liquid FeO n -Al 2 O 3 -SiO 2 slag and FeAl 2 O 4 (hercynite). These newly formed phases, along with the infiltrating steel fill the porous structure of the alumina plugs. As a result, severe densification was observed inside the alumina plugs in contact with molten steel containing high oxygen levels. In comparison, no densification occurred in the plugs contacting with the steel having low oxygen contents of 51 and 2.5 ppm. [ABSTRACT FROM AUTHOR]

To assess the viability of an alumina-chromia refractory alternative for secondary copper smelters, the degradation behavior of alumina-chromia refractories in a secondary copper smelting slag and a Cu-Cu x O mixture was studied via lab scale refractory finger testing. Microstructural characterization of the worn refractory samples resulted in a comprehensive understanding of the corrosion and penetration resistance and a comparison with the degradation of magnesia-chromite refractories. Alumina grains in the refractory are preferentially corroded by the slag. The alumina-chromia refractory exhibits superior infiltration resistance to the slag and the Cu-Cu x O mixture compared to magnesia-chromite refractories. [ABSTRACT FROM AUTHOR]

The effect of surfactant Te on the behavior of alumina inclusions at advancing solid-liquid interfaces of liquid steel was studied by adding Te to liquid steel before Al deoxidation at 1873 K. After water-quenching, the spatial distribution homogeneity of alumina inclusions in the steel matrix was characterized using the Dirichlet tessellation method. The deterioration of this homogeneity with increasing the addition of Te indicates that Te facilitates pushing of alumina inclusions. This phenomenon was discussed based on the thermodynamics of an asymmetric thin liquid film confined by an advancing solid-liquid interface and a particle. The surface excesses of Te at the solid-liquid and particle-liquid interfaces were theoretically demonstrated to decrease when an alumina inclusion moves towards the solid-liquid interface, thereby weakening the effect of Te on the solid-liquid and particle-liquid interfacial energies. Based on this, effect of surfactants was incorporated in the models predicting the critical velocity V C . [ABSTRACT FROM AUTHOR]

The corrosion behavior of alumina-silica (Al 2 O 3 –SiO 2 ) refractories by liquid carbon steel was studied. This was performed by a refractory crucible test in a vacuum induction furnace at 1520–1545 °C under reducing atmosphere. The results indicate that Mn, Si and a minor amount of Fe in the steel were oxidized at steel/refractory interface, combing with refractory components to form a MnO–SiO 2 –Al 2 O 3 –based slag. This slag was liquid at the testing temperature, and infiltrated along the open-pore network and the grain boundaries into the Al 2 O 3 –SiO 2 refractories. Both Al 2 O 3 –rich and Al 2 O 3 –SiO 2 aggregates in the refractories dissolved into the infiltrating slag. As a result, the refractories were structurally weakened and residual Al 2 O 3 –rich and Al 2 O 3 –SiO 2 aggregates in the hot face of the refractories were washed away into the liquid steel, affecting steel quality. [ABSTRACT FROM AUTHOR]