Mass Pct Al2O3 Research Articles

Crystallization Behavior, Viscosity and Structure of CaO–SiO2–MgO–(15~30 Mass Pct) Al2O3 Melts Representing the Oxide Inclusions in Si-Killed Steel

Crystallization Behavior, Viscosity and Structure of CaO–SiO2–MgO–(15~30 Mass Pct) Al2O3 Melts Representing the Oxide Inclusions in Si-Killed Steel

Roles of MgO and Al2O3 in Viscous and Structural Behavior of Blast Furnace Primary Slag with C/S = 1.4

Permeability is crucial for stable operation and strengthening of smelting in blast furnace ironmaking, especially for the current utilization of low-grade iron ore. The viscosity of the primary slag is an important factor affecting permeability. In this study, the roles of MgO and Al2O3 in the viscous and structural behavior of CaO-MgO-Al2O3-SiO2-10 mass pct FeO (CaO/SiO2 weight ratio of 1.4) primary slag were investigated. The results showed that slag viscosity initially decreased and subsequently increased when Al2O3 content was increased from 6 to 16 mass pct, having the lowest value at 10 mass pct Al2O3. The reduction in viscosity with increase in Al2O3 content from 6 to 10 mass pct was attributed to the effect of solid crystals dissolving into the liquid phase caused by the decrease in the liquidus temperature, while the increase in viscosity at higher Al2O3 contents up to 16 mass pct was caused by the network-forming role of Al2O3 owing to its acidic nature. The viscosity fluctuated with increase in MgO content from 6 to 16 mass pct, which was related to the variation in the equilibrated primary phase field. The MgO and Al2O3 in the molten slag network structure functioned as network modifier and network former, respectively, to change the silicate network, as verified by Fourier transform infrared (FTIR) and Raman spectroscopy.

Evolution of Oxide Inclusions in Si-Mn-Killed Steel During Protective Atmosphere Electroslag Remelting

The current study was motivated to reveal the evolution of MnO-SiO2-Al2O3 inclusions during protective atmosphere electroslag remelting (P-ESR), and the effect of slag composition on the inclusion evolution. The oxide inclusions in the consumable steel electrode were ternary (7.1-26.4 mass pct) MnO-(53.3-82.8 mass pct) SiO2-(8.3-23.1 mass pct) Al2O3 without exception, which were fully removed during the P-ESR in two ways: a portion of these inclusions were dissociated in its individual chemical species into liquid steel, whereas the others were removed by absorbing them into molten slag before liquid metal droplets collected in liquid metal pool during P-ESR. The oxide inclusions both in liquid metal pool and in remelted ingots are mostly MgAl2O4 (containing about 3 mass pct MgO) and Al2O3 inclusions, irrespective of the SiO2 contents (1.9 to 9.0 mass pct) in the slag. These inclusions readily formed in the liquid metal pool as a result of the reaction between alloying elements and the dissolved oxygen in liquid steel that dissociated from MnO-SiO2-Al2O3 inclusions.

Activity of MnO in MnO-CaO-SiO2-Al2O3-MgO Molten Slags

The activities of MnO in the MnO-CaO-SiO2-Al2O3 (10, 20, and 30 mass pct)-MgO (5 mass pct) melts at 1873 K (1600 °C) were measured by equilibrating the melts with liquid copper under an oxygen partial pressure controlled by CO/CO2 gas mixture with a volume ratio of 99/1. Over the investigated composition range, MnO shows a negative deviation from Raoultian behavior. On the basis of the experimental data, the activity coefficient of MnO in this multicomponent melts was evaluated using the following quadratic formalism based on regular solution model: \( RT\ln {\gamma_{{\text{MnO}}({\text{s}})}} = \sum\limits_j {{\alpha_{ij}}x_j^2} + \sum\limits_j {\sum\limits_k {( {{\alpha_{ij}} + {\alpha_{ik}} - {\alpha_{jk}}}){x_j}{x_k} + I{^\prime}} } . \) The values of the conversion factor, I′, for the melts containing 10, 20, and 30 mass pct Al2O3 were determined to be 6950, 2715, and 12092 J/mol, respectively. Iso-activity contours for MnO in the five component system were calculated using the quadratic formalism, and they showed a good agreement with the experimental data.

Effects of MgO/Al2O3 Ratio and Basicity on the Viscosities of CaO-MgO-SiO2-Al2O3 Slags: Experiments and Modeling

The effects of the MgO/Al2O3 ratio and basicity on the viscosities of CaO-MgO-SiO2-Al2O3 slags were investigated at 1733 K, 1773 K, and 1823 K (1460 °C, 1500 °C, and 1550 °C) in this study. At a fixed Al2O3 of 15 and 18 mass pct, increasing the basicity from 1 to 1.2 resulted in lowering the viscosity of slags. At a fixed basicity of 1.0 and 1.2, increasing the MgO from 0 to 15 mass pct decreased the viscosity of slags. The Fourier transform-infrared spectra analysis of the slag structure was made to discuss the depolymerization roles of MgO and basicity. Considering the different depolymerization effects of basic oxides upon the silicate/aluminate network structure as suggested by FT-IT analysis, a fresh model for predicting the viscosity of CaO-MgO-SiO2-Al2O3 slags was constructed. A total of 209 viscosity measurements with large compositional variations showed satisfactory agreement with the results calculated by the present model. With the aid of the current model, the co-effects of the MgO/Al2O3 ratio and basicity on the viscosities of CaO-MgO-SiO2-Al2O3 slags (15 to 20 mass pct Al2O3) were investigated.

In-Situ Study of Gaseous Reduction of Magnetite Doped with Alumina Using High-Temperature XRD Analysis

The reduction of magnetite of technical grade and magnetite doped with 3 mass pct Al2O3 was studied in situ using high-temperature XRD (HT-XRD) analysis. Magnetite was reduced by CO-CO2 gas (80 vol pct CO) at 1023 K (750 °C). Reduction of magnetite doped with alumina occurred from the Fe3O4-FeAl2O4 solid solution which has a miscibility gap with critical temperature of 1133 K (860 °C). The degree of reduction of magnetite was derived using Rietveld refinement of the HT-XRD spectra; the compositions of the Fe3O4-FeAl2O4 solid solution and the concentrations of carbon in γ-iron were determined from the lattice constants of the solutions. The reduction of magnetite progressed topochemically with the formation of a dense iron shell. The reduction of alumina-containing magnetite started along certain lattice planes with the formation of a network-like structure. Reduction of alumina-containing magnetite was faster than that of un-doped magnetite; this difference was attributed to the formation of the network-like structure. Hercynite content in the Fe3O4-FeAl2O4 solid solution in the process of reduction of magnetite doped with 3 mass pct Al2O3 increased from 5.11 to 20 mass pct, which is close to the miscibility gap at 1023 K (750 °C). The concentration of carbon in γ-Fe (0.76 mass pct) formed in the reduced sample of magnetite doped with 3 mass pct Al2O3 was close to the equilibrium value with 80 vol pct CO to 20 vol pct CO2 gas used in the HT-XRD experiments.

Thermodynamics of Gold Dissolution Behavior in CaO-SiO2-Al2O3-MgOsat Slag System

Gold solubility in the CaO-SiO2-Al2O3-MgOsat slag system was measured at 1773 K (1500 °C) under a CO2–CO atmosphere over a wide range of compositions, i.e., 8 to 40 mass pct CaO, 26 to 50 mass pct SiO2, and 0 to 36 mass pct Al2O3, to determine the dissolution mechanism of gold in the CaO-based metallurgical slags. Gold solubility in the present slag system increased with increasing oxygen partial pressure and increasing activity of CaO. From the thermodynamic analysis, the dissolution mechanism of gold into the (alumino-)silicate melts is proposed as follows according to the activity of basic oxide, which indicates that the predominant species of gold is dependent on slag basicity. $$ {\text{Au}}(s) + \frac{1}{4}{\text{O}}_{2} (g) + \frac{1}{2}\left( {{\text{O}}^{2 - } } \right) = \left( {{\text{AuO}}^{ - } } \right),\quad \left( {a_{\text{BO}} < 0.1} \right) $$ $$ {\text{Au}}(s) + \frac{1}{4}{\text{O}}_{2} (g) + \frac{3}{2}\left( {{\text{O}}^{2 - } } \right) = \left( {{\text{AuO}}_{2}^{3 - } } \right),\quad \left( {a_{\text{BO}} > 0.1} \right) $$ The enthalpy change for the dissolution of gold into the CaO-SiO2-Al2O3-MgOsat slag system was measured to be about −80 kJ/mol, indicating that the gold dissolution is exothermic. From the iso-Au solubility contours, the dominant factor affecting the gold dissolution behavior is the (CaO + MgO)/SiO2 ratio, whereas the influence of Al2O3 was negligible. Consequently, less basic slags and higher processing temperatures, in conjunction with a strongly reducing atmosphere, are recommended to increase gold recovery during pyro-processing of Au-containing e-wastes.

Effect of Alumina on the Gaseous Reduction of Magnetite in CO/CO2 Gas Mixtures

Reduction of magnetite doped with alumina (3, 6 and 12 mass pct Al2O3) was studied using CO/CO2 gas mixture (80 vol pct CO) at 1023 K and 1123 K (750 °C and 850 °C). The reduction rate and degree of reduction were evaluated from the weight loss of a sample with time. The reduction behavior was analyzed using the results of XRD and SEM–EDS measurements and thermodynamic analysis. Effect of alumina on the magnetite reduction depended on the alumina content and temperature. Magnetite reduction at 1023 K (750 °C) was accelerated by the addition of 3 mass pct Al2O3, however, the rate of reduction significantly decreased with the further increase in the alumina content to 6 and 12 mass pct. Different effect of alumina was observed in reduction at 1123 K (850 °C); the rate of reduction of the Fe3O4-Al2O3 mixture with 6 mass pct Al2O3 was the fastest. Reduction of un-doped magnetite was developed topochemically with the formation of a dense iron shell. However, reduction of alumina-doped magnetite to wustite started along certain lattice planes with the formation of network-like structure. In the course of reduction, Al3+ ions diffused from wustite to the Fe3O4-FeAl2O4 solution enriching hercynite content in the solution at the reaction interface. Further reduction of alumina-rich Fe3O4-FeAl2O4 solution resulted in the formation of micro-cracks which enhanced the rate of the reduction process.

Effect of Slag Composition on the Distribution Behavior of Pb between FetO-SiO2 (-CaO, Al2O3) Slag and Molten Copper

The distribution behavior of Pb between molten copper and FetO-SiO2 (-CaO, Al2O3) slags was investigated at 1473 K (1200 °C) and \( p_{{{\text{O}}_{2} }} = 10^{ - 10} \,{\text{atm}} \) in view of the reaction mechanism of Pb dissolution into the slag. Furthermore, the lead capacity of the slag was estimated from the experimental results. The distribution ratio of Pb (LPb) decreases with increasing CaO content (~6 mass pct) irrespective of Fe/SiO2 ratio (1.4 to 1.7). However, the addition of alumina into a slag with Fe/SiO2 = 1.5 linearly decreases the LPb, whereas a minimum value is observed at about 4 mass pct Al2O3 at Fe/SiO2 = 1.3. The log LPb continuously decreases with increasing Fe/SiO2 ratio, and the addition of Al2O3 (5 to 15 mass pct) into the silica-saturated iron silicate slag (Fe/SiO2 < 1.0) yields the highest Pb distribution ratio. This is mainly due to a decrease in the FeO activity even at silica saturation. The log LPb linearly decreases by increasing the log (Fe3+/Fe2+) value. The Pb distribution ratio increases and the excess free energy of PbO decreases with increasing Cu2O content in the slag. However, from the viewpoint of copper loss into the slag, the silica-saturated system containing small amounts of alumina is strongly recommended to stabilize PbO in the slag phase at a low Cu2O content. The lead capacity was defined in the current study and shows a linear correlation with the activity of FeO in a logarithmic scale, indicating that the concept of lead capacity is a good measure of absorption ability of Pb in iron silicate slags, and the activity of FeO can be a good basicity index in iron silicate slag.

Experimental Investigation of the Viscosities of High Titanium Containing Slags with Low Mass Ratio of CaO to SiO&lt;sub&gt;2&lt;/sub&gt;

This present paper focuses on the viscosities of high titanium containing slags in the process of titanomagnetite smelting by taking the TiO2-Al2O3-CaO-SiO2 quaternary system as the object. Experimental determinations of the viscosities were carried out in the temperature range from 1573 to 1773K using the rotation cylinder method. The measurements were conducted in the composition range from 23 to 33 mass pct TiO2, 3 to 9 mass pct Al2O3, and 0.3 to 0.7 basicity (mass ratio of CaO to SiO2). The effects of TiO2, Al2O3, basicity, and temperature on viscosity were studied. The experimental results indicated that the viscosities decreased with increasing TiO2 content and basicity, and increased with increasing Al2O3 content, above the liquidus temperature. Based on the experimental data, the liquidus temperatures of the slags were evaluated using the second derivatives of the activation energies for viscous flow with respect to temperature.

Experimental Determination of the Liquidus in the High-Basicity Region in the Al2O3(25 mass pct)-CaO-MgO-SiO2 and Al2O3(35 mass pct)-CaO-MgO-SiO2 Systems

Liquidus in the Al2O3(25 mass pct)-CaO-MgO-SiO2(<20 mass pct) and Al2O3(35 mass pct)-CaO-MgO-SiO2(<20 mass pct) systems were determined experimentally in the high-CaO-containing region at 1873 K (1600 °C). For the Al2O3(35 mass pct)-CaO-MgO-SiO2(<20 mass pct) system, liquidus data were also determined for 1773 K (1500 °C). The equilibrating and quenching technique with subsequent electron probe microanalyzer (EPMA) microanalysis were employed. Based on the data, liquidus lines were constructed for the 25 and 35 mass pct alumina planes at silica contents generally below 20 mass pct. The current results showed a slightly lower solubility of CaO and a higher solubility of MgO at 1873 K (1600 °C) for the 25 mass pct Al2O3 section compared with the existing phase diagram. At 1773 K (1500 °C), the result showed a slightly lower solubility of both CaO and MgO in the 35 mass pct Al2O3 section compared with the existing phase diagram. In addition, the activities of MgO, CaO, and Al2O3 were estimated at 1773 K and 1873 K (1500 °C and 1600 °C) using the phase diagram information.

Amphoteric behavior of alumina in viscous flow and structure of CaO-SiO2 (-MgO)-Al2O3 slags

The viscosity of CaO-SiO2 (-MgO)-Al2O3 slags was measured to clarify the effects of Al2O3 and MgO on the structure and viscous flow of molten slags at high temperatures. Furthermore, the infrared spectra of the quenched slags were analyzed to understand the structural role of Al2O3 in the polymerization or depolymerization of silicate network. The Al2O3 behaves as an amphoteric oxide with the composition of slags; that is, the alumina behaves as a network former up to about 10 mass pct Al2O3, while it acts as a network modifier, in parts, in the composition greater than 10 mass pct Al2O3. This amphoteric role of Al2O3 in the viscous flow of molten slags at the Newtonian flow region was diminished by the coexistence of MgO. The effect of Al2O3 on the viscosity increase can be understood based on an increase in the degree of polymerization (DOP) by the incorporation of the [AlO4]-tetrahedra into the [SiO4]-tetrahedral units, and this was confirmed by the infrared (IR) spectra of the quenched slags. The influence of alumina on the viscosity decrease can be explained on the basis of a decrease in the DOP by the increase in the relative fraction of the [AlO6]-octahedral units. The relative intensity of the IR bands for the [SiO4]-tetrahedra with low NBO/Si decreased, while that of the IR bands for [SiO4]-tetrahedra with high NBO/Si increased with increasing Al2O3 content greater than the critical point, i.e., about 10 mass pct in the present systems. The variations of the activity coefficient of slag components with composition indirectly supported those of viscosity and structure of the aluminosilicate melts.

An experimental study of the viscosities of Al2O3-CaO-“FeO” slags

Experimental determinations of the viscosities of some Al2O3-CaO-“FeO” ternary slags were carried out in the temperature range from 1550 to 1764 K using the rotation cylinder method. The measurements were conducted in the composition range from 36 to 48 mass pct Al2O3, 28 to 42 mass pct CaO, and 10 to 33 mass pct FeO. The viscosity was found to show a decreasing trend with the increase of FeO content. Based on the experimental data, the liquidus temperatures of the slags were evaluated using the second derivatives of the activation energies for viscous flow with respect to temperature. The evaluated liquids temperatures were compared with the results of differential thermal analysis (DTA) on the same slag samples.

Activities of SiO2 and Al2O3 and activity coefficients of FetO and MnO in CaO-SiO2-Al2O3-MgO slags

The activities of SiO2 and Al2O3 in CaO-SiO2-Al2O3-MgO slags were determined at 1873 K along the liquidus lines saturated with 2CaO · SiO2, 2(Mg,Ca)O · SiO2, MgO, and MgO · Al2O3 phases using a slag-metal equilibration technique. Based on these and previous results obtained in ternary and quaternary slags, the isoactivity lines of SiO2 and Al2O3 over the liquid region on the 0, 10, 20, 30, and 40 mass pct Al2O3 planes and those on the 10 and 20 mass pct MgO planes were determined. The activity coefficients of FetO and MnO, the phase boundary, and the solubility of MgO were also determined.