Phase diagram assessment of CaO–Al2O3–La2O3 system

Considering the significance of CaO–Al₂O₃–RE₂O₃ (RE?=?rare earth) phase diagrams, the Redlich–Kister expression was employed to evaluate the binary phase diagrams of CaO–Al₂O₃, La₂O₃–Al₂O₃ and CaO–La₂O₃ systems in the present work. Also, the activities of CaO and Al₂O₃ in the CaO–Al₂O₃ binary system were calculated. The phase diagram of the CaO–Al₂O₃–La₂O₃ ternary system was first assessed by Kohler extrapolation method. The accuracy of calculated phase diagrams was validated by comparing with existing experimental points and the calculation results from the literature. The obtained diagrams will lay a foundation for Al-killed steelmaking process, metallurgical flux and other fields’ industrial application.     

Kinetics of Na2O evaporation from CaO–Al2O3–SiO2–MgO–TiO2–Na2O slags

The present work is carried out to study the evaporation of Na₂O from CaO–Al₂O₃–SiO₂–TiO₂–MgO–Na₂O slags with high basicity and high alumina in the temperature range of 1500–1560°C. The ratio of evaporation was determined by monitoring the Na₂O content change of the slag melt under isothermal reduction conditions. The results show that the evaporation ratio increases with increasing the temperature. Higher basicity and increasing concentrations of Na₂O, Al₂O₃ are also found to increase the evaporation ratio of Na₂O, while MgO addition only slightly enhances the evaporation ratio. With TiO₂ content increasing, the evaporation ratio first increases and then decreases. The evaporation rate of Na₂O appears to be controlled by chemical reaction at the slag/gas interface in the beginning, followed by a mixed reaction-mass transfer regime, and finally a liquid-phase mass transport step. The apparent activation energy is 134.74?kJ?mol^?1 for the chemical reaction regime and 268.53?kJ?mol^?1 for the liquid-phase mass diffusion step.     

Properties investigation of CaO–Al2O3–SiO2–Li2O–B2O3–Ce2O3 mould flux with different w(CaO)/w(Al2O3) for heat-resistant steel continuous casting

The new CaO–Al₂O₃–SiO₂–Li₂O–B₂O₃–Ce₂O₃ mould flux was devised to realise smooth continuous casting of Ce-bearing heat-resistant steel. The new devised mould flux was based on calcium-aluminate system, so the w(CaO)/w(Al₂O₃) has great influence on the properties of the slag, which is similar to the basicity in the silicate system. The melting temperature, viscous properties, slag structure and crystalline phases with different w(CaO)/w(Al₂O₃) were investigated. The melting temperature of the mould flux could remain relatively steady with w(CaO)/w(Al₂O₃) in the range of 1.0–1.82. The main network former in the new slag was [AlO₄]-tetrahedron. The network formed by [AlO₄]-tetrahedron was destroyed by increasing w(CaO)/w(Al₂O₃), the viscosity decreased consequently. The mould flux show weaker crystallisation tendency with increasing w(CaO)/w(Al₂O₃). When the temperature decreased to 1100°C, the change of the fully crystallised phases with increasing w(CaO)/w(Al₂O₃) was as follows: Li₂O·Al₂O_3?+?2CaO·Al₂O₃·SiO_2?→?Li₂O·Al₂O_3?→?Li₂O·Al₂O_3?+?3CaO·Al₂O_3?+?CaCeAlO₄.     

Dissolution rate of Al2O3 into molten CaO–Al2O3–CaF2 flux

Abstract

Dissolution of Al₂O₃ into molten CaO–Al₂O₃–CaF₂, a base system of mould flux for continuous casting of high Al steel, has been investigated by employing a rotating cylinder method. The dissolution rate of an alumina rod into molten CaO–Al₂O₃–CaF₂ flux increased with increase in rotating speed and temperature. The apparent activation energy for mass transport of flux C was calculated to be 255·6 kJ mol^?1. The rate controlling step during the dissolution process of the alumina rod into molten CaO–Al₂O₃–CaF₂ flux was found to be the diffusion of the solute in the flux boundary layer. The dissolution rate of alumina into molten CaO–Al₂O₃–CaF₂ flux increased with increasing CaO/Al₂O₃, and it may be caused by the increase in thermodynamic driving force and the decrease in the viscosity of the flux. When the Al₂O₃ rod was immersed into molten flux, an intermediate compound of CaO.2Al₂O₃ formed firstly and then dissolved into molten flux.     

Density of Na3AlF6–AlF3–LiF–MgF2–Al2O3–Sm2O3 molten salt melt for Al–Sm alloy

Samarium (Sm) has been widely used in making aluminum (Al)–Sm magnet alloy materials. The research team for this study developed a molten salt electrolyte system which directly produces Al–Sm alloy to replace the energy intensive conventional distillation technology. In this study, molten melt density was measured and operation conditions were optimized to separate Al–Sm alloy product from the fluoride molten melt electrolysis media based on density differences. Archimedes' principle was applied to measure density for the basic molten fluoride system (BMFS: Na₃AlF₆–AlF₃–LiF–MgF₂) electrolysis media in the temperature range from 905 to 1055 °C. The impact of temperature (t) and the Al₂O₃ and Sm₂O₃ addition ratio (w_(Al2O3), w_(Sm2O3)) in the basic fluoride system on molten melt density was examined. The fluoride molten melt density relationship was determined to be: ρ = 3.11701 ? 0.00802w_(Al2O3) + 0.027825w_(Sm2O3) ? 0.00117t. The test results showed that molten density decreases with increase in temperature and Al₂O₃ addition ratio, and increases with the addition of Sm₂O₃, and/or Al₂O₃ + Sm₂O_3. The separation of Al–Sm (density 2.3 g/cm³) product melt from the BMFS melt is achieved by controlling the BMFS density to less than 2.0 g/cm³. It is concluded that the optimal operation conditions to control the BMFS molten salt density to less than 2.0 g/cm³ are: maintain addition of Al₂O₃ + Sm₂O₃ (w_(Al2O3) + w_(Sm2O3)) < 9% of Na₃AlF₆, Al₂O₃/Sm₂O₃ ratio (w_(Al2O3):w_(Sm2O3)) > 7:3, and temperature between 965 and 995 °C.     

Phase Equilibria in the ZrO2–La2O3–Gd2O3 System at 1600°C

Powder Metallurgy and Metal Ceramics - Phase equilibria and structural transformations in the ternary ZrO2–La2O3–Gd2O3 system at 1600°C were studied by X-ray diffraction,...     

Effect of Heat Treatment on the Physicochemical Properties of Ultrafine ZrO2–Y2O3–CeO2–Al2O3–CoO Powders

Powder Metallurgy and Metal Ceramics - Variations in the phase composition, specific surface area, and morphology of structural components in the ultrafine powder of composition (wt.%) 70 (90 ZrO2...     

High-temperature phase equilibria of Cu–O–Al2O3 system in air

Phase equilibria of Cu–O–Al₂O₃ system were experimentally investigated in a temperature range of 1100–1400°C under 0.21?atm oxygen pressure. The experiments were conducted employing a high-temperature equilibration and quenching method. Microstructures of the quenched samples were observed with scanning electron microscope. The phase compositions in the samples were analysed with electron probe microanalysis technique. Measured solubility of Al₂O₃ into the molten oxide ranged from 0.0 to 1.8?wt-%. A small solubility of Cu₂O into Al₂O₃ was also observed ranging from 1.20 to 1.58?wt-%.     

The Influence of the ZrO2 Solid Solution Amount on the Physicochemical Properties of Al2O3–ZrO2–Y2O3–CeO2 Powders

Powder Metallurgy and Metal Ceramics - Alumina-based nanocrystalline powders with different ZrO2 amounts were produced for the first time by hydrothermal synthesis in an alkaline environment for...     

Viscosity of CaO–MgO–Al2O3–SiO2 melts containing SiC particles

The influence of SiC particle on viscosity of CaO–MgO–Al₂O₃–SiO₂ melts was investigated by the rotating-cylinder method. It was found that temperature dependence of viscosity could be described by the Arrhenius law for systems with or without SiC particle addition. The activation energies of liquid–solid mixtures were mainly determined by liquid phase. Temperature had little influence on the relative viscosity (defined as the viscosity ratio of solid–liquid mixture to pure liquid). Viscosity and relative viscosity increased as decreasing rotation speed and increasing volume fraction of SiC solid particle. For the same volume fraction of SiC particle, relative viscosity was affected by the liquid slag compositions. The relative viscosity was smaller when composition of liquid slag had a larger CaO/SiO₂ ratio or MgO/Al₂O₃ ratio. Meanwhile, it was found that the smaller SiC particle will lead to a larger relative viscosity.     

Viscosity of low silica CaO–5MgO–Al2O3–SiO2 slags

Abstract

The viscosity of CaO–5MgO–Al₂O₃–SiO₂ slag with low silica was measured by rotating cylinder method up to 1823 K. Slag compositions were chosen based on five different levels of SiO₂ content between 0 and 11·80%. The MgO content was 5·0%. The mass ratio of CaO/Al₂O₃ was varied from 0·66 to 1·95. It was shown that viscosity decreased with increasing temperature and decreased with increasing the mass ratio of CaO/Al₂O₃, following by an increase with further increasing the mass ratio of CaO/Al₂O₃. The viscosity decreased with the NBO/T ratio increasing, and the trend that flow activation energy changes with the NBO/T ratio of slag was the same as the trend that viscosity changes with the NBO/T ratio. Based on the experimental data as the boundary of the homogenous phase region, the mass triangle model was used to calculate the viscosity of low silica region.     

Changes in the Properties of Ultrafine Al2O3–ZrO2–Y2O3–CeO2 Powders After Heat Treatment in the Range 400–1450°C

Powder Metallurgy and Metal Ceramics - Ultrafine 90AZK, 80AZK, 70AZK, and 58.5AZK powders in the Al2O3–ZrO2–Y2O3–CeO2 system were produced for the first time by a combined method...     

Effect of Na2O on Viscosity,Structure and Crystallization of CaF2–CaO–Al2O3–MgO–TiO2 Slag in Electroslag Remelting

Russian Journal of Non-Ferrous Metals - The effect of Na2O on the viscosity, structure, and crystallization behavior of CaF2–CaO–Al2O3–MgO–TiO2 slag was studied using the...     

����������La2O3-Al2O3-CaF2����������Ũ��ģ��

In order to accurately control the rare earth content in liquid steel in electroslag remelting (ESR) process, according to the ion and molecule coexistence theory (IMCT) of slag structure and corresponding phase diagrams, a thermodynamic calculating model for the evaluation of mass action concentrations (designated by Ni for structure unit i) for La2O3-Al2O3-CaF2 slag system was formulated. The results show that the calculated values of NLa2O3 are in good agreement with the reported measured values, indicating that this calculating model can wholly embody the characteristics of the slag system. The activity of La2O3 decreases with the increasing of the Al2O3 and CaF2 content, and Al2O3 is stronger than CaF2 in decreasing the activity of La2O3. But the activity of La2O3 increase with the increasing in temperature at the composition range of 30% La2O3, 20% Al2O3, 50% CaF2. Above all, the activity of La2O3 in La2O3-Al2O3-CaF2 slag system can be quantitatively analyzed by this thermodynamic model, and this model can provide a theoretical basis for precisely controlling the lanthanum content in molten steel in ESR process.     

Evaluation of B2O3 as replacement for CaF2 in CaO–Al2O3 based mould flux

In order to develop low fluoride or fluoride free CaO–Al₂O₃ based mould flux for casting high aluminium steel, an investigation was carried out to study the effect of substituting CaF₂ with B₂O₃ on heat transfer and crystallisation behaviour of CaO–Al₂O₃ based mould flux by employing a heat transfer simulator of mould flux and a single hot thermocouple technique. The results showed that addition of CaF₂ promoted heat transfer of CaO–Al₂O₃ based mould flux, which was opposite to the effect of CaF₂ on heat transfer in conventional CaO–SiO₂ based mould flux. Addition of CaF₂ inhibited crystallisation of CaO–Al₂O₃ based mould flux by lowering the start crystallisation temperature and prolonging the incubation time of crystallisation. B₂O₃ showed similar effects to CaF₂ on heat transfer and crystallisation of CaO–Al₂O₃ based mould flux, but its ability to promote heat transfer and suppress crystallisation was stronger than CaF₂. Ca₃B₂O₆ (melting temperature 1480°C) was found as the primary crystalline phase in fluoride free CaO–Al₂O₃ based mould flux compared with the primary crystalline phase Ca₂Al₃O₆F (melting temperature 1507°C) in fluoride bearing (20% CaF₂) CaO–Al₂O₃ based mould flux.     

Processing and performance of Cr2O3–Fe2O3 reference electrode powders prepared by oxide coprecipitation

Abstract

Cr₂O₃–Fe₂O₃ based oxide mixtures for reference electrode powders of oxygen sensors were processed using oxide coprecipitation route. A special method for preparing reference electrode powders has been developed by mixing coarse Cr particles with the oxide mixture in the form of Cr–Fe hydroxide. Morphology and size of the mixed oxide powders were characterised by means of scanning electron microscopy and laser diffraction method. With the coprecipitation process, chemically homogeneous and very fine powders with a mean particle size of 1.53 μm were prepared. This powder mixture adhered and loosely coated to Cr particles. The processed reference electrode powders were tested in low level oxygen concentration measurements of steelmaking process under industrial scale. The reference electrode powders showed excellent results in terms of electromotive force reproducibility, response time and accuracy in soluble aluminium predictions at the oxygen concentration measurements. Most of the particles of the reference electrode powder remained separated after dipping to molten steel.     

CAS-OB refining: slag modification with B2O3–CaO and CaF2–CaO

Abstract

Evaluation of CAS-OB refining slags showed that the melting temperature and viscosity were very high and could further increase during the CAS-OB refining process, causing excessive slag to stick to the snorkel with resulting operational problems. To avoid this, B₂O₃–CaO (mass ratio 1 : 1) and CaF₂–CaO (mass ratio 1 : 1) were employed as modifiers added to the slag. The fusibility (melting temperature and viscosity) and desulphurising capacity of modified slag were investigated. Both B₂O₃–CaO and CaF₂–CaO can effectively lower the melting temperature and viscosity of slag. The results of experiments on sulphur partition equilibrium between metal and slag indicate that the sulphur content of metal can be further decreased by the modified slag.