CaO SiO2 CaF2 Research Articles

Electrochemical Behavior of Si(IV) and the Preparation of WSi2 Alloys in Molten CaO–SiO2–CaF2

Electrochemical Behavior of Si(IV) and the Preparation of WSi2 Alloys in Molten CaO–SiO2–CaF2

Quantitative Characterization of Reaction Behavior between La‐Bearing FeCrAl Melt and CaO–SiO2‐Based Slags

The reaction behavior between La‐bearing FeCrAl melt and CaO–SiO2‐based slags is quantitatively characterized based on industrial sampling, slag‐steel reaction simulation experiment, mass balance calculation, and thermodynamic theoretical analysis. In the results, it is shown that compared with FeCrAl melt, [La] in La‐bearing FeCrAl melt not only reacts with SiO2 in slags, but also promotes the reaction of [Al] with SiO2 and Na2O. The percentage of mass change of [La] after reaction with CaO–SiO2–Na2O–Al2O3 and CaO–SiO2–CaF2–Al2O3 slag is the highest increased by 92.43 wt%, and that of [Al] is the highest increased by 4.68 wt%. The percentages of mass change of SiO2, Na2O, and Al2O3 are the highest increased by 9.48, 2.91, and 52.86 wt%, respectively. Thermodynamic analysis shows that in FeCrAl melt, La not only increases the activity of itself, but also enhances the activity of Al to a certain extent, which is conducive to increasing the reaction degree between [Al] and Na2O and SiO2 in CaO–SiO2‐based slags. Moreover, the reaction behavior of CaO–SiO2–Na2O–Al2O3 and CaO–SiO2–CaF2–Al2O3 slags is compared and the main reasons are analyzed. The results of slag‐steel reaction simulation experiment are consistent with the trend of composition change of the mold flux in industrial sampling.

Sulfide Capacity and Activity of Iron Oxide in CaO–SiO<sub>2</sub>–FeO Ternary System at 1573 K

The knowledge of sulfide capacities of FeO-containing slags is necessary for better understanding the resulfurization reaction in hot metal pre-treatments. In this study, copper-iron-sulfur liquid alloy was equilibrated with CaO–SiO2–FeO ternary slag to measure sulfide capacities and FeO activities simultaneously at temperature below the melting point of pure iron. The experimental result that the sulfide capacity increased with increasing FeO content could be explained by the fact that FeO was a basic oxide, and the sulfide capacity of the CaO–SiO2–FeO ternary system was significantly larger than those of the CaO–SiO2–MgO, CaO–SiO2–AlO1.5 and CaO–SiO2–CaF2 ternary systems. Although the FeO activity and oxygen potential were raised by the FeO addition, the calculated value for sulfur distribution ratio between CaO–SiO2–FeO slag and hot metal increased with an increase in FeO content.

Selective separation and crystal characterization of RE‐phases from RE‐bearing slag systems: Calcium cerite and cefluosil

AbstractThe industrial RE‐bearing (rare‐earth‐bearing) slag has a considerable concentration of rare‐earth elements (REEs), so the recovery of REEs resources from these systems has attracted widespread attention. However, the basic data of RE phases is seriously lacked and divergent, which greatly limits the efficient utilization. In this study, in situ separation of RE phases from RE‐bearing slag systems was conducted via super gravity, and the high‐purity crystals of calcium cerite (CaO: 13.53 wt.%, SiO2: 26.02 wt.%, Ce2O3: 65.45 wt.%) and cefluosil (CaO: 14.67 wt.%, SiO2: 22.14 wt.%, CaF2: 2.64 wt.%, Ce2O3: 67.23 wt.%) were selectively separated from the CaO–SiO2–Ce2O3 and CaO–SiO2–CaF2–Ce2O3 systems with the high REEs recovery percentages of 96.10% and 98.23%, respectively. Based on the characterization of high‐purity calcium cerite and cefluosil crystals, the chemical formula, crystal structure, and Rietveld refinement were characterized, and the data has been assigned the deposition numbers of 2130965 and 2142394 in CCDC database. This study supplements the lack of basic data of RE crystals and provides theoretical reference and guidance for the utilization of RE‐bearing slag systems.

Comprehensive Understanding of the Role of Carbon Black in the Sintering and Melting Behavior of Mold Flux

Carbon materials play an important role in controlling the sintering and melting behaviors of mold flux. However, the reactions between carbon and mold fluxes and corresponding effects on the properties of mold fluxes are ignored in previous studies. The effects of carbon black on the sintering and melting behavior of mold flux during the heating process were systematically investigated by TG-FTIR, DSC, XRD, TEM, SEM, XPS, Raman spectroscopy, and viscosity measurement. The results showed that: carbon black between the mineral particles was visualized by TEM, and Ca4Si2O7F2 as sintering phase was not formed until 1300°C in CaO–SiO2–CaF2–Na2O slag on account of the insulation of carbon black. Residual carbon black absorbed on the surface of slag droplets suppressed the melting by preventing the aggregation of droplets. Besides, SiC as production of the carbon-slag reaction significantly increased the slag viscosity by improving the polymerization degree of molten slag.

Experimental investigation on SMAW electrode coatings developed using CaO–SiO2–CaF2–SrO based coating system

This research aims to provide a SMAW electrode coating developed using a CaO–SiO2–CaF2–SrO flux system for welding the components of an advanced ultra-supercritical power plant. The physicochemical and thermophysical characteristics of developed coatings were investigated. Twenty-one distinct electrode coating formulations were developed using the extreme vertices technique. Experiments for several thermophysical and physicochemical characteristics were carried out. The coating's qualities are critical for producing a strong weld that will last in the field. X-ray diffraction and Infrared spectroscopy were used to examine the structural behavior of the electrode coatings. Furthermore, the regression model was developed to explore the effect of coating compositions. The primary constituents and their interaction have an influential role in physicochemical and thermophysical characteristics. Individual and ternary mixtures significantly affect the density. CaO.SiO2.SrO and CaF2·SiO2·SrO is the most effective ternary mixture, which has an increasing effect on density. The weight loss of coating observed during thermogravimetric analysis is affected by individual constituents significantly. The ternary mixture CaO·CaF2·SiO2, CaO·CaF2·SrO, and CaF2·SiO2·SrO is the most favorable and has an increasing effect on weight loss. Individual constituents affect change in enthalpy significantly. The thermal properties of coating observed during hot disc are affected by binary and ternary mixture constituents. Binary mixture CaO·SiO2 is having an increasing effect on thermal conductivity. Binary mixture CaO·SrO and SrO containing ternary mixture have an increasing impact on thermal diffusivity. Ternary mixture constituents CaO·CaF2·SrO, CaF2·SiO2·SrO is the most effective and has an increasing effect on specific heat.

In situ separation and characterization of britholite crystals in RE‐bearing slag via supergravity

AbstractBayan Obo ore has abundant rare earth (RE) reserves, and RE elements (REEs) are mainly transferred into the RE‐bearing slag. However, the utilization of RE‐bearing slag is greatly limited due to the serious lack and ambiguity of RE crystals. In this study, in situ separation of RE crystals from RE‐bearing slag via supergravity was developed, and the high‐purity crystals of britholite with various REEs contents were selectively separated from the CaO–SiO2–CaF2–P2O5–Ce2O3 system with a high REEs recovery ratio of 95.58%–98.65%. On this basis, the chemical formula, the crystal structure, and the formation mechanism of britholite were characterized from the high‐purity crystals through a combination of the Rietveld refinement and DFT calculation. It was found that the britholite was verified to be evolved from Ca5(PO4)3F, there would be an SiO44− instead of a PO43− when a Ce3+ replaced a Ca2+, the chemical formula changed from Ca5(PO4)3F to Ca4.377Ce0.623Si0.6P2.4O12F, Ca3.956Ce1.044Si1.01P1.99O12F, and Ca3.176Ce1.824Si1.93P1.07O12F with the increase of REEs content, and the substitution range of REEs was between 0 and 2. This study supplements some necessary basic data of RE crystals, which provides the theoretical reference for efficient recovery of RE resources and sustainable utilization of RE‐bearing slag.

The relationship between melt structure and viscosity: the effect of different fluxes on CaO–SiO2 slags

Abstract Na2O, CaF2, B2O3 are commonly used fluxes in metallurgical slags. These fluxes reduce the viscosity of slags are related to changing the melt structures. In this study, molecular dynamics simulation was used to analyze the main effects of Na2O, CaF2, and B2O3 respectively on the melt structure of the traditional CaO–SiO2 metallurgical slags. The results showed that since Na+ ions have only one charge, and the electrostatic restraint between the multi-charged ions and the depolymerized [SiO4]4− tetrahedrons cannot occur on Na+ ions. The overall mobility of the particles in the melt structure is improved with the replacement of Ca2+ with Na+. Therefore, the fluidity of CaO–SiO2–Na2O slags is stronger than that of CaO–SiO2, and the viscosity is reduced. F− ions mainly bond with Ca2+ ions to form complexes. The resulting Ca–F structures destroy the electrostatic restraint between Ca2+ ions and depolymerized depolymerized [SiO4]4− tetrahedrons in the Ca–O structures, and the fluidity of CaO–SiO2–CaF2 slags are improved. The effect of B2O3 on the melt structure of CaO–SiO2 is related to the basicity. In this study, when the value of basicity is 1.87, the addition of B2O3 increases the degree of polymerization of the CaO–SiO2 melt structure, and the viscosity may increases.

Viscosity of RE-bearing slag systems and kinetics of nucleation and growth for RE-phases

The RE-bearing slag with a considerable concentration of rare earths have attracted widespread attention in recent years, while the serious lack of basic data greatly limits its development and utilization. The viscosity of RE-bearing slag and kinetics for nucleation and growth of RE-phase are basic data which closely related to the mass transfer, separation and recovery of rare earths in the slag. However, the current reports on viscosity of RE-bearing slags are extremely scanty, and the existing viscosity models also have limitations due to the lack of thermodynamic data of rare earths. In this study, the viscosities of various RE-bearing slag systems (CaO–SiO2–Ce2O3, CaO–SiO2–CaF2–Ce2O3 and CaO–SiO2–CaF2–P2O5–Ce2O3) were firstly measured by the rotating cylinder method, and the change rules of viscosity for RE-bearing slag with CaF2 and P2O5 were reported. Moreover, the nucleation and growth kinetics of various RE-phases (calcium cerite, cefluosil, and britholite) were comprehensively studied, and the crystallization ability of RE-phases in RE-bearing slag was found to be cefluosil, followed by britholite and calcium cerite. The basic data reported in this study provide the necessary reference and guidance for recovery and utilization of rare earths in RE-bearing slag.

Investigation in CaO–SiO2–CaF2–C slags during the sintering and melting process

ABSTRACT The reaction behaviour and mechanism of carbon and mould fluxes during the heating process were deeply considered through TG-FTIR, XRD, DSC, and SEM techniques. The results showed that: there were four main stages of weight loss for slags during heating process. One hundred to 300 °C and 300–500°C were the volatilization of free water and bound water, respectively. Five hundred to 800°C was the decomposition process of carbonate. However, at 800–1400°C, CaO–SiO2–CaF2 slag was the reaction of slag component themselves. CaO–SiO2–CaF2–C series slags were the reaction behaviour between carbon and slags (C and Ca2SiO4, Ca4Si2O7F2). The DSC and SEM analysis illustrated that the solid phase reaction temperature range of CaO–SiO2–CaF2–C being 1320–1370°C was larger than that of CaO–SiO2–CaF2 being 1070–1250°C. Additionally, CaO–SiO2–CaF2 slag was completely molten at 1400°C, while CaO–SiO2–CaF2–C did not, suggesting that the sintering and melting process were suppressed by carbon.

Structure and crystallization of glassy La2O3–CaO–SiO2–CaF2 system rare-earth slag with variable rare-earth content

Raman spectroscopy and differential scanning calorimetry were employed to investigate the structure, crystallization behavior and crystallization activation energy of the La2O3–CaO–SiO2–CaF2 (RE) slags with different RE contents. Raman spectroscopy analysis indicated that the RE oxide, La2O3, acted as a network modifier, with the increase in La2O3 content decreasing the degree of polymerization of the RE slag. As the La2O3 content increased, the number of highly polymerized Q2 and Q3 species gradually decreased, while the minimally polymerized Q0 and Q1 species increased, and depolymerizing the complex network structure in the slag. The slag mainly contained the following three crystal phases: (Ca, La)5(SiO4)6F, CaSiO3, and Ca4Si2O7F2. When the La2O3 content increased to 15%, an additional Ca2SiO2F2 crystalline phase appeared. Furthermore, an increase in the La2O3 content from 10 to 17% reduced the crystallization temperature of the RE phase in the slag from 1641 to 1599K. The crystallization behavior of the RE phase under different cooling rates revealed that the increase in La2O3 content reduced the effective crystallization activation energy of the RE phase, thus enhancing the crystallization of the RE phase. Thus, a correlation between the structure and crystallization of the RE slag was established.

Effect of Li2O on Non-Isothermal Crystallization of Cuspidine in CaO–SiO2–CaF2 Glasses

Effect of Li2O on Non-Isothermal Crystallization of Cuspidine in CaO–SiO2–CaF2 Glasses

Qualitative, Quantitative and Mechanism Research of Volatiles in the Most Commonly Used CaO–SiO2–CaF2–Na2Ο Slag During Casting Process

Qualitative, Quantitative and Mechanism Research of Volatiles in the Most Commonly Used CaO–SiO2–CaF2–Na2Ο Slag During Casting Process

Phase equilibria of CaO–SiO2–CaF2–P2O5–Ce2O3 system and formation mechanism of britholite

Recently, the sustainable utilization of REE-bearing slag for the recovery and application of rare-earth elements (REEs) has attracted considerable attention. However, a limited amount of thermodynamic data and crystal information for REE systems has been reported, which greatly limits the utilization of REE-bearing slag. In this study, the isothermal phase diagram of the CaO–SiO2–CaF2(30 wt%)-P2O5(10 wt%)-Ce2O3 system was constructed to provide phase equilibria data for the REEs in REE-bearing slag. The formation mechanism of britholite (Ca5-xCex[(Si,P)O4]3F) in the quinary system was found: it evolved from Ca5(PO4)3F, when a Ce3+ replaced a Ca2+, there would be a SiO44− instead of a PO43−. The phase equilibria and formation mechanism of REEs in the CaO–SiO2–CaF2–P2O5–Ce2O3 system are supplied to provide the data required for sustainable utilization of REE-bearing slag.

Effect of Li2O on melt crystallization of CaO–SiO2–CaF2 based glasses

This paper presents the effects of Li2O on the kinetics and structural aspects of the Cuspidine (Ca4Si2F2O7) crystallization behavior of CaO–SiO2–CaF2 glass (basicity 1.7). In order to elucidate the crystallization characteristics during differential scanning calorimetry (DSC) measurements, the kinetic parameters have been determined using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. The crystallization rate constant and negative activation energy thus calculated indicated that the limiting step of crystallization was nucleation. Also, Raman spectroscopy and Solid-state MAS NMR spectroscopy analyses indicated that lithium could interact with fluorine, thereby disturbing the interaction between calcium and fluorine. This retards Cuspidine nucleation at the initial stage of melt crystallization. These findings on CaO–SiO2–CaF2-based glass lubricants can be used to optimize essential properties such as viscosity and crystallization temperature during continuous casting of steels.

Thermodynamics and kinetics of REEs in CaO–SiO2–CaF2–Ce2O3 system: A theoretical basis toward sustainable utilization of REEs in REE-Bearing slag

Sustainable utilization of rare earth elements (REEs) in REE-bearing slag has recently attracted significant interest in industries and research community. However, few thermodynamic and kinetic data have been reported for REEs systems, which greatly limits the sustainable utilization of REE-bearing slag in ceramics and other fields. Therefore, the isothermal phase diagram of CaO–SiO2–CaF2–Ce2O3 system was constructed, and the phase equlibria data of REEs in REE-bearing slag were provided in this study. On this basis, the phase equilibria of the RE-phase in CaO–SiO2–CaF2–Ce2O3 system was investigated, the exact initial crystallization temperature of cefluosil (Ce9.33-xCax(SiO4)4O5-0.5xF2) in the system was 1450 K and the cefluosil crystals were in a hollow hexagonal prism shape. The isothermal crystallization and growth kinetics of cefluosil were further studied. The crystallization kinetics of cefluosil were found to be described by the Johnson-Mehl-Avrami-Kolmogoro (JMAK) equation (when χ < 1), and the growth of cefluosil in the non-equilibrium stage is controlled by the coarsening energy. In this research, the thermodynamic and kinetic data of REEs in CaO–SiO2–CaF2–Ce2O3 system are supplied, which providing the theoretical basis for sustainable utilization of REEs in REE-bearing slag.

Effect of Fluorine on Melt Structure for CaO–SiO&lt;sub&gt;2&lt;/sub&gt;–CaF&lt;sub&gt;2&lt;/sub&gt; and CaO–Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;–CaF&lt;sub&gt;2&lt;/sub&gt; by Molecular Dynamics Simulations

The melt structure with fluorine addition has been investigated using molecular dynamics (MD) simulation for the CaO–SiO2–CaF2 and CaO–Al2O3–CaF2 ternary slag system. By analyzing the coordination number of the network framework, the results indicate that the structure of Si–O tetrahedron is more stable than the structure of Al–O tetrahedron. F− ions are dominantly coordinated with Ca2+, there is a dynamic equilibrium between Ca2+ and the coordination anions (O2− and F−) in both systems, and the total coordination number (CN) is maintained between 6 and 7. The analysis of the distribution of oxygen types demonstrates the degree of polymerization (DOP) of network structure in CaO–SiO2–CaF2 system is lower than that in CaO–Al2O3–CaF2 system. Although the addition of CaF2 can lower the viscosity of both slag systems, the microscopic reasons for that are completely different: in CaO–SiO2–CaF2 system, CaF2 actually acts as network diluent, and creates the space where particles can move longer. But in CaO–Al2O3–CaF2 system, CaF2 can depolymerize the network structure of the melt.

Determination of Viscosity and Surface Tension for CaO–SiO2–CaF2 Slags

Determination of the physicochemical properties of solutions is important for industrial applications. Geometrical models, specifically the “mass triangle model” and a new model, have been utilized to calculate the viscosity and surface tension of CaO–SiO2–CaF2 slags based on the corresponding ternary system boundary data within the partially soluble region. The two models are validated with available experimental data in terms of viscosity and surface tension. Results reveal that the models are capable of estimating the physicochemical properties of the ternary system with limited solubility with high accuracy. The new model predicts the viscosity better, but the mass triangle model may perform better for the surface tension predictions. It is expected that these two solution models could be applied to the calculation of physicochemical properties of more ternary systems with limited solubility, especially when the systems are with high melting points or/and volatile components and/or easily oxidized or reduced components.

In situ observations of isothermal cuspidine crystallization in molten mould fluxes with varying basicity

ABSTRACT Cuspidine is an important crystallization product in CaO–SiO2–CaF2 based mould flux. A deeper understanding of cuspidine crystallization behaviour is significant to obtain superior heat transfer and lubricative properties. Cuspidine crystallization was observed in situ using a confocal scanning laser microscopy. The results shown that cuspidine typically shows different dendritic morphologies in molten fluxes. The morphology transforms from long equiaxed dendrites, partially equiaxed dendrites and small block shape containing dendrites concurrence to regular blocky shapes containing dendrites as the isothermal temperature decreases from 1150°C to 1000°C for a flux with R = 1.1. Cuspidine morphology changes from robust dendrites, partially dendrites and small block shapes containing dendrites concurrence to blocky shapes containing dendrites as the isothermal temperature decreases from 1250°C to 1150°C for a flux with R = 1.2. The effects of temperature and basicity on the morphology transition and growth of cuspidine were analysed.

Design & development of SAW fluxes using CaO–SiO2–CaF2 and CaO–SiO2–Al2O3 flux systems

Physicochemical and thermo-physical behaviour were studied for the agglomerated submerged arc fluxes for CaO–SiO2–CaF2 and CaO–SiO2–Al2O3 flux system. Mixture design approach was used to develop twenty-one fluxes. Thermogravimetric (TGA), differential-scanning calorimetric (DSC), hot-disk technique and XRD techniques were utilized to analyse the fluxes. Structural behaviour of fluxes was analyzed using Fourier transform infrared spectrometer. Thermal behaviour of fluxes was observed in the temperature range of 25 °C to 900 °C. Thermo-physical behaviour such as specific heat, thermal diffusivity and thermal conductivity of each flux were evaluated by hot disc technique. Multi objective optimization was performed to derive the optimized flux formulations. This type of flux formulation helps us to evaluate the physical-chemical and thermo-physical behaviour of different mineral constituents used during submerged arc welding process.