Thermal transformation of quaternary compounds in NaF–CaF2–AlF3 system

Zaitseva, Julia N.; Yakimov, Igor S.; Кирик, С. Д.

doi:10.1016/j.jssc.2009.05.043

Cited by 17 publications

(10 citation statements)

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“…As can be observed, it is a simple eutectic system without solid solubility. 14 The liquidus and solidus lines experimentally determined by Fedotieff and Iljinsky 18 and calculated by Beilmann et al 8 are also shown. Beilmann et al 8 used classical polynomial as well as modified quasi-chemical models to determine the solidus and liquidus planes, which provided eutectic composition of 68.6 mol % and 67.2 mol % NaF in CaF 2 , respectively.…”

Section: ■ Results and Discussionmentioning

confidence: 57%

“…10−12 Molten NaF−AlF 3 −CaF 2 is the base solvent for alumina in Hall−Heŕoult electrolysis cells for primary aluminum production. 13,14 The physical and chemical proper- hydrogen contents. 11,12,15 For example, the removal of sulfurcontaining species from molten metal by CaO-based slags is a well-known, effective, and inexpensive process for sulfur capture.…”

Section: ■ Introductionmentioning

confidence: 99%

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Phase Equilibria Evaluation for CO₂ Capture: CaO–CaF₂–NaF, CaCO₃–NaF–CaF₂, and Na₂CO₃–CaF₂–NaF

et al. 2014

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This paper presents partial phase relations for the systems NaF–CaF2, NaF–CaF2–CaO, NaF–CaF2–CaCO3, NaF–CaF2–NaCO3, and NaF–CaF2–Na2CO3–CaCO3. The data were obtained by thermal analysis (TA), thermodynamic calculations (FactSage), and X-ray diffraction (XRD) of quenched samples. There was particular emphasis on revealing the phase formations of CaO, CaCO3, and Na2CO3 in the eutectic composition of NaF–CaF2 for the development of a novel carbon capture technology. Therefore, a thermal analysis of the binary CaF2–NaF system was performed first. A eutectic point was found at 31.9 mol % CaF2 and 814.8 °C. The liquidus isotherms and phase regions of the Na–Ca//F–O and Na–Ca//F–CO3 systems were mapped using FactSage. In addition, some compositions in the NaF–CaF2–CaO and NaF–CaF2–Na2CO3–CaCO3 systems were studied by TA. XRD analysis of the quenched samples was applied for phase identification. Based on the FactSage simulation and the experimental data, the solubility of CaO increases with increasing CaF2 concentration in NaF melt. It was derived that carbonates (Na2CO3 and CaCO3) in NaF–CaF2 are present as intermediate compounds. The reactions of NaF and CaCO3 and the formation of complex carbonates are discussed. In general, there is good agreement between experimental data and simulations.

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Section: ■ Results and Discussionmentioning

confidence: 57%

Section: ■ Introductionmentioning

confidence: 99%

Phase Equilibria Evaluation for CO₂ Capture: CaO–CaF₂–NaF, CaCO₃–NaF–CaF₂, and Na₂CO₃–CaF₂–NaF

et al. 2014

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“…). This fact is apparently the consequence of the nonequilibrium crystallization process, during which NaCaAlF 6 incompletely converts into Na 2 Ca 3 Al 2 F 14 and exists in a metastable state at temperatures below 500°C …”

Section: Combined X‐ray Diffraction–x‐ray Fluorescence Analysis Of Bamentioning

confidence: 99%

“…This fact is apparently the consequence of the nonequilibrium crystallization process, during which NaCaAlF 6 incompletely converts into Na 2 Ca 3 Al 2 F 14 and exists in a metastable state at temperatures below 500°C. [7] Thus, alternative approach to quantifying Ca-containing phases is needed when CR is measured by calibrated XRD method. As both CaF 2 and Na 2 Ca 3 Al 2 F 14 have clear diffraction peaks and can be accurately quantified via calibration curves, their concentrations must be used in this case.…”

Section: Introductionmentioning

confidence: 99%

Combined control of aluminum bath composition by X‐ray diffraction and X‐ray fluorescence analysis

et al. 2017

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The present paper provides a combined application of X-ray diffraction (XRD) and X-ray fluorescence (XRF) methods in process control for the analysis of aluminum baths of different compositions. Developed approaches to the combined calibration XRD and XRF methods, independent calibration XRF techniques and to the full-profile automated Rietveld analysis of a bath composition are described.We established that combined XRD-XRF calibration techniques provide an accurate stable analysis of technological parameters in a wide range of traditional and low-melting compositions due to an accurate quantification of CaF 2 , MgF 2 and KF additives. The developed XRF techniques provide quantitative analysis of both cryolite ratio and alumina with the accuracy of 0.03 and 0.25% wt. respectively, which is comparable with the technologically required accuracy.The evolutionary approach that automates full profile quantitative XRD analysis of bath composition and uses XRF data on Ca and Mg provides a better accuracy of measuring cryolite ratio compared to an accuracy of non-automated analysis by Rietveld method.Combined application of the two X-ray methods eliminates gross analytical errors and stabilizes overall performance of a smelter's process control system.

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“…Calcium fluoride combined with the excess of aluminum fluoride is the most widely used additive for decreasing the operation temperature in an electrolysis bath in aluminum production [1]. The additives significantly influence the electrolysis efficiency, however its concentrations considerably change in the course of electrolysis due to the high temperature and volatility of the electrolyte components [2]. Therefore, the technology of aluminum production implies monitoring the bath composition and applies to periodical electrolyte correction.…”

Section: Introductionmentioning

confidence: 99%

Thermal Transformations in the System NaF-CaF<sub>2</sub>-AlF<sub>3</sub> and X-Ray Diffraction Control of Ca-Containing Electrolytes for Aluminum Production

Zaitseva¹,

Yakimov²,

Кирик³

2013

OJMetal

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The details of ternary fluoride crystallization in the system NaF-CaF 2-AlF 3 have been specified. The phases NaCaAlF 6 , Na 2 Ca 3 Al 2 F 14 and NaAlF 4 have been obtained by high-temperature synthesis. Their thermal transformations have been studied using high-temperature X-ray diffraction. The occurring transformations can be considered in a quasibinary system CaF 2-NaAlF 4 , where at T = 745˚C-750˚C invariant equilibrium is established with the phases CaF 2-NaCaAlF 6-Na 2 Ca 3 Al 2 F 14-(NaAlF 4). The compounds NaCaAlF 6 and Na 2 Ca 3 Al 2 F 14 are stable in different temperature ranges. The phase NaCaAlF 6 was fixed by rapid quenching from the melt. It decomposes at heating before 640˚C yielding Na 2 Ca 3 Al 2 F 14 and NaAlF 4. Direct and inverse transformations between NaCaAlF 6 and Na 2 Ca 3 Al 2 F 14 occur in the bulk samples of the electrolyte. A thermal treatment procedure was proposed for the solid electrolyte sample to get a sample corresponding to the composition of the melt and providing high phase crystallinity for the purposes of quantitative X-ray phase diffraction analysis.

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Thermal transformation of quaternary compounds in NaF–CaF2–AlF3 system

Cited by 17 publications

References 10 publications

Phase Equilibria Evaluation for CO₂ Capture: CaO–CaF₂–NaF, CaCO₃–NaF–CaF₂, and Na₂CO₃–CaF₂–NaF

Phase Equilibria Evaluation for CO₂ Capture: CaO–CaF₂–NaF, CaCO₃–NaF–CaF₂, and Na₂CO₃–CaF₂–NaF

Combined control of aluminum bath composition by X‐ray diffraction and X‐ray fluorescence analysis

Thermal Transformations in the System NaF-CaF<sub>2</sub>-AlF<sub>3</sub> and X-Ray Diffraction Control of Ca-Containing Electrolytes for Aluminum Production

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Thermal transformation of quaternary compounds in NaF–CaF2–AlF3 system

Cited by 17 publications

References 10 publications

Phase Equilibria Evaluation for CO2 Capture: CaO–CaF2–NaF, CaCO3–NaF–CaF2, and Na2CO3–CaF2–NaF

Phase Equilibria Evaluation for CO2 Capture: CaO–CaF2–NaF, CaCO3–NaF–CaF2, and Na2CO3–CaF2–NaF

Combined control of aluminum bath composition by X‐ray diffraction and X‐ray fluorescence analysis

Thermal Transformations in the System NaF-CaF&lt;sub&gt;2&lt;/sub&gt;-AlF&lt;sub&gt;3&lt;/sub&gt; and X-Ray Diffraction Control of Ca-Containing Electrolytes for Aluminum Production

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Phase Equilibria Evaluation for CO₂ Capture: CaO–CaF₂–NaF, CaCO₃–NaF–CaF₂, and Na₂CO₃–CaF₂–NaF

Phase Equilibria Evaluation for CO₂ Capture: CaO–CaF₂–NaF, CaCO₃–NaF–CaF₂, and Na₂CO₃–CaF₂–NaF

Thermal Transformations in the System NaF-CaF<sub>2</sub>-AlF<sub>3</sub> and X-Ray Diffraction Control of Ca-Containing Electrolytes for Aluminum Production