Thermal Transformations in the System NaF-CaF₂-AlF₃ and X-Ray Diffraction Control of Ca-Containing Electrolytes for Aluminum Production

Yulia N. Zaitseva, Igor S. Yakimov, Sergei D. Kirik

Institute of Chemistry and Chemical Technology, SB RAS, Krasnoyarsk, Russia.
Siberian Federal University, Krasnoyarsk, Russia.

DOI: 10.4236/ojmetal.2013.34013                

Abstract

The details of ternary fluoride crystallization in the system NaF-CaF₂-AlF₃ have been specified. The phases NaCaAlF6, Na2Ca3Al2F14 and NaAlF4 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 CaF2-NaAlF4, where at T = 745°C - 750°C invariant equilibrium is established with the phases CaF₂-NaCaAlF₆-Na₂Ca₃Al₂F₁₄-(NaAlF₄). The compounds NaCaAlF₆ and Na₂Ca₃Al₂F₁₄ are stable in different temperature ranges. The phase NaCaAlF6 was fixed by rapid quenching from the melt. It decomposes at heating before 640°C yielding Na2Ca3Al2F14 and NaAlF4. Direct and inverse transformations between NaCaAlF6 and Na2Ca3Al2F14 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.

Keywords

Aluminum Production; Electrolyte Composition; Ternary System NaF-AlF₃-CaF₂; XRD Electrolyte Composition Control

Conflicts of Interest

The authors declare no conflicts of interest.

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