TITLE:
Thermal Transformations in the System NaF-CaF2-AlF3 and X-Ray Diffraction Control of Ca-Containing Electrolytes for Aluminum Production
AUTHORS:
Yulia N. Zaitseva, Igor S. Yakimov, Sergei D. Kirik
KEYWORDS:
Aluminum Production; Electrolyte Composition; Ternary System NaF-AlF3-CaF2; XRD Electrolyte Composition Control
JOURNAL NAME:
Open Journal of Metal,
Vol.3 No.4,
December
16,
2013
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.