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

• 作者: Igor S. Yakimov Sergei D. Kirik Yulia N. Zaitseva
• 来源期刊: 金属学报(美国)
• 学科: 化学
• 关键词: Aluminum Production ELECTROLYTE COMPOSITION Ternary System NaF-AlF3-CaF2 XRD ELECTROLYTE COMPOSITION CONTROL
• 年，卷（期）: jsxbmg_2013,（4）
• 页码范围: 86-91
• 页数: 6页
• 分类号: O6

摘要

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.