Solubility of calcium and strontium fluorides in a sodium nitrate melt and choosing a crucible material for working with their solution melts

Irina I. Buchinskaya; Victoria Al. Ivchenko

doi:10.17308/kcmf.2023.25/10971

Irina I. Buchinskaya Shubnikov Institute of Crystallography, Crystallography and Photonics Federal Research Center, Russian Academy of Sciences, 59 Leninskii prospect, Moscow 119333, Russian Federation https://orcid.org/0000-0002-4658-5695
Victoria Al. Ivchenko Lomonosov Moscow State University, Faculty of Chemistry, 1-3 Leninskiye Gory, GSP-1, Moscow 119991, Russian Federation https://orcid.org/0000-0002-5821-2909

DOI: https://doi.org/10.17308/kcmf.2023.25/10971

Keywords: Calcium fluoride, Strontium fluoride, Sodium nitrate, Solubility, Solution melt, Powder X-ray diffraction analysis

Abstract

Sodium nitrate is a promising medium for the preparation of nanoparticles of some inorganic fluorides and for studying low-temperature phase equilibria in fluoride systems. In our study, we investigated the possibilities of carrying out longterm (hundreds of hours) experiments with МF₂–NaNO₃ (М = Ca, Sr).
We performed an experimental evaluation of the solubility of calcium (CaF₂) and strontium SrF₂ fluorides in a melt of sodium nitrate NaNO3 in the temperature range of 320–500 оС. The article demonstrates that for both fluorides it is low, but the solubility of SrF₂ is almost an order of magnitude higher than the solubility of CaF₂ and is about 1 g/100 g of NaNO₃ at 500 оС. The absence of perceptible oxidative processes and the low solubility of СaF₂ and SrF₂ fluorides in sodium nitrate make it possible to synthesize solid solutions based on them in this medium. The article also considers the possibility of using crucibles made of glazed ceramics, glass-carbon, and aluminium for working with МF₂–NaNO₃ (М = Ca, Sr) melt solutions. It is shown that glass-carbon and aluminium react with the NaNO₃–SrF₂ melt solution to form strontium carbonate
and several oxide phases, respectively.
It is recommended to use glazed ceramics as a crucible material for long-term solution-melt processes. The aluminium crucible showed high resistance to the NaNO₃ melt without dissolved fluorides.

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Author Biographies

Irina I. Buchinskaya, Shubnikov Institute of Crystallography, Crystallography and Photonics Federal Research Center, Russian Academy of Sciences, 59 Leninskii prospect, Moscow 119333, Russian Federation

Research Fellow at the
Laboratory of Growth Technologies, Synthesis and
Growth of Cr ystals, Shubnikov Institute of
Crystallography, Crystallography and Photonics
Federal Research Center, Russian Academy of Sciences
(Moscow, Russian Federation).

Victoria Al. Ivchenko, Lomonosov Moscow State University, Faculty of Chemistry, 1-3 Leninskiye Gory, GSP-1, Moscow 119991, Russian Federation

2nd year student of the
Faculty of Chemistry, Lomonosov Moscow State
University (Moscow, Russian Federation).

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