The Melt of Sodium Nitrate as a Medium for the Synthesis of Fluorides

Abstract

The preparation of NaLnF 4 complexes, LnF 3 (Ln = La, Ce, Y) rare earth binary fluorides, CaF 2 and SrF 2 alkali earth fluorides, as well as mixtures of these compounds from their nitrates dissolved in molten NaNO 3 has been studied in order to select the ideal solvent for fluoride synthesis by spontaneous crystallization from flux. Sodium fluoride (NaF) was used as a fluorinating agent. The results of our experiments have confirmed that NaNO 3 melt is one of the most promising media for precipitating said inorganic fluoride materials within a broad temperature range (300-500 • C). Also, in contrast with precipitation/co-precipitation from aqueous solutions, our syntheses have resulted in obtaining equilibrium phases only.

Low‐temperature phase formation in the SrF2–LaF3 system

“…It seems that individual fluorides are formed first in nitrate melts of complex composition during fluorination, and then their interaction occurs in the melt of alkaline element nitrate. A similar situation was observed in the previous work 40 for the CaF 2 -SrF 2 system at a low synthesis temperature of 300°C.…”

“…Promising for the synthesis of fluoride systems is nitrate fluxes, namely melts of alkali metal nitrates, primarily sodium nitrate. [40][41][42][43] NaNO 3 melts at 308°C, stable up to 500° C. The melting point can be lowered by adding potassium or lithium nitrates. [44][45][46] The purpose of this work is to study the low-temperature phase formation in the SrF 2 -LaF 3 system using a nitrate flux, to find out the limits of the stability of the non-stoichiometric phases.…”

“…The flux has to satisfy a number of requirements, 40 including the solubility of the flux components in the test substance must be negligible. Promising for the synthesis of fluoride systems is nitrate fluxes, namely melts of alkali metal nitrates, primarily sodium nitrate 40‐43 . NaNO 3 melts at 308°C, stable up to 500° C. The melting point can be lowered by adding potassium or lithium nitrates 44‐46 …”

Synthesis of NaYF4:Yb, Er up-conversion luminophore from nitrate flux

“…Among the various methods of synthesis, much attention is drawn to the first melt-solution method proposed by Batsanova [18,38,44], which consists in the reaction of REE nitrates with sodium fluoride, which acts as a fluorinating agent. As a flux, low-melting sodium nitrate is used.…”

Nanotechnology and material science

“…Very long equilibrium times, in many cases, make experimental studies impossible [12]. The use of molten salt synthesitic techniques allows ones to significantly expand the temperature range available to the study [13,14]. It is worth noting that, according to the third law of thermodynamics, all solid solutions are non-stable phases at low temperatures [12].…”