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Viscosity of the Molten Mixtures FLiNaK-LnF3 (Ln = La, Ce, Nd).

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Title: Viscosity of the Molten Mixtures FLiNaK-LnF3 (Ln = La, Ce, Nd).
Authors: Tkacheva, O.1 (AUTHOR) o.tkacheva@ihte.ru, Rudenko, A.1 (AUTHOR)
Source: International Journal of Thermophysics. Dec2025, Vol. 46 Issue 12, p1-15. 15p.
Subjects: Viscosity, Viscometry, Ionic solutions, Rheology, Rare earth metals, Fused salts
Abstract: Molten salt eutectic FLiNaK containing lanthanide fluorides (LnF3) is widely used in various industrial applications and research projects, so knowledge of the physicochemical properties of such complex ionic melts is crucial. The dynamic viscosity of the FLiNaK-LnF3 (Ln = La, Ce, Nd) molten salt mixtures with content of LnF3 3, 7 and 15 mol% was studied by rotational viscometry using rheometer FRS 1600 (Anton Paar). Viscosity measurements were carried out in the temperature range from 1023 K to a temperature close to the liquidus of each composition. The viscosity of the FLiNaK-LnF3 melts increases significantly both with decreasing temperature and with increasing LnF3 content. The viscosity values of molten mixtures with the same content of LaF3, NdF3 or CeF3 do not differ insignificantly. However, a tendency for a more substantial decrease in viscosity is observed when introducing the LnF3 additives in the sequence CeF3 > NdF3 > LaF3. This tendency is violated for the dependence of viscosity on the superheating temperature (20, 100, 200 degrees above the liquidus): the viscosity of molten mixtures with any lanthanide fluoride in an amount greater than 7 mol% does not change. For the FLiNaK-NdF3 melts, the dependence of the fluidity on the molar volume was determined using the available data on the density of these melts. The fluidity of the FLiNaK-NdF3 decreases with increasing NdF3 concentration. However, when comparing the fluidity values versus the relative molar volume, it turns out that it stops changing in melts with an NdF3 content of more than 7 mol%. Such a change in the viscosity and fluidity of FLiNaK-LnF3 melts is explained by their complex ionic structure. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:Molten salt eutectic FLiNaK containing lanthanide fluorides (LnF3) is widely used in various industrial applications and research projects, so knowledge of the physicochemical properties of such complex ionic melts is crucial. The dynamic viscosity of the FLiNaK-LnF3 (Ln = La, Ce, Nd) molten salt mixtures with content of LnF3 3, 7 and 15 mol% was studied by rotational viscometry using rheometer FRS 1600 (Anton Paar). Viscosity measurements were carried out in the temperature range from 1023 K to a temperature close to the liquidus of each composition. The viscosity of the FLiNaK-LnF3 melts increases significantly both with decreasing temperature and with increasing LnF3 content. The viscosity values of molten mixtures with the same content of LaF3, NdF3 or CeF3 do not differ insignificantly. However, a tendency for a more substantial decrease in viscosity is observed when introducing the LnF3 additives in the sequence CeF3 > NdF3 > LaF3. This tendency is violated for the dependence of viscosity on the superheating temperature (20, 100, 200 degrees above the liquidus): the viscosity of molten mixtures with any lanthanide fluoride in an amount greater than 7 mol% does not change. For the FLiNaK-NdF3 melts, the dependence of the fluidity on the molar volume was determined using the available data on the density of these melts. The fluidity of the FLiNaK-NdF3 decreases with increasing NdF3 concentration. However, when comparing the fluidity values versus the relative molar volume, it turns out that it stops changing in melts with an NdF3 content of more than 7 mol%. Such a change in the viscosity and fluidity of FLiNaK-LnF3 melts is explained by their complex ionic structure. [ABSTRACT FROM AUTHOR]
ISSN:0195928X
DOI:10.1007/s10765-025-03658-7