Fluoroacidity evaluation in molten salts

Anne-Laure Bieber (1) , Laurent Massot (1) , Mathieu Gibilaro (1) , Laurent Cassayre (1) , Pierre Chamelot (1) , Pierre Taxil (1)

1 LGC - Laboratoire de Génie Chimique

The fluoroacidity of several alkaline fluoride media was studied by monitoring the concentration of electroactive species which is decreasing versus time due to a gas species release, such as silicon fluorides, as indicated by the reaction: SiF(4+x)x- = SiF4(g) + x F- This article relates the Si(IV) reaction study to define a relative fluoroacidity scale by studying the silicon ions stability in different melts. Electrochemical techniques allow the measurement of SiF4+xx- concentration evolution and thus the reaction rate constant to be calculated at different temperatures and for several fluoride media. The article shows that the free F- content depends on the fluoride mixture and that the rate values are correlated with the fluoroacidity allowing a qualitative estimation. Then a fluoride solvents fluoroacidity scale was proposed, scaling the different eutectic melts from basic melt to acidic one: NaF-KF < LiF-KF < NaF-MgF2 < NaF-CaF2 < LiF-NaF < LiF < LiF-CaF2.

Mots clés: Fluoroacidity; Molten fluorides; Silicon ions; Electrochemistry

Domaines: Génie chimique

Anne-Laure Bieber, Laurent Massot, Mathieu Gibilaro, Laurent Cassayre, Pierre Chamelot, et al.. Fluoroacidity evaluation in molten salts. Electrochimica Acta, 2011, vol. 56, pp. 5022-5027. ⟨10.1016/j.electacta.2011.03.099⟩. ⟨hal-00813237⟩