On the influence of humidity on the mechanochemical reaction between NaF and AlF3

Followed by 19F and 27Al MAS NMR and XRD measurements the present study unambiguously addresses the distinct influence of humidity on the product composition in the mechanochemical reaction of NaF with AlF3. The water content, either delivered from the educts or controlled by the gaseous atmosphere, plays a crucial role for the reactions investigated here. Generally, the mechanically induced chemical reactions are favoured under wet conditions. They do not proceed stoichiometrically yielding mixtures of at least two components: Na5Al3F14 and AlF3, or Na5Al3F14 and Na3AlF6. However, applying the molar ratio Na:Al = 1:1 and using NaF and β-AlF3·3H2O as educts, several hours of milling surprisingly forms the thermodynamically unstable phase NaAlF4·H2O.

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