Aluminium phosphate behaviour in Na3AlF6–Al2O3 melts: a new insight from in situ high temperature NMR measurements

Abstract

The effects of aluminium phosphate dissolution on speciation in Na₃AlF₆–Al₂O₃ melts was studied. The structural description was performed via multinuclear (¹⁷O, ¹⁹F, ²³Na, ²⁷Al, and ³¹P) NMR measurements in situ at high temperature (HT) in melts of the Na₃AlF₆–Al₂O₃–AlPO₄ system. Consistent with our previous findings, the PO₄³⁻, AlF₅²⁻, Al₂OF₆²⁻, Al₂O₂F₄²⁻, and (AlF₄–O–PO₃)⁴⁻ anions are present in the melt. When AlPO₄ is introduced in the melt containing alumina, the formation of Al–O–P linkages become more favorable compared with the system without alumina.