Multi‐nuclear magnetic resonance study of Na₃AlF₆AlPO₄ molten and solidified mixtures

Abstract

Phosphorus is one of the predominant impurities in the Hall-Heroult process for industrial aluminium production. The nature of the dissolved phosphorus species in the Na(3)AlF(6)-AlPO(4) system has been investigated by in situ high-temperature (HT) (19)F, (23)Na, (27)Al, (17)O, and (31)P NMR. The combination of these experiments enables to define the presence of PO(4)(3-), AlF(5)(2-) and (AlF(4)-O-PO(3))(4-) anions in the melt, and then the formation of Al-O-P bonding. Melts solidified at different cooling rates were characterised using various solid-state NMR techniques including multiple quantum magic angle spinning (MQMAS), rotational echo double resonance (REDOR) and heteronuclear single quantum correlation (HSQC). The glass obtained by the rapid quenching of the hypereutectic melt has been carefully described in order to better understand the structure of the melt.

Combined Approach for the Structural Characterization of Alkali Fluoroscandates: Solid-State NMR, Powder X-ray Diffraction, and Density Functional Theory Calculations

“…The structures of BaScO 2 F, Ba 2 ScO 3 F, and Sr 2 ScO 3 F contain only terminal fluorine atoms, and the 19 F chemical shift for these compounds were reported as −93, −79, and −113 ppm, respectively. The chemical shifts follow the same trend as those for bridging versus terminal fluorine atoms in fluoroaluminates; , i.e., the fluorine atoms giving rise to the signals at the lowest field are bridging, and the fluorine atoms resonating at high field are terminal. It should be noted that this statement is not fulfilled for all fluorine-containing systems.…”

Defects in Doped LaGaO3 Anionic Conductors: Linking NMR Spectral Features, Local Environments, and Defect Thermodynamics

“…The quadrupolar distribution associated with the structural disorder has been modeled by a Gaussian isotropic model − using an approach adopted for NMR of glasses and other disordered materials. ,, The method uses a probability density function (PDF) description of the strength (quadrupolar frequency ν Q ) and shape (asymmetry parameter η Q ) of the quadrupolar interaction tensor to characterize the MAS NMR line shape σ. The 2D MQMAS data and associated fitting of the Gaussian isotropic model line shape are presented in Figure b,c, from which a root-mean-square P Q of 1–2 MHz is obtained (Tables and S1), again in keeping with a disordered Mg VI coordination.…”

Solubility of AlPO4 and NaVO3 in NaF−AlF3 Melts

“…Because high-temperature 19 F NMR measurements excluded the presence of the P−F bond in the Na 3 AlF 6 −AlPO 4 molten system, it can be assumed that the change of the cryolite ratios to lower values did not influence the product of AlPO 4 dissolution in NaF−AlF 3 melts which should have been different phosphate anions.…”

“…Keppert et al presented a new approach to the structure of the Na 3 AlF 6 −AlPO 4 molten system. They measured in situ high-temperature NMR spectra using a wide range of different nuclei involved in the Na 3 AlF 6 −AlPO 4 system: 19 F, 27 Al, 23 Na, 31 P, and 17 O.…”