X-ray diffraction analysis of molten AlCl3–NaCl system

Abstract

The way in which structure of molten AlCl3–NaCl mixtures changes with AlCl3 concentration and temperature has been investigated by x-ray diffraction analysis. It was confirmed that AlCl4 tetrahedra are the fundamental structural units in the mixture of 50–70 mol % AlCl3. The nearest-neighbor distance of the Al–Cl, Na–Cl, and Cl–Cl pairs were 2.13, 2.80, and 3.48 Å, respectively. It was considered that the variation of the Q ⋅ i(Q) curves with AlCl3 concentration is due to the change of the mole ratio of AlCl−4 to Al2Cl−7 and the effect of the Na–Cl pair. It was supposed that AlCl−4 is tetrahedral and Al2Cl−7 is constructed from two corner-sharing AlCl4 tetrahedra. Both the concentration of Al2Cl−7 and the coordination number of Cl around an Na increased with increasing AlCl3 concentration at constant temperature, but decreased with increased temperature. The structure of the melt changed with variation of temperature at constant AlCl3 concentration.