Probing Molten Salt Flux Reactions Using Time-Resolved in Situ High-Temperature Powder X-ray Diffraction:  A New Synthesis Route to the Mixed-Valence NaTi₂O₄

Abstract

A new molten salt synthesis route to the mixed-valence sodium titanate NaTi 2 O 4 has been discovered. Reduction of Na 8 Ti 5 O 14 by Ti metal powder in a 3:1 molar mixture of NaCl:KCl at 770°C produced crystals of NaTi 2 O 4 . Use of the molten salt flux lowered the synthesis temperature of this compound by over 400°C. Time-resolved in situ high-temperature X-ray powder diffraction was used to probe the kinetics and mechanism of the reaction. Energydispersive X-ray diffraction (EDXRD) data revealed that the reaction is rapid; the phase begins to form in 30 min at 770°C, and product formation is essentially complete within 2 h. Crystalline solids are present in the molten salt flux at all times during the course of the reaction, indicating that the mechanism most likely involves reactions occurring at the surfaces of the solid particles, mediated by the molten salt flux. Possible key intermediates identified through EDXRD and quenching studies are Ti 3 O, Na 2 Ti 6 O 13 , and Na 0.54 TiO 2 . This new molten salt synthesis route offers a facile way to reproducibly prepare large samples of this mixed-valence compound for further study.

Ambient-Pressure Synthesis of Two New Vanadium-Based Calcium Ferrite-Type Compounds: NaV1.25Ti0.75O4 and NaVSnO4

“…This is reminiscent of, e.g., the NaCl−KCl eutectics that were used to obtain NaTi 2 O 4 from Na 8 Ti 5 O 14 and Ti at moderate temperatures. 18 Further improvements in synthesis methodology are needed to obtain phase-pure samples, but these results demonstrate that CaFe 2 O 4 -type compounds can be obtained using the relatively benign conditions used here. The crystal structure of 1 and 2 contains double chains of edge-sharing MO 6 octahedra.…”

“…Difficult synthetic conditions (1200°C and a resistance furnace) are also used to get NaTi 2 O 4 from Na metal and TiO 2 , 16,17 although small crystals of NaTi 2 O 4 were obtained from Na 8 Ti 5 O 14 and Ti at 770°C using a KCl/ NaCl flux. 18 Overall, the relatively soft conditions used here to obtain 1 and 2 are of interest. It has recently been demonstrated that Na + in NaV 2 O 4 becomes mobile above 250 K, offering possible application in electrochemical energy devices.…”

Blue/Red Linear Dichroic Emission from a Highly Anisotropic Crystal of Triarylmethane Dye Conjugated with Phenoxo‐Zinc Complexes

“…Of course, all of these methods require constant optimization as well as real‐time, in‐process monitoring. In the latter context, time‐resolved in situ high‐temperature X‐ray diffraction has been used recently to probe the kinetics and mechanism of a molten‐salt synthesis route towards the production of mixed‐valence sodium titanate, suggesting that the reaction occurred at the surfaces of the solid particles mediated by the molten‐salt flux 187…”

Molten salt synthesis of zinc aluminate powder

“…It has been used to synthesise low melting electroceramic powders 14 and high temperature complex oxide powders (e.g., MgAl 2 O 4 ). 15 The purpose of this work is to use MSS for the preparation of ZnAl 2 O 4 powder by heating equimolar ZnO and Al 2 O 3 powders in alkaline chlorides (LiCl, NaCl or KCl).…”