Densified micro-zone molten salt method for scale-up synthesis of high-entropy ceramic powders

Molten salt method has been widely used in synthesis of high-entropy ceramics powders, yet their scalable productions for industrial application are lacking. In this work, for the first time, a densified micro-zone molten salt (DMMS) approach was developed for scale-up preparation of high-entropy ceramic powders, including zirconates, hafnate, silicate and carbide. The “densified” block of DMMS permitted only the trace evaporation of molten salt on surfaces, and the internal “micro-zone” salt pools significantly promoted the in-situ formation of high-entropy phases at relatively low temperatures. Single-phase (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)₂Zr₂O₇(HEZO) powders, as an example, could be synthesized with only ~10 wt. % volatilization of NaCl-KCl-NaF salt during 1200 °C treatment, while the resulted powders in traditional “powdery” counterpart contained the segregation phases with a salt loss as high as ~95 wt. %. By simply accommodating the “densified” blocks in a tunnel kiln, a scale-up synthesis of high-entropy ceramics powders by DMMS will be realized toward an industrial production.