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

Molten salt methods have been widely used in the synthesis of high-entropy ceramic powders, yet their scalable production for industrial applications is lacking. In this work, for the first time, a densified microzone molten salt (DMMS) approach was developed for the scale-up preparation of high-entropy ceramic powders, including zirconates, hafnates, silicates, and carbides. The “densified” block of DMMS permitted only trace evaporation of molten salt on surfaces, and the internal “microzone” salt pools significantly promoted the in situ formation of high-entropy phases at relatively low temperatures. Single-phase (La_0.2Nd_0.2Sm_0.2Eu_0.2Gd_0.2)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 resulting powders prepared by the traditional powdery method contained segregation phases with a salt loss as high as ~95 wt%. By simply accommodating the “densified” blocks in a tunnel kiln, scale-up synthesis of high-entropy ceramic powders by DMMS can be realized for industrial production.