Preparation of (Zr0.25Hf0.25Ta0.25Nb0.25)C high-entropy ceramic nanopowders via liquid-phase precursor route at a low temperature of 1500 °C

Abstract

Using citric acid, ethylene glycol, ZrOCl2·8H2O, HfOCl2·8H2O, NbCl5, and TaCl5 as raw materials, based on the principle of Pechini coordination polymerization, the (Zr0.25Hf0.25Ta0.25Nb0.25)C high-entropy ceramic precursor solution was successfully prepared, and the corresponding high-entropy ceramic powder was formed by pyrolysis at a low temperature of 1500 °C. The molecular structure of the precursor and its pyrolysis products were analyzed and characterized by different analytical and testing methods. The results show that in the precursor solution, the organic compound and the metal ions form a stable three-dimensional macromolecular structure, so that the metal ions show a uniform distribution at the molecular level, shortening the diffusion path during the carbothermal reduction reaction, thereby enabling the formation of the single-phase high-entropy carbide ceramic powders at a relatively low temperature. The obtained ceramic powders have high purity, uniform element distribution, with an average particle diameter of approximately 42 nm and an oxygen content of about 1.61 wt%. The precursor solution prepared in this study has a moderate viscosity of 20–50 mPa s and a high ceramic yield of 45 %, which is ideal for the preparation of high-entropy ceramic matrix composites.