Synthesis of High-entropy Carbide Nano Powders via Liquid Polymer Precursor Route

Abstract

High entropy carbide ceramics have been proposed in recent years for their promising properties as high hardness, high modulus and low thermal conductivity. Liquid polymer precursor method, of which multiple elements distribute homogeneously during the pyrolysis process, is considered to be favorable in fabricating high entropy ceramics. However, few reports have studied the synthesis of liquid precursor. In this work, liquid polymer precursor of (Ti, Zr, Hf, Ta)C were synthesized by co-hydrolysis and polycondensation of equiatomic metal containing monomers, and adding allyl-functional novolac resin (AN) as carbon source. The obtained polymer precursors of high entropy carbide ceramics (PHECs) were soluble in propyl alcohol and stable for months. The corresponding high entropy carbide ceramic nano powders were obtained by pyrolyzing PHEC at 1800℃ for 2 h in vacuum. The precursors and ceramic powders were characterized by different methods. Results reveal that the ceramic sample pyrolyzed at 800℃ are composed of t-ZrO2 and oxide solid solutions, and carbothermal reduction reaction began after pyrolyzed at 1000℃, with carbide solid solutions being generated. After being pyrolyzed at 1800℃, the samples convert to target high entropy carbide ceramics. As-obtained ceramics are characterized to be high purity with uniform distribution of nanosized particles (~100 nm). The synthesized precursor has high ceramic yield (28.6wt%), low viscosity (150 mPa•s), and good solubility in polar solvents. Therefore, the proposed liquid polymer precursor method is reliable in preparation of high entropy ceramic nano powders, ceramic fibers and ceramic matrix composites.