Synthesis of high-entropy boride powders via boro/carbothermal reduction method

Abstract

In this paper, high-purity and fine (W 0.2 V 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )B 2 (HEB) powders were obtained via a simple high-energy ball milling-assisted boro/carbothermal reduction method at 1600°C. Results showed that the heating temperature and B source contents played a key role in the synthesis of purity of single-phase HEB powders. When excess 10 wt.% B 4 C was introduced, the single-phase HEB powders were synthesized at 1600°C, and its grain size was ~150 nm and it showed the hexagonal crystal structure of metal diborides. EDS results showed the high compositional uniformity of W, V, Ta, Nb, Ti and B elements in HEB powders. Through discussing the thermodynamics process related to these possible chemical reactions and combining the XRD results at different temperatures, it was obtained that higher temperature and enough B source were required to stimulate the formation of high-entropy phase. This work will be a vital step for the commercialization of high-entropy boride powders.

Entropy-Engineered Middle-In Synthesis of Dual Single-Atom Compounds for Nitrate Reduction Reaction

“…35,36 Under an argon-protected environment, as the temperature gradually rises, the preoxidized electrospun fibers commence carbonization, 37 accompanied by a carbothermal reduction process primarily driven by entropy increase. 38 Owing to the slow diffusion rate of solid reactants, heating is required to facilitate the carbothermal reduction. In the bottom-up approach, the solid metal oxides in the middle layer react with carbon, resulting in the formation of metals and gaseous CO. 39 The newly formed metals likely exist in three morphologies: (1) atomically dispersed, akin to SACs 40 ; (2) forming monolayer two-dimensional clusters 41 ; (3) through surface diffusion, monolayer clusters further evolve into threedimensional crystalline particles, 42 which may migrate and coalesce to form larger grains.…”

“…Under an argon-protected environment, as the temperature gradually rises, the preoxidized electrospun fibers commence carbonization, accompanied by a carbothermal reduction process primarily driven by entropy increase . Owing to the slow diffusion rate of solid reactants, heating is required to facilitate the carbothermal reduction.…”

High Entropy Borides Synthesized by the Thermal Reduction of Metal Oxides in a Microwave Plasma

“…This configuration is ideal due its high entropy forming ability of 207 (eV/atom) −1 and theoretical hardness of approximately 33 GPa [15]. also form in this process, which typically necessitates the use of excess boron carbide precursor, the amount of which is experimentally optimized [9]. In contrast, the borothermal reduction (BTR) approach has the benefit of not needing carbon in the precursor mixture, while still forming volatile boron oxides.…”

Synthesis of single‐phase high‐entropy diboride powders and their spheroidization process

“…Recently, several approaches for the synthesis of HEB powders have been reported, including borothermal reduction process, 21,22 boro-carbothermal reduction method, 23,24 molten salt-mediated magnesiothermic reduction method, 25 and so on. showed that the synthesized powders exhibited the mixed phase structure, which suggested that the powder with an incomplete solid solution was prepared.…”

“…Recently, several approaches for the synthesis of HEB powders have been reported, including borothermal reduction process, 21,22 boro‐carbothermal reduction method, 23,24 molten salt‐mediated magnesiothermic reduction method, 25 and so on. Zhang et al 21 .…”