Facile Electrochemical Synthesis of Nanoscale (TiNbTaZrHf)C High‐Entropy Carbide Powder

Abstract

High-entropy alloys and compounds are becoming an important class of new materials due to their outstanding refractory and high-temperature properties. However, preparation in bulk quantities and in powder form via classical metallurgical methods is challenging. Here, we report the first synthesis of an ultra-high-temperature high-entropy carbide, (TiNbTaZrHf)C, via a facile electrochemical process. In this, a mixture of the individual metal oxides and graphite is deoxidised in a melt of CaCl 2 at a temperature of only 1173 K. The (TiNbTaZrHf)C prepared is single-phase fcc and has a powdery morphology with a particle-size range of 15-80 nm. Such materials are in demand for modern additive manufacturing techniques, while preliminary tests have also indicated a possible application in supercapacitors. The successful synthesis of (TiNbTaZrHf)C powder may now guide the way towards establishing the electrochemical route for the preparation of many other entropy-stabilised materials. Entropy-stabilised materials are presently gaining considerable attention. Yeh et al. [1] and Cantor et al. [2] incepted the fundamental concept of entropy stabilisation in 2004 by preparing equiatomic multi-component alloys with a singlephase crystal structure. It was soon realised that the combination of complex chemistry and simple crystallography, together with the large compositional design space, would provide fundamentally new alloys with exceptional mechanical and thermal as well as oxidation-and corrosion-resistant properties. [3-5] In the last five years, the concept of entropy stabilisation has been extended further towards high-entropy oxides, borides, nitrides, and carbides. [6-13] The borides, nitrides, and carbides of Group-IV and-V transition metals, known as ultra-high-temperature ceramics (UHTCs), have long been of interest because their properties often exceed those of the corresponding metals. [14, 15] Bulk quantities of UHTCs are conventionally prepared by hightemperature reactions, posing problems in achieving high purity, homogeneous chemical and phase compositions, and controlled particle size, especially at the nanoscale. Likewise, high-entropy carbides (HECs) are prepared by mechanical milling and subsequent spark-plasma sintering or by carbothermal reduction, both at temperatures around 2273 K, yielding either almost dense bodies or coarse micron-sized powders. [9-13] Consequently, major research efforts are underway worldwide with the aim of making high-entropy materials in bulk quantities and in nanopowder form. The present study introduces a novel, facile, and singlestep method for the synthesis of HECs by harnessing the FFC-Cambridge electro-deoxidation process. [16] This process was originally developed for the preparation of metals directly from their oxides. It relies on making the metal oxide the cathode in a melt of CaCl 2 electrolyte and polarising it vs. a carbon anode such that the oxide ions from the cathode are expelled into the electrolyte. The versatility of the FFC process has been highlighted in...

High‐Entropy‐Alloy Nanoparticles with Enhanced Interband Transitions for Efficient Photothermal Conversion

“…For the HEANPs which composited more than five elements, their Δ S mix is all above 1.5R, which is in agreement with the high entropy classification (Figure S20, Table S1, Supporting Information) [18] . To confirm the phase structure of different HEANPs, X‐ray diffraction (XRD) has been employed (Figure S18, Supporting Information), and the FCC crystal structure of all HEANPs evidences that the different elements are uniformly mixed into a solid solution after the ultrafast‐cooling treatment [33, 34] . It is found that the as‐made nanoparticle is easily oxidized once it has been synthesized, [16] and the surface element distributions tested by X‐ray photoelectron spectroscopy (XPS) prove the uniform dielectric metal oxide shells outside the nanoparticle (Figures S21 to S32, Supporting Information) [35, 36] …”

High‐Entropy‐Alloy Nanoparticles with Enhanced Interband Transitions for Efficient Photothermal Conversion

“…[18] To confirm the phase structure of different HEANPs,X -ray diffraction (XRD) has been employed (Figure S18, Supporting Information), and the FCC crystal structure of all HEANPs evidences that the different elements are uniformly mixed into as olid solution after the ultrafast-cooling treatment. [33,34] It is found that the as-made nanoparticle is easily oxidized once it has been synthesized, [16] and the surface element distributions tested by X-ray photoelectron spectroscopy (XPS) prove the uniform dielectric metal oxide shells outside the nanoparticle (Figures S21 to S32, Supporting Information). [35,36] Theoptical absorption properties of HEANPs have been investigated by the scattering spectra over aw avelength region of UV/Vis-NIR (250 to 2500 nm) (Figure S33, Supporting Information), showing the significantly improved solar absorption performance with the increasing element number.…”

Electrical Discharge Induced Bulk‐to‐Nanoparticle Transformation: Nano High‐Entropy Carbide as Catalysts for Hydrogen Evolution Reaction

“…[14][15][16][17][18][19] Unfortunately, catalysts based on high-entropy carbide (HEC) are still in their infancy because the synthesis of HEC nanomaterials is a great challenge. Although carbothermic reduction, [20] polymer precursor, [21] and molten-salt elector-deoxidation [22] have been utilized to synthesize HEC, the resultant materials are generally of sub-micron or even micron levels, which are too large for electrocatalytic application. Recently, high entropy Mo 0.2 W 0.2 V 0.2 Cr 0.2 Nb 0.2 C nanoparticles were prepared by a complicated coordination-assisted crystallization process in the presence of Br-based poly (ionic liquids).…”