Facile Electrochemical Preparation of Nano-sized Ultra-high-temperature Ta_1−xHf_xC Ceramic Powders

Abstract

Nano-sized powders of the Ta1-xHfxC class of ceramics, with compositions of Ta0.2Hf0.8C, Ta0.5Hf0.5C and Ta0.8f0.2C, were successfully synthesized from mixtures of the corresponding metal oxides and graphite by electro-deoxidation in molten CaCl2 at 1173 K. X-ray diffraction revealed that the as-prepared Ta0.8Hf0.2C mixed carbide had a single-phase cubic structure whereas Ta0.5Hf0.5C and Ta0.2Hf0.8C had dual-phase cubic structures, indicating that the large proportion of Ta promoted the formation of a homogeneous solid solution of TaC and HfC during synthesis. Electron microscopy proved that the particle size of the mixed carbides was in the nano range, while energy-dispersive spectroscopy and X-ray photoelectron spectroscopy confirmed that the intended compositions had been attained. Notably, the electrochemical method of synthesizing Ta1-xHfxC mixed carbides proceeds at a significantly lower temperature than the conventional preparation methods. This offers a number of key advantages in that it saves energy, gives better control over composition and allows for higher purity, and suppresses in situ sintering to enable the formation of nanoparticles.

Electrolysis Synthesis of Carbides and Carbon Dioxide Capture in Molten Salts

“…c) XRD patterns of Ta 0.8 Hf 0.2 C, Ta 0.5 Hf 0.5 C, and Ta 0.2 Hf 0.8 C powders prepared in molten CaCl 2 of 900 °C at 3.1 V for 8 h. Reproduced with permission. [ 27 ] Copyright 2022, Electrochemical Society, Inc. d) XRD patterns of the Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 C powders synthesized from TiO 2 , ZrO 2 , HfO 2 , Nb 2 O 5 , Ta 2 O 5 , C mixture (C1: (TiO 2 ) 0.2 (NbO 2.5 ) 0.2 (TaO 2.5 ) 0.2 (ZrO 2 ) 0.2 (HfO 2 ) 0.2 C 1.0 , C2: (TiO 2 ) 0.2 (NbO 2.5 ) 0.2 (TaO 2.5 ) 0.2 (ZrO 2 ) 0.2 (HfO 2 ) 0.2 C 1.5 ) in molten CaCl 2 of 900 °C at 3.1 V. Reproduced with permission. [ 28 ] Copyright 2020, Wiley‐VCH.…”

“…The anode is usually graphite, or some inert materials that do not participate in the anodic reaction. The progress of electrochemical technology depends on a deeper understanding of [20][21][22][23][24][25][26][27][28][29] d) Illustration of electrolysis synthesis of carbides coupled with CO 2 capture. complex reactions on electrodes, which is related to the exquisite control of electrolysis parameters, electrolyte composition, and electrode architectures.…”

“…The similar process can be applied to the synthesis of V-Al-C and Cr-Al-C MAX phases. [27,[66][67][68][69] After electrolysis, some impurities in raw materials such as magnesium oxide, calcium oxide, aluminum oxide, iron oxide, and manganese oxide will not affect the final product. For Si, it can be dissolved into the product without forming unexpected phases in the electrolysis product.…”

“…c) XRD patterns of Ta 0.8 Hf 0.2 C, Ta 0.5 Hf 0.5 C, and Ta 0.2 Hf 0.8 C powders prepared in molten CaCl 2 of 900 °C at 3.1 V for 8 h. Reproduced with permission. [27] Copyright 2022, Electrochemical Society, Inc. ) in molten CaCl 2 of 900 °C at 3.1 V. Reproduced with permission. [28] Copyright 2020, Wiley-VCH.…”

“…c) Development process of electrolysis synthesis of carbides in molten salts. [ 20–29 ] d) Illustration of electrolysis synthesis of carbides coupled with CO 2 capture.…”