Crucible‐Free Preparation of Transition‐Metal Borides: HfB₂

Abstract

This study gives an account of an innovative, crucible-free technique for the synthesis of single-phase borides at relatively moderate temperatures. A metal wire heated by an electrical current reacts with a chosen gaseous boron halide in a gas/solid reaction yielding a single-phase, oxygen- and carbon-free product, as evidenced by X-ray powder diffraction and chemical analysis. This method is demonstrated using the example of hafnium reacting with boron tribromide. Preliminary thermodynamic considerations show that this kind of crucible-free synthesis specifically enables the preparation of borides of transition metals and similar elements.

A Hydride Route to Ternary Alkali Metal Borides: A Case Study of Lithium Nickel Borides

“…[7][8][9] Recently,r eactiveb oron halide precursors have been exploredf or the rapid synthesis of binary borides, including refractoryH fB 2 (m.p. 3473 K) [19] and Mo 2 B 4 -based hydrogenevolution reactionc atalysts. [20] Single-crystal growth from reactive Li or Mg fluxes was employed, including growth under high-pressurec onditions.…”

Tungsten Borides: On the Reaction of Tungsten with Boron(III) Bromide

“…As mentioned in the beginning, the Hf−BBr 3 system is considerably different from the W−BBr 3 one. Hafnium diboride is formed exclusively in a form of a porous layer.…”

“…The formation of hafnium diboride by reaction of metallic hafnium with boron tribromide via hot‐wire method has been recently reported . Phase‐pure HfB 2 in form of a porous layer was obtained by reacting gaseous BBr 3 with a hafnium wire heated by electrical current to temperatures between 800 and 1200 °C.…”

Revealing the Unusual Rigid Boron Chain Substructure in Hard and Superconductive Tantalum Monoboride

“…The high valence electron density (VED) of transition metals gives their compoundsh igh bulk modulus, ands trong covalentb onds between light elements (LEs) induceh igh shear modulus.B oth merits of high bulk modulus (B)a nd shear modulus (G), benefitted from their constituent components, guarantee transition metal light element compounds (TMLEs) potential high hardness. [10][11][12][13][14][15][16] The TMÀTM bonds in the TMLEsp rovide electron-transporting paths in the crystal structures. So,t he TMLEsu sually possess both high hardness and electricalc onductivity at the same time.…”

“…Previous studies particularly focusedo nd esigning and synthesizingb orides with high boron concentration. Many boridesw ith extremely high boron content, such as tetraborides (WB 4 ,C rB 4 ,F eB 4 ,M nB 4 )a nd even dodecaborides (ZrB 12 ,S cB 12 ,Y B 12 ), have been synthesized. [23][24][25][26][27][28] However,i ti s still challenging to incorporate more boron atoms into most transition metal latticesw ith aB:TM molar ratio exceeding 4:1, due to their harsh synthesis conditions.…”