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

Abstract

The crucible-free reaction between heated tungsten wires and gaseous boron tribromide yields different tungsten borides. The experiments were carried out at various reaction temperatures and times, revealing the formation of W B, WB and WB phases. The underlying reactions were analyzed by using thermodynamic model calculations. The stability of the gaseous tungsten bromides was evaluated using quantum chemical methods. While the developed synthesis of phase-pure borides is only possible to a limited extent, it offers a potential route for a formation of protective coatings with high chemical and thermal resistance.

Preparation of cobalt borides by solid–gas reactions

“…Whether this is the metal boride or free bromine is not selfexplanatory, which became especially clear in former investigations on the tungsten-boron system. 24 The results of the calculations for the region of coexistence between Co and Co 2 B (Fig. 6) suggest the formation of Co 2 B and give an indication as to the composition of the gas phase as a function of temperature.…”

“…In these reactions metal borides and volatile SnCl 2 are formed. 22 Widespread interest in cobalt borides has prompted the application of the hot-wire method, a technique for the preparation of single-phase and chemically pure transition metal borides, 23,24 also to the synthesis of cobalt-boron compounds. In this method metals react with high-purity gaseous boron trihalides ( preferably BBr 3 ) at elevated temperatures.…”

Topotactic BI3-assisted borodization: synthesis and electrocatalysis applications of transition metal borides

“…24 Later, refractory metal borides such as HfB 2 and WB 2 have been prepared by reaction of the resistive heated metal wire with BBr 3 vapor. 11,12 In the current work, we extend BI 3 -assisted synthesis to first row transition metals. Similar to solid state metathesis reactions, the main driving force for this reaction is the formation of thermodynamically stable, watersoluble metal iodides: (nx + 3)M + nBI 3  nM x B + 3MI n (x = 1/6 to 3; n = 2, 3, and 4).…”

“…10 The syntheses of hafnium diboride HfB 2 and tungsten borides WB x were performed by the reaction of a resistive heated metal wire (Hf or W) with boron bromide instead of using a metal halide precursor. 11,12 This method required a sophisticated apparatus to deal with the liquid boron bromide source and the Hf or W metal wire was only partially converted into boride, thus preserving a metallic core.…”

“…10 The syntheses of hafnium diboride HfB 2 and tungsten borides WB x were performed by the reaction of a resistive heated metal wire (Hf or W) with boron bromide instead of using a metal halide precursor. 11,12 This method required a sophisticated apparatus to deal with the liquid boron bromide source and the Hf or W metal wire was only partially converted into boride, thus preserving a metallic core. Fokwa and co-workers developed a straightforward synthesis of nanoscale transition metal borides by reacting anhydrous metal chlorides and elemental boron in Sn ux, which served simultaneously as a hightemperature solvent and as a reducing agent.…”