Mechanochemical synthesis and annealing of tungsten di‐ and tetra‐boride

Abstract

Tungsten diboride and tetra‐boride were synthesized by a combination of mechanochemical method and the subsequent heat treatment. To clarify the formation process of tungsten diboride (WB2) and tetra‐boride (WB4) using W‐B mixture system with variable B concentration, the effects of ball‐to‐powder ratio, W to B molar ratio on mechanochemical process were studied, and the relationship between phase composition and annealing temperature was built. The results show that, the synthesis of WB2 with W:B = 1:5 can be improved by increasing ball‐to‐powder ratio from 4:1 to 6:1, but no WB4 phase can be directly synthesized by mechanochemical method. WB2 (AlB2‐WB2, P6/mmm) phase can be only synthesized with W to B molar ratio of 1:4 and 1:5. Further increase in B content to W:B = 1:6 or less, W was present as the main phase with high crystallinity (>71%). WB4 phase was formed as an annealing temperature as low as 1000°C, which was not stable and may decompose to WB2 (WB2‐WB2, P6/mmm) phase with the increase in temperature. The decomposition temperature of WB4 can be improved by increasing the B content. Compared with the W‐B mixtures (W:B = 1:12) being milled for 1 hour, the powders milled for 40 hours present 20% higher of WB4 weight fraction after being annealed at 1400°C for 2 hours.

Understanding the Hardness of Doped WB4.2

“…[1][2][3][4] A number of transition metal borides have Vicker's hardness greater than 40 GPa and bulk modulus larger than 300 GPa, which, coupled with their metallic nature and inexpensiveness, makes them excellent materials for superhard coating and cutting tools. [5][6][7][8] A vast number of superhard metal borides with various crystal structures has been discovered in recent years, including mono- 8,9 , di- 5,6,10 , tetra- [11][12][13][14] , and dodecaborides 15,16 , as well as their solid solutions. It has been experimentally shown that the hardness of materials of this class can be controlled through intrinsic-originating from local chemical bonding-and extrinsic-resulting from surface grain boundaries and pattering-hardening effects.…”

“…A vast number of superhard metal borides with various crystal structures have been discovered in recent years, including mono-, , di-, ,, tetra-, − and dodecaborides, , as well as their solid solutions. It has been experimentally shown that the hardness of materials of this class can be controlled through intrinsic originating from local chemical bondingand extrinsic resulting from surface grain boundaries and patterninghardening effects.…”

Design of metal‐substituted tungsten diboride as an efficient bifunctional electrocatalyst for hydrogen and oxygen evolution

“…The catalysts synthesized by molten salt differ from carbothermal reduction ones in terms of peak intensity and broadening, implying that the XRD peaks of W (1‐ x ) TM x B 2 /ms catalysts are broader in contrast to those of W (1‐ x ) TM x B 2 /ct. As a result, W (1‐ x ) TM x B 2 /ms samples are more nano‐sized compared to the W (1‐ x ) TM x B 2 /ct ones 33 . Scherrer’s equation is applied to calculate the average particle size (D) of the nanoparticles for each sample (peak 101). where k = 0.94 is the shape factor of a particle, presuming the shape of the nanoparticles as a sphere, λ = 1.5406 Å is the wavelength of Cu Kα radiation, β is the FWHM of the XRD (101) peak, and θ is the diffraction angle of the peak 29 .…”

“…As a result, W (1-x) TM x B 2 /ms samples are more nano-sized compared to the W (1-x) TM x B 2 /ct ones. 33 Scherrer's equation is applied to calculate the average particle size (D) of the nanoparticles for each sample (peak 101).…”

Understanding Hardness of Doped WB4.2

“…[1][2][3][4] A number of transition metal borides have Vicker's hardness greater than 40 GPa and bulk modulus larger than 300 GPa, which, coupled with their metallic nature and inexpensiveness, makes them excellent materials for superhard coating and cutting tools. [5][6][7][8] A vast number of superhard metal borides with various crystal structures has been discovered in recent years, including mono- 8,9 , di- 5,6,10 , tetra- [11][12][13][14] , and dodecaborides 15,16 , as well as their solid solutions. It has been experimentally shown that the hardness of materials of this class can be controlled through intrinsic-originating from local chemical bonding-and extrinsic-resulting from surface grain boundaries and pattering-hardening effects.…”