Abstract:Superhard metals are of interest as possible replacements with enhanced properties over the metal carbides commonly used in cutting, drilling, and wear-resistant tooling. Of the superhard metals, the highest boride of tungsten-often referred to as WB 4 and sometimes as W 1-x B 3 -is one of the most promising candidates. The structure of this boride, however, has never been fully resolved, despite the fact that it was discovered in 1961-a fact that severely limits our understanding of its structure-property rel… Show more
“…8 B 3(hex) with one-third of the metal atoms absent, however, it also contains partially filled tungsten sites as well as boron atom trimers (Figure 12). [188,189,298] …”
Section: Of 29) 1604506mentioning
confidence: 99%
“…Most notably, WB 4 requires a tungsten to boron ratio of 1:12 in order to form, as only this ratio prevents the formation of the thermodynamically favorable WB 2 phase. [188,189,279,280,383] For the synthesis of polycrystalline samples, the most common technique used is arc-melting of pressed metal and boron powders of appropriate stoichiometry on top of a copper water-cooled hearth in an inert atmosphere of argon or helium. The successful synthesis of metal borides using powders of pure metals and amorphous or crystalline boron via arc-melting includes such classes of borides as: 1) Lower metal borides and their alloys, e.g., TiB; [122] W 1−x Ta x B; [293] [51,268] and ZrB 12 ; [268,332] 4) β-rhombohedral boron [311] and its transition metal doping phases (HfB 50 , ScB 50 ); [50,55] and 5) YPtB 50 ; [388] Another common boride synthesis technique is hot-pressing of mixtures of transition metal and boron powders; using this method boride tools can also be readily made.…”
Section: ) Carbothermal Reduction (Reduction Of Metal Oxides and Bormentioning
For decades, borides have been primarily studied as crystallographic oddities. With such a wide variety of structures (a quick survey of the Inorganic Crystal Structure Database counts 1253 entries for binary boron compounds!), it is surprising that the applications of borides have been quite limited despite a great deal of fundamental research. If anything, the rich crystal chemistry found in borides could well provide the right tool for almost any application. The interplay between metals and the boron results in even more varied material's properties, many of which can be tuned via chemistry. Thus, the aim of this review is to reintroduce to the scientific community the developments in boride crystal chemistry over the past 60 years. We tie structures to material properties, and furthermore, elaborate on convenient synthetic routes toward preparing borides.
“…8 B 3(hex) with one-third of the metal atoms absent, however, it also contains partially filled tungsten sites as well as boron atom trimers (Figure 12). [188,189,298] …”
Section: Of 29) 1604506mentioning
confidence: 99%
“…Most notably, WB 4 requires a tungsten to boron ratio of 1:12 in order to form, as only this ratio prevents the formation of the thermodynamically favorable WB 2 phase. [188,189,279,280,383] For the synthesis of polycrystalline samples, the most common technique used is arc-melting of pressed metal and boron powders of appropriate stoichiometry on top of a copper water-cooled hearth in an inert atmosphere of argon or helium. The successful synthesis of metal borides using powders of pure metals and amorphous or crystalline boron via arc-melting includes such classes of borides as: 1) Lower metal borides and their alloys, e.g., TiB; [122] W 1−x Ta x B; [293] [51,268] and ZrB 12 ; [268,332] 4) β-rhombohedral boron [311] and its transition metal doping phases (HfB 50 , ScB 50 ); [50,55] and 5) YPtB 50 ; [388] Another common boride synthesis technique is hot-pressing of mixtures of transition metal and boron powders; using this method boride tools can also be readily made.…”
Section: ) Carbothermal Reduction (Reduction Of Metal Oxides and Bormentioning
For decades, borides have been primarily studied as crystallographic oddities. With such a wide variety of structures (a quick survey of the Inorganic Crystal Structure Database counts 1253 entries for binary boron compounds!), it is surprising that the applications of borides have been quite limited despite a great deal of fundamental research. If anything, the rich crystal chemistry found in borides could well provide the right tool for almost any application. The interplay between metals and the boron results in even more varied material's properties, many of which can be tuned via chemistry. Thus, the aim of this review is to reintroduce to the scientific community the developments in boride crystal chemistry over the past 60 years. We tie structures to material properties, and furthermore, elaborate on convenient synthetic routes toward preparing borides.
“…For example, at least five different binary compounds formed between tungsten and boron have been reported: W 2 B, WB (two crystal structures), WB 2 , W 2 B 4 (formerly described as W 2 B 5 ), and WB 4 [1][2][3][4]. Metal borides also exhibit a range of interesting physical properties, including superconductivity [5] and superhardness [6].…”
Understanding different bonding environments in various metal borides provides insight into their structures and physical properties. Polycrystalline aluminum diboride (AlB 2 ) samples have been synthesized and compared both with a commercial sample and with the literature. One issue that arose is the relative ease with which boron-rich and aluminum deficient phases of aluminum borides can be presented in AlB 2 . Here, we report 27 Al, 11 B nuclear magnetic resonance (NMR) spectroscopy and first-principles calculations on AlB 2 in order to shed light on these different bonding environments at the atomic level and compare the structural and electronic properties of the products of different preparations. Along with the aforementioned, the present study also takes an indepth look at the nature of the 11 B and 27 Al nuclear spin-lattice relaxation recovery data for the AlB 2 and other superhard materials. The nuclear spinlattice relaxation has been measured for a static sample and with magic-angle spinning. The combination of NMR and band structure calculations highlights the synthetic challenges with superhard materials.
“…The highest boron content is chosen following ref. 9.Figure 2Enthalpies of formation for structures derived from hP 16-WB 3 by selective removal of tungsten atoms and/or contamination by additional boron atoms. ( a ) and ( b ) Show the same results organized in two different ways described in the text.…”
Two-dimensional systems have strengthened their position as a key materials for novel applications. Very recently, boron joined the distinguished group of elements confirmed to possess 2D allotropes, named borophenes. In this work, we explore the stability and hardness of the highest borides of tungsten, which are built of borophenes separated by metal atoms. We show that the WB3+x compounds have Vickers hardnesses approaching 40 GPa only for small values of x. The insertion of extra boron atoms is, in general, detrimental to the hardness of WB3 because it leads to the formation of quasi-planar boron sheets that are less tightly connected with the adjacent tungsten layers. Very high concentrations of boron (x ≈ 1), give rise to a soft (Vickers hardness of ~8 GPa) and unstable hP20-WB4 structure that can be considered to be built of quasi-planar boron α-sheets separated by graphitic tungsten layers. By contrast, we show that the formation of tungsten vacancies leads to structures, e.g. W0.75B3+x, with Vickers hardnesses that are not only similar in value to the experimentally reported load-independent hardnesses greater than 20 GPa, but are also less sensitive to variations in the boron content.
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