Tungsten borides

Structure of hexagonal WB2 Structure of orthorhombic β-WB

Tungsten borides are compounds of tungsten and boron. Their most remarkable property is high hardness. The Vickers hardness of WB or WB2 crystals is ~20 GPa[1][2] and that of WB4 is ~30 GPa for loads exceeding 3 N.[3]

## Contents

* 1 Synthesis
* 2 Structure
* 3 Properties
* 4 References

## Synthesis

Single crystals of WB2−x, x = 0.07–0.17 (about 1 cm diameter, 6 cm length) were produced by the floating zone method,[1] and WB4 crystals can be grown by arc-melting a mixture of elemental tungsten and boron.[3]

## Structure

WB2 has the same hexagonal structure as most diborides (AlB2, MgB2, etc.).[4] WB has several forms, α (tetragonal), β (orthorhombic) and δ (tetragonal).[2]

## Properties

δ-WB and WB2 crystals have metallic resistivities of 0.1 and 0.3 mΩ·cm, respectively. The oxidation of W2B, WB and WB2 is significant at temperatures above 600 °C. The final oxidation products contain WO3 and probably amorphous B2O3 or H3BO3. The melting temperatures of W2B, WB and WB2 are 2670, 2655 and 2365 °C, respectively.[2]

Properties  Material  | Vickers hardness (GPa)  | Bulk Modulus (GPa)  | Melting point (°C)

|
|
|

W2B |  |  | 2670
WB | ~20 |  | 2655
WB2 | ~20 |  | 2365
WB4 | ~30 |  |

## References

1. ↑ 1.0 1.1 Otani, S.; Ishizawa, Y. (1995). "Preparation of WB2−x single crystals by the floating zone method". Journal of Crystal Growth 154 (1–2): 81–84. doi:10.1016/0022-0248(95)00155-7. Bibcode: 1995JCrGr.154...81O.
2. ↑ 2.0 2.1 2.2 Okada, S.; Kudou, K.; Lundström, T. (1995). "Preparations and Some Properties of W2B, δ-WB and WB2 Crystals from High-Temperature Metal Solutions". Japanese Journal of Applied Physics 34 (1): 226–231. doi:10.1143/JJAP.34.226. Bibcode: 1995JaJAP..34..226O.
3. ↑ 3.0 3.1 Mohammadi, R.; Lech, A. T.; Xie, M.; Weaver, B. E.; Yeung, M. T.; Tolbert, S. H.; Kaner, R. B. (2011). "Tungsten tetraboride, an inexpensive superhard material". Proceedings of the National Academy of Sciences 108 (27): 10958–62. doi:10.1073/pnas.1102636108. PMID 21690363. Bibcode: 2011PNAS..10810958M.
4. ↑ Woods, H. P.; Wawner, F. E.; Fox, B. G. (1966). "Tungsten Diboride: Preparation and Structure". Science 151 (3706): 75. doi:10.1126/science.151.3706.75. PMID 17842093. Bibcode: 1966Sci...151...75W.

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Tungsten compounds

Tungsten(0)|

* W(CO)6

Tungsten(II)|

* WSi2
* WCl2
* W(OH)2

Tungsten(III)|

* W2O3

Tungsten(IV)|

* WC
* WO2
* WS2
* WSe2
* WTe2
* WF4
* WCl4

Tungsten(V)|

* W2O5
* WBr5
* W2Cl10

Tungsten(VI)|

* H3PW12O40
* (NH4)10(H2W12O42)
* WO2Cl2
* WCl6
* WF6
* WN2
* WO3
* WS3
* WOBr4
* WOCl4
* WOF4
* H2WO4

| Organotungsten(VI) compounds|

* W(CH3)6

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