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]

## Synthesis

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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

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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

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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

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1. ^ a b 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\. Bibcode:1995JCrGr.154...81O. doi:10.1016/0022-0248(95)00155-7.1–2&rft.pages=81-84&rft.date=1995&rft_id=info:doi/10.1016/0022-0248(95)00155-7&rft_id=info:bibcode/1995JCrGr.154...81O&rft.aulast=Otani&rft.aufirst=S.&rft.au=Ishizawa,+Y.&rfr_id=info:sid/en.wikipedia.org:Tungsten+borides" class="Z3988">
2. ^ a b c 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\. Bibcode:1995JaJAP..34..226O. doi:10.1143/JJAP.34.226. S2CID 95651766.
3. ^ a b 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\. Bibcode:2011PNAS..10810958M. doi:10.1073/pnas.1102636108. PMC 3131357. PMID 21690363.
4. ^ Woods, H. P.; Wawner, F. E.; Fox, B. G. (1966). "Tungsten Diboride: Preparation and Structure". Science. 151 (3706): 75. Bibcode:1966Sci...151...75W. doi:10.1126/science.151.3706.75. PMID 17842093. S2CID 7686903.

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Tungsten compounds

Tungsten(0)|

* W(CO)6
* W(PMe3)6

Tungsten(II)|

* WSi2
* WCl2
* WI2
* W(OH)2
* W2(hpp)4

Tungsten(III)|

* W2O3
* WCl3
* WI3
* W2(OtBu)6

Tungsten(IV)|

* WC
* WO2
* WS2
* WSe2
* WTe2
* WF4
* WCl4
* WBr4
* WI4

Tungsten(V)|

* WBr5
* W2Cl10
* LiWF6

Tungsten(V,VI)|

* "W2O5"

Tungsten(VI)|

* WO2Cl2
* WBr6
* WCl6
* WF6
* WN2
* WO3
* WS3
* WAs2
* WOBr4
* WOCl4
* WOF4
* H2WO4

| Organotungsten(VI) compounds|

* W(CH3)6

|

Polytungstate salts|

* H3PW12O40
* (NH4)10(H2W12O42)
* Na6[H2W12O40]

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Borides Bxy-

| BxHy |  |  |  | He

|
|
|
|

Li  | Be  | B | C  | N  | O  | F  | Ne
Na  | MgB2 | AlB2
AlB12 | SiBx | P  | S  | Cl  | Ar
K  | CaB4
CaB6 |  | ScB12 | TiB2 | V  | CrB | Mn  | FeB4
FexBy | CoxBy | Ni3B
Ni2B | Cu  | Zn  | Ga  | Ge  | As  | Se  | Br  | Kr
Rb  | SrB6 |  | YBx | ZrB2 | NbB2 | Mo  | Tc  | RuBx | Rh  | Pd  | Ag  | Cd  | In  | Sn  | Sb  | Te  | I  | Xe
Cs  | BaB6 | *  | LuB4
LuB6 | HfB2 | TaBx | WxBy | ReB2 | OsBx | Ir  | Pt  | Au  | Hg  | Tl  | Pb  | Bi  | Po  | At  | Rn
Fr  | Ra  | **  | Lr  | Rf  | Db  | Sg  | Bh  | Hs  | Mt  | Ds  | Rg  | Cn  | Nh  | Fl  | Mc  | Lv  | Ts  | Og

*  | LaB4
LaB6 | CeB4
CeB6 | PrB4
PrB6 | NdB4
NdB6 | Pm  | SmB4
SmB6 | EuB6 | GdB4
GdB6 | TbB4
TbB6 | DyB4
DyB6 | HoB4
HoB6 | ErB4
ErB6 | TmB4
TmB6 | YbB4
YbB6
**  | Ac  | Th  | Pa  | UB2 | Np  | PuBx | Am  | Cm  | Bk  | Cf  | Es  | Fm  | Md  | No
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