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Tungsten borides
Chemical compound

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 and that of WB4 is ~30 GPa for loads exceeding 3 N.

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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,4 and WB4 crystals can be grown by arc-melting a mixture of elemental tungsten and boron.5

Structure

WB2 has the same hexagonal structure as most diborides (AlB2, MgB2, etc.).6 WB has several forms, α (tetragonal), β (orthorhombic) and δ (tetragonal).7

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.8

Properties
MaterialVickers hardness (GPa)Bulk Modulus (GPa)Melting point (°C)
W2B2670
WB~202655
WB2~202365
WB4~30

References

  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. Bibcode:1995JCrGr.154...81O. doi:10.1016/0022-0248(95)00155-7. /wiki/Bibcode_(identifier) ↩

  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. Bibcode:1995JaJAP..34..226O. doi:10.1143/JJAP.34.226. S2CID 95651766. /wiki/Bibcode_(identifier) ↩

  3. 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. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3131357 ↩

  4. 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. /wiki/Bibcode_(identifier) ↩

  5. 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. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3131357 ↩

  6. 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. /wiki/Bibcode_(identifier) ↩

  7. 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. /wiki/Bibcode_(identifier) ↩

  8. 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. /wiki/Bibcode_(identifier) ↩