Tungsten Borides

Tungsten borides are compounds of tungsten and boron, and their most remarkable preoperty is high hardness. The Vickers hardness of tungsten borides or tungsten diboride is about 20GPa, and that of WB4 is about 30 GPa for loads exceeding 3 N. 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 temnperatures of W2B, WB and WB2 are 2670, 2655 and 2365 °C, respectively.
WB2 has the same hexagonal structure as most diborides such as AlB2, MgB2 and it has several forms, α (tetragobal), β (orthorombic) and δ (tetragonal).
There are the ways for synthesis the tungsten borides.  Single crystals of WB2−x, x=0.07–0.17 (about 1 cm diameter, 6 cm length) were produced by the floating zone method, and WB4 crystals can be grown by arc-melting a mixture of elemental tungsten and boron.

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