Tungsten borides

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] 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.

[2] 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.