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]
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]
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]
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]
Material | Vickers hardness (GPa) | Bulk Modulus (GPa) | Melting point (°C) |
---|---|---|---|
W2B | 2670 | ||
WB | ~20 | 2655 | |
WB2 | ~20 | 2365 | |
WB4 | ~30 |
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]
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]
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]
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]
Material | Vickers hardness (GPa) | Bulk Modulus (GPa) | Melting point (°C) |
---|---|---|---|
W2B | 2670 | ||
WB | ~20 | 2655 | |
WB2 | ~20 | 2365 | |
WB4 | ~30 |