Tungsten borides

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]

Contents

Synthesis

Single crystals of WB2-x, x=0.07–0.17 (about 1 cm diameter, 6 cm length) can be produced by the floating zone method.[1]

Structure

WB2 has the same hexagonal structure as most diborides (AlB2, MgB2, etc.).[3] WB has several forms, α(tetragonal), β (orthorombic) and δ (tetragonal).[2]

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 temnperatures of W2B, WB and WB2 are 2670, 2665 and 2365 °C, respectively.[2]

References

  1. ^ a b S. Otani and Y. Ishizawa "Preparation of WB2-x single crystals by the floating zone method" J. Cryst. Growth 154 (1995) 81
  2. ^ a b c S. Okada et al. "Preparations and Some Properties of W2B, δ-WB and WB2 Crystals from High-Temperature Metal Solutions" Jpn. J. Appl. Phys. 34 (1995) 226
  3. ^ H. P. Woods et al. "Tungsten Diboride: Preparation and Structure" Science 151 (1966) 3706