Preparations and Some Properties of W2B, δ-WB and WB2 Crystals from High-Temperature Metal Solutions

Abstract

W2B, δ-WB and WB2 crystals were prepared from high temperature aluminium and copper solutions using tungsten metal and crystalline boron powders as starting material under an argon atmosphere. Growth conditions for obtaining crystals of relatively large size were established. The crystals were examined by X-ray diffraction and chemical analysis. The Vickers microhardness and electrical resistivity of the crystals was measured, and oxidation at high temperature in air was studied. The microhardness value on (001) planes of δ-WB crystals is in the range of 25.3(±0.4)-26.7(±1.2) GPa. The microhardness value on (0001) planes of WB2 crystals is 21.3(±0.4) GPa. The electrical resistivity determined on δ-WB and WB2 crystals are as follows: for δ-WB: 171.5 µ Ω · cm; for WB2: 312.6 µ Ω · cm. The oxidation of W2B, δ-WB and WB2 crystals begins to proceed with a measurable rate in the temperature range 550-730° C. The final oxidation products contain WO3 and probably amorphous B2O3 or H3BO3.