Single crystals of TaB, Ta5B6, Ta3B4 and TAB2, as obtained from high-temperature metal solutions, and their properties

Abstract

Single crystals of TaB, Ta5B6, Ta3B4 and TAB2 of size 0.2-0.4 mm were prepared from high-temperature Al solutions. The crystals were examined by X-ray diffraction and chemical analysis. The Vickers microhardness of the crystals was measured and oxidation at high temperature in air was studied. The TaB, Ta5B6, and Ta3B4 single crystals were obtained as columnar crystals having well-developed {010} and {100} faces. The TaB2 single crystals were obtained as thick platelets with large {0001} planes. The Vickers microhardness of TaB, Ta5B6 and Ta3B4 single crystals measured in several directions on {010} planes ranges from 2330 to 2530 kgf mm-2. The microhardness value on the {0001} planes of TaB2 crystals is in the range of 2780 ~ 2960 kgf mm-2. The oxidation of TaB, Ta5B6, Ta3B4 and TaB2 crystals begins to proceed with a measurable rate in the temperature range 640-680°C. The final oxidation product is Ta2O5.