Tantalum boride


Tantalum borides are compounds of tantalum and boron most remarkable for their extreme hardness.

Properties

The Vickers hardness of TaB and TaB2 films and crystals is ~30 GPa. Those materials are stable to oxidation below 700 °C and to acid corrosion.
TaB2 has the same hexagonal structure as most diborides. The mentioned borides have the following space groups: TaB, Ta5B6, Ta3B4, TaB2.

Preparation

Single crystals of TaB, Ta5B6, Ta3B4 or TaB2 can be produced by the floating zone method.
Tantalum boride films can be deposited from a gas mixture of TaCl5-BCl3-H2-Ar in the temperature range 540–800 °C. TaB2 is deposited at a source gas flow ratio of six and a temperature above 600 °C. TaB is deposited at BCl3/TaCl5 = 2–4 and T = 600–700 °C.
Nanocrystals of TaB2 were successfully synthesized by the reduction of Ta2O5 with NaBH4 using a molar ratio M:B of 1:4 at 700-900 °C for 30 min under argon flow.