Tantalum borides are compounds of

tantalum Tantalum is a chemical element; it has Symbol (chemistry), symbol Ta and atomic number 73. It is named after Tantalus, a figure in Greek mythology. Tantalum is a very hard, ductility, ductile, lustre (mineralogy), lustrous, blue-gray transition ...

and

boron Boron is a chemical element; it has symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the boron group it has three ...

most remarkable for their extreme

hardness In materials science, hardness (antonym: softness) is a measure of the resistance to plastic deformation, such as an indentation (over an area) or a scratch (linear), induced mechanically either by Pressing (metalworking), pressing or abrasion ...

Properties

The

Vickers hardness The Vickers hardness test was developed in 1921 by Robert L. Smith and George E. Sandland at Vickers Ltd as an alternative to the Brinell method to measure the hardness of materials. The Vickers test is often easier to use than other 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 (AlB₂, MgB₂, etc.). The mentioned borides have the following space groups: TaB (

orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic Lattice (group), lattices result from stretching a cubic crystal system, cubic lattice along two of its orthogonal pairs by two different factors, res ...

Thallium(I) iodide Thallium(I) iodide is a chemical compound with the formula . It is exists as both a solid and high temperature red polymorph. Thallium(I) iodide is one of several water-insoluble metal iodides, along with AgI, CuI, SnI2, SnI4, PbI2, and Hg ...

-type, Cmcm), Ta₅B₆ (Cmmm), Ta₃B₄ (Immm), TaB₂ (

hexagonal In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°. Regular hexagon A regular hexagon is d ...

, aluminum diboride-type, P6/mmm).

Preparation

Single crystals of TaB, Ta₅B₆, Ta₃B₄ or TaB₂ (about 1 cm diameter, 6 cm length) 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 (single-phase) is deposited at a source gas flow ratio (BCl₃/TaCl₅) of six and a temperature above 600 °C. TaB (single-phase) 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. :Ta₂O₅ + 6.5 NaBH₄ → 2 TaB₂ + 4 Na(g,l) + 2.5 NaBO₂+ 13 H₂(g)

References

{{Borides Tantalum compounds Borides Superhard materials