Tantalum borides are compounds of

tantalum Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as ''tantalium'', it is named after Tantalus, a villain in Greek mythology. Tantalum is a very hard, ductile, lustrous, blue-gray transition metal that is ...

and

boron Boron is a chemical element with the 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 th ...

most remarkable for their extreme

hardness In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...

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 t ...

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 lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a r ...

Thallium(I) iodide Thallium(I) iodide is a chemical compound with the formula TlI. It is unusual in being one of the few water-insoluble metal iodides, along with AgI, CuI, SnI2, SnI4, PbI2 and HgI2. Chemistry TlI can be formed in aqueous solution by metathes ...

-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'' has ...

aluminum diboride Aluminium diboride (AlB2) is a chemical compound made from the metal aluminium and the metalloid boron. It is one of two compounds of aluminium and boron, the other being AlB12, which are both commonly referred to as aluminium boride. Structura ...

-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