Aluminium dodecaboride

Aluminium dodecaboride (AlB12) is a superhard chemical compound with 17% aluminium content by weight.

It is the hardest boride of the aluminium-boron system, which also includes AlB10, AlB4, AlB2 and AlB.

Properties
There are two crystalline forms, α-AlB12, and γ-AlB12. Both forms are very similar and consist of a framework with three-dimensional networks of B12 and B20 units. The phase β-AlB12 is now believed to be the ternary boride C2Al3B48.

Preparation
The β-form can be prepared by the reaction of boron(III) oxide with sulfur and aluminium, then adding carbon to the mixture.

Uses
The extreme hardness of AlB12 makes it a favorable component of PCBN inserts, which are mainly used in cutting and grinding to replace diamond or corundum.