Aluminium dodecaboride () is a
superhard
A superhard material is a material with a hardness value exceeding 40 gigapascals (GPa) when measured by the Vickers hardness test. They are virtually incompressible solids with high electron density and high bond covalency. As a result of their u ...
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
with 17%
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
content by weight.
It is the hardest boride of the aluminium-boron system, which also includes , ,
and AlB.
Properties
There are two crystalline forms, α-, and γ-. Both forms are very similar and consist of a framework with three-dimensional networks of and units. The phase β- is now believed to be the ternary boride .
Preparation
The β-form can be prepared by the reaction of
boron(III) oxide
Boron trioxide or diboron trioxide is the boron oxide, oxide of boron with the formula . It is a colorless transparent solid, almost always glassy (amorphous), which can be crystallized only with great difficulty. It is also called boric oxide or b ...
with
sulfur and
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
, then adding
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...
to the mixture.
Uses
The extreme hardness of makes it a favorable component of
PCBN inserts, which are mainly used in cutting and grinding to replace
diamond
Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure, ...
or
corundum.
See also
*
Boron
*
Aluminium boride
Footnotes
External links
"Boron"
{{Borides
Borides
Aluminium compounds