nitride (BN) exists in a hexagonal modification with a graphite-like crystal structure and a cubic high temperature / high pressure modification with a diamond-like structure.

The most widely used industrial process for the manufacture of hexagonal boron(Ⅲ) nitride is the reaction of boron(Ⅲ) oxide with ammonia at 800 to 1200°C in a calcium phosphate matrix:



After the reaction the matrix is dissolved in cold hydrochloric acid and unreacted boron(Ⅲ) oxide washed out with hot alcohol. A raw product with 80 to 90% purity is thereby obtained. Postreaction in nitrogen at 1800°C or in ammonia at above 1200°C increases the BN-content still further.

A very pure crystalline boron(Ⅲ) nitride is obtained by reacting boron(Ⅲ) oxide with carbon and nitrogen at 1800 to 1900°C:



Hexagonal boron(Ⅲ) nitride is not yet used in large quantities. Interest in this material is increasing, due to its wide application possibilities.

BN-powder is, due to its graphite-like properties, predestined for utilization as a high temperature lubricant or as a mold lubricant in metal casting. Formed articles of boron(Ⅲ) nitride are used as melting crucibles for high purity metals or semiconductor alloys and as refractory linings for plasma burners, rocket jets and combustion chambers. 200 t/a of hexagonal BN were produced in 1995.

Cubic boron(Ⅲ) nitride is manufactured from hexagonal BN in a high pressure synthesis at 50 to 90 kbar and 1500 to 2200°C in the presence of alkali or alkaline earth metals as catalysts. Cubic boron(Ⅲ) nitride is, after diamond, the hardest known material. It is utilized in the grinding agent sector instead of diamond, due to its better chemical resistance at high temperatures.

The market for cubic boron(Ⅲ) nitride was ca. 200 t in 1995.