What Is Boron Nitride?
Boron nitride, an inorganic compound made of boron and nitrogen is a colorless and flame-retardant crystal. It has the chemical formula BN, a molecular weight of 24.82, and a CAS No. of 10043-11-5. Its isoelectronic structure with carbon grants it many properties similar to those of carbon.
Structure of Boron Nitride
Boron nitride exists in three main allotropes: hexagonal h-BN (α-BN), cubic c-BN (β-BN), and wurtzite w-BN (γ-BN).
1. Hexagonal (h-BN)
Hexagonal boron nitride, also known as h-BN, α-BN, or graphitic boron nitride, is the most stable form. It features a layered structure akin to graphite, with strong covalent bonds within layers and weak van der Waals forces between them.
2. Cubic (c-BN)
Cubic boron nitride, resembling diamond in structure, is less stable than hexagonal BN. It shares the sphalerite crystal structure with diamond, hence also referred to as β-BN or c-BN.
3. Wurtzite (w-BN)
The wurtzite form, w-BN, mirrors the structure of lonsdaleite, a rare hexagonal carbon polymorph. Its hardness surpasses that of commercial borides but is softer than c-BN.
Properties of Boron Nitride
1. Physical Properties
With high heat resistance, boron nitride can withstand temperatures up to 1,500°C in a vacuum and 2,200°C in an inert atmosphere. Its low thermal expansion coefficient and good thermal conductivity make it an ideal high-thermal-conductivity ceramic.
2. Other Characteristics
Boron nitride also boasts stability against chemicals, excellent corrosion resistance, and insulating properties suitable for high-frequency applications.
Uses of Boron Nitride
Due to its thermal conductivity and electrical insulation, boron nitride is ideal for heat-dissipating resin sheets and substrates, as well as additives in various materials for enhanced heat resistance and lubrication.
Other Information on Boron Nitride
1. Production Process
Boron nitride is produced by heating borax with ammonia or boric acid with ammonium chloride, resulting in a crystalline, scale-like, and slippery material.
2. Legal Information
Not designated under the Poisonous and Deleterious Substances Control Law or the Fire Service Law, boron nitride is listed as a Class 1 Designated Chemical Substance under the PRTR Law.
3. Handling and Storage Precautions
Store in a sealed container in a dry cool place. Use protective gear
when handling and avoid strong oxidizers. In case of contact, wash the affected area with soap and water or rinse eyes with water.