Cubic Boron Nitride (BN) Nanopowder
Purity: 99.9% Size: 200 nm
Cubic boron nitride has a crystal structure similar to that of diamond. Just as diamond is less stable than graphite, the cubic form of boron nitride is less stable than its hexagonal form; however, the conversion rate between the two remains negligible at room temperature, similar to diamond. The cubic phase has a sphalerite crystal structure, also known as β-BN or c-BN.
Technical Properties:
| Property | Value |
|---|---|
| Compound Formula | BN |
| Molecular Weight | 24.82 |
| Appearance | Black solid in various forms |
| Melting Point | 2973 °C |
| Boiling Point | N/A |
| Density | 3.45 g/cm³ (c-BN) |
| Solubility in H₂O | Insoluble |
| Refractive Index | 1.8 (h-BN); 2.1 (c-BN) |
| Electrical Resistivity | 13 to 15 10x Ω-m |
| Poisson’s Ratio | 0.11 |
| Specific Heat | 840 to 1610 J/kg-K |
| Thermal Conductivity | 29 to 96 W/m-K |
| Thermal Expansion | 0.54 to 18 µm/m-K |
| Young’s Modulus | 14 to 60 GPa |
Preparation of Cubic Boron Nitride
Synthesis of c-BN follows methods similar to diamond production. Cubic boron nitride is created by treating hexagonal boron nitride under high pressure and temperature, analogous to producing synthetic diamond from graphite. Direct conversion occurs at pressures between 5 and 18 GPa and temperatures between 1730 and 3230 °C, similar to graphite-to-diamond conversion. Adding small amounts of boron oxide can reduce the required conditions to 4–7 GPa and 1500 °C. As with diamond synthesis, catalysts such as lithium, potassium, magnesium, their nitrides, fluoronitrides, water with ammonium compounds, or hydrazine can further reduce conversion requirements. Additional industrial methods, adapted from diamond growth, include crystal growth in a temperature gradient or explosive shock wave synthesis. The shock wave technique produces heterodiamond, a superhard compound of boron, carbon, and nitrogen.
Low-pressure deposition of c-BN thin films is also achievable. As with diamond growth, preventing hexagonal phase formation (h-BN or graphite) is essential. Hydrogen gas is used in diamond growth, whereas boron trifluoride is used for c-BN. Other techniques include ion beam deposition, plasma-enhanced chemical vapor deposition, pulsed laser deposition, reactive sputtering, and various physical vapor deposition processes.
Applications of CBN
Cubic boron nitride (CBN or c-BN) is extensively used as an abrasive. Its effectiveness is due to its insolubility in iron, nickel, and related alloys at high temperatures, unlike diamond, which dissolves in these metals. Polycrystalline c-BN (PCBN) abrasives are preferred for machining steel, while diamond is used for aluminum alloys, ceramics, and stone. At elevated temperatures, BN forms a protective boron oxide layer. Boron nitride also bonds effectively with metals through interlayers of metal borides or nitrides. Cutting tool bits commonly utilize c-BN crystals. In grinding applications, softer binders such as resin, porous ceramics, and soft metals are used, though ceramic binders are also compatible. Commercial products include “Borazon,” “Elbor,” and “Cubonite.”
Unlike diamond, large c-BN pellets can be produced by sintering—annealing c-BN powders in nitrogen just below their decomposition temperature. This sintering ability of c-BN and h-BN powders enables cost-effective production of large BN components. Similar to diamond, the combination of high thermal conductivity and electrical resistivity makes c-BN an excellent material for heat spreaders. Due to its low atomic mass and robust chemical and mechanical properties, c-BN is also widely used in X-ray membranes, offering low absorption and allowing the use of thin, durable films.
