Cubic Boron Nitride (c-BN) Nanopowder/Nanoparticles
Purity: 99.5%, Size: < 250 nm
Cubic boron nitride has a crystal structure analogous to that of diamond. While the cubic form is less stable than the hexagonal form, the conversion rate between the two is negligible at room temperature. The cubic form has a sphalerite crystal structure, also called 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 × 10^x 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
Cubic boron nitride is synthesized using methods similar to diamond production. Hexagonal boron nitride is treated at high pressure and temperature to convert it into the cubic form. Direct conversion occurs at pressures of 5–18 GPa and temperatures of 1730–3230 °C. Adding small amounts of boron oxide can lower the required pressure to 4–7 GPa and temperature to 1500 °C. Catalysts such as lithium, potassium, or magnesium (or their nitrides, fluoronitrides, or hydrazine) may also be used. Other methods include crystal growth in a temperature gradient or explosive shock wave techniques.
Low-pressure deposition of thin films of c-BN is possible. Methods include ion beam deposition, plasma-enhanced chemical vapor deposition, pulsed laser deposition, reactive sputtering, and other physical vapor deposition techniques. Boron trifluoride is often used to suppress growth of hexagonal phases.
Applications of Cubic Boron Nitride
Cubic boron nitride (c-BN) is widely used as an abrasive due to its insolubility in iron, nickel, and related alloys at high temperatures, making it suitable for machining steel. Polycrystalline c-BN (PCBN) abrasives are used for steel, while diamond abrasives are preferred for aluminum alloys, ceramics, and stone.
c-BN forms a passivation layer of boron oxide when in contact with oxygen at high temperatures. It binds well with metals through the formation of metal borides or nitrides. Cubic boron nitride is commonly used in cutting tool bits. For grinding, softer binders such as resin, porous ceramics, and soft metals are used, while ceramic binders are also applicable. Commercial products include “Borazon” (Diamond Innovations) and “Elbor” or “Cubonite” (Russian vendors).
Unlike diamond, large c-BN pellets can be produced by sintering c-BN powders in nitrogen at temperatures slightly below decomposition. This allows for cost-effective production of large BN parts. c-BN’s combination of high thermal conductivity and electrical resistivity makes it ideal for heat spreaders. Its low atomic mass and chemical robustness also make it suitable for X-ray membranes, enabling thin, low-absorption membranes with excellent mechanical properties.
