Boron Nitride

What is Boron Nitride (BN)?

Boron nitride (BN) is a compound of boron and nitrogen, often called white graphite or inorganic graphene due to its layered structure and unique properties. Boron Nitride ceramic products are generally categorized into two main types based on the manufacturing process: Hot-Pressed Boron Nitride (HPBN) and Pyrolytic Boron Nitride (PBN).

HPBN is known for its excellent machinability, high thermal stability, and electrical insulation, making it ideal for crucibles, insulators, and vacuum components. PBN, produced via chemical vapor deposition, is characterized by high purity, gas-tightness, and resistance to thermal and chemical corrosion—perfect for semiconductor and crystal growth applications. Custom sizes and shapes of BN products are available upon request at Stanford Advanced Materials.

Key Structural Forms of Boron Nitride

Before diving into the structural details, here's a quick comparison of key material properties across BN forms:

a) Hexagonal Boron Nitride (hBN)

Known as "white graphite" due to its layered hexagonal structure, hBN shares softness and lubricity with graphite. However, it also functions as an excellent electrical insulator with high thermal conductivity, making it ideal for:

• High-temperature lubricants and mold release agents.
• Thermal management materials in electronics.
• Vacuum furnace components and insulators.

b) Cubic Boron Nitride (cBN)

Isoelectronic with diamond, cBN offers comparable hardness with superior thermal and chemical stability. These properties make cBN an excellent choice for:

• Abrasives and cutting tools.
• Oxidation-resistant coatings.
• High-performance components in extreme environments.

c) Wurtzite Boron Nitride (wBN)

An extremely rare and high-pressure phase, wurtzite boron nitride (wBN) is believed to surpass even diamond in hardness under certain conditions. Although its synthesis is challenging, its unique structure enables potential use in:

• Research into superhard materials.
• Specialized applications require ultra-high hardness and pressure resistance.
• Advanced protective coatings (experimental stage).

d) Amorphous Boron Nitride (aBN)

The non-crystalline counterpart to structured BN forms, aBN, lacks long-range order and resembles amorphous carbon. It is used in specialized applications where a uniform, structureless coating or filler is needed:

• Dielectric coatings.
• Non-structured thermal insulation.
• Functional fillers in polymer composites.

Comparison Articles:

HPBN vs. PBN

HBN, CBN, and WBN

Manufacturing Process

Boron nitride starts with common precursors: boric acid or boron oxide for the boron, and a nitrogen source like ammonia or urea. These react to form amorphous BN (aBN), a non-crystalline intermediate that sets the stage for more specialized structures.

Hexagonal BN (hBN): made by heating aBN in an inert atmosphere—usually around 900°C—until the material reorganizes into a layered, graphite-like structure. The result: a soft, white ceramic that handles heat well and doesn't react easily with other materials.

Cubic BN (cBN): through high-pressure and high-temperature synthesis, similar to synthetic diamond production. The result is one of the hardest known materials, used where cutting and wear resistance are everything.

Pyrolytic BN (P-BN): comes from chemical vapor deposition (CVD), a process that builds the material layer by layer in vacuum conditions. This produces a dense, ultra-pure ceramic with strong directional properties—commonly used in electronics and thermal shielding due to its purity and stability.

The next step is shaping it into usable parts. That depends on the form and the final application.

• Hot pressing fuses the powder under heat and pressure, producing strong, dense components used in demanding environments.
• Cold pressing, followed by sintering, is more cost-efficient but doesn’t reach the same density.
• Injection molding allows for complex shapes using a binder that’s later burned off before final firing.
• For P-BN, shaping happens during the CVD process itself, offering tight control over thickness and geometry right from the start.

Material Advantages

• Thermal Management: High thermal conductivity and exceptional heat dissipation.
• Electrical Insulation: Low dielectric constant and high dielectric strength.
• High Temperature Resistance: Stable at temperatures exceeding 2000°C in inert atmospheres.
• Machinability: Easily shaped into custom forms with precise tolerances.
• Chemical Inertness: Resistant to most chemicals and oxidation, making it reliable in harsh environments.
• Non-Wetting: Ideal for molten metal and glass applications.

Industrial Applications of Boron Nitride

Others you may want to know about boron nitride

1. Does boron nitride conduct electricity?

No. BN—especially in its hexagonal form—is an excellent electrical insulator. Unlike graphene, BN doesn’t support electron flow due to its wide bandgap. That's why it's often used in dielectric layers, substrates, and high-voltage environments.

2. Why is BN used in cosmetics?

Boron nitride provides a silky, smooth texture that facilitates the even application of cosmetic products. It also diffuses light well, creating a soft-focus effect that reduces the appearance of fine lines and pores. Its oil-absorbing properties make it popular in powders and foundations.

3. Is boron nitride toxic to humans?

BN is generally considered non-toxic and safe for handling. It’s chemically stable and doesn’t react easily with skin or tissue. However, like with many fine powders, inhalation of airborne particles should be avoided. Proper dust control is important in industrial settings.

4. What happens when boron nitride is heated?

BN has excellent thermal stability. Hexagonal BN can withstand temperatures above 900°C in air and over 1,800°C in inert or reducing atmospheres. It doesn’t oxidize easily, and when heated, it maintains structural integrity better than many ceramics.

5. Can a BN plate stop bullets?

Not in its current form. While BN materials—especially in cubic or nanotube forms—have very high strength, they’re typically not manufactured or structured like ballistic armor. Their hardness and thermal properties are impressive, but their bullet-stopping ability depends on thickness, layering, and composite design.

6. Can boron nitride withstand acid?

Hexagonal boron nitride is chemically inert to most acids at room temperature. However, it can slowly react with hot, concentrated acids. Its resistance makes it a suitable material for chemical handling, crucibles, and seals in corrosive environments.

Boron Nitride Video