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Boron Nitride (BN) - Properties and Information on Boron Nitride

Boron nitride (BN  is a synthetic material, which although discovered in the early 19th century was not developed as a commercial material until the latter half of the 20th century. Boron and nitrogen are neighbours of carbon in the periodic table - in combination boron and nitrogen have the same number of outer shell electrons - the atomic radii of boron and nitrogen are similar to that of carbon. It is not surprising therefore that boron nitride and carbon exhibit similarity in their crystal structure.

In the same way that carbon exists as graphite and diamond, boron nitride can be synthesised in hexagonal and cubic forms.

The synthesis of hexagonal boron nitride powder is achieved by nitridation or ammonalysis of boric oxide at elevated temperature. Cubic boron nitride is formed by high pressure, high temperature treatment of hexagonal BN.

Hexagonal boron nitride (h-BN) is the equivalent in structure of graphite (see figure 1). Like graphite its plate like microstructure and layered lattice structure give it good lubricating properties. h-BN is resistant to sintering and is usually formed by hot pressing.


h-BN powder

Figure 1. h-BN powder (photo courtesy of Ceram Research Ltd)


Cubic boron nitride (C-BN) has the same structure as diamond and its properties mirror those of diamond. Indeed C-BN is the second hardest material next to diamond. C-BN was first synthesised in 1957, but it is only in the last 15 years that commercial production of C-BN has developed.

Key Properties

Hexagonal Boron Nitride (h-BN)

h-BN has excellent lubricating properties

In the hot pressed state, h-BN is readily machinable using conventional metal cutting techniques, hence complex shaped components can be fashioned from hot pressed billet.

Providing oxidation of the surface can be prevented, h-BN is not wetted by most molten metals, glasses and salts and hence has a high resistance to chemical attack.

High dielectric breakdown strength

High volume resistivity

Good chemical inertness

Cubic Boron Nitride (C-BN)

C-BN is the second hardest material known, inferior only to diamond

High thermal conductivity

Excellent wear resistance

Good chemical inertness

Table 1. Typical properties for hexagonal and cubic boron nitride.

Property h-BN C-BN
Density (g.cm-3) 2.3 2.2
Melting Point (°C) 3000 (dissociates)  
Hardness (Knoop 100 g) (kg.mm-1) 400  
Modulus of Rupture (MPa) 100 (ll to press dir)
50 (⊥ to press dir)
Youngs Modulus (MPa) 20 - 103  
Thermal Expansion Co-eff (RT-1000 °C - x10-6) (°C-1) 1 (ll to press dir)
4 (⊥ to press dir)
Thermal Conductivity (W/m.K) 20 (ll to press dir)
27 (⊥ to press dir)
Dielectric Breakdown Strength (kV.mm-1) 35  
Dielectric Constant   4.1
Vol Resistivity (ohm.cm) 108 - 1013  


Note: Data for h-BN were taken from a hot pressed sample. As this is a highly directional forming process, properties are anisotropic i.e, differ in directions relative to the pressing direction. For this reason, some values are higher than those reported in the attached property table.


Electrical insulators

The combination of high dielectric breakdown strength and volume resistivity lead to h-BN being used as an electrical insulator however its’ tendency to oxidise at high temperatures often restrict its use to vacuum and inert atmosphere operation.

Crucibles and reaction vessles

Its chemical inertness leads to application as thermocouple protection sheaths, crucibles and linings for reaction vessels though as above oxidation must be avoided.

Moulds and evaporating boats

h-BN is used in bulk form or as a coating for refractory moulds used in glass forming and in superplastic forming of titanium (see figure 2). It is also used as a constituent in composite materials e.g. TiB2/BN composites for metal evaporation boats, and Si3N4/BN for break rings in continuous casting of steel (see figure 3).

Crucible and boat for molten steel

Figure 2. Crucible and boat for molten steel (photo courtesy of Ceram Research Ltd)

Breakrings for horizontal continuous casting of steel

Figure 3. Breakrings for horizontal continuous casting of steel (photo courtesy Ceram Research Ltd)

Hot isostatic pressing

Its refractoriness combined with the fact that it is not wetted by molten glass lead to h-BN being used in the production of hot isostatically pressed (HIP’ed) material, most notable ceramics. In this application preformed parts are coated in h-BN prior to glass encapsulation and HIP’ing. This protects the part being HIP’ed from actually coming into contact with the glass, which in turn makes it easier to remove after HIP’ing.

Machine cutting tools and abrasives

Cutting tools and abrasive components particularly for use with low carbon ferrous metals have been developed using C-BN. In this application the tools behave in a similar manner to polycrystalline diamond tools but can be used on iron and low carbon alloys without risk of reaction.

Substrates for electronic devices

C-BN is used for substrates for mounting high density and high power electronic components where the high thermal conductivity achieved allows efficient heat dissipation.

Wear resistant coatings

Due to its high hardness and excellent wear resistant properties, coatings of C-BN have been developed.




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  1. June Marie Bassett June Marie Bassett United States says:

    How does boron nitride affect skin, used in makeup products? Is it a carcinogen?

  2. Bayram Punar Bayram Punar Turkey says:

    ı study about graphite furnace I use boron nitride solids for electrical isolator. I've learned that Boron nitride resistivity change with temperature I have problems upper 1800 degree
    Boron nitride can be contuctor in these degrees if you have any information about this sitution can you help me

    • Oswald Wang Oswald Wang United States says:

      Hi, Kevin from PENSC. I export BN sleeve to Turkey more. As you said, I think it`s problem with BN consistency, the produce technology is different from PENSC to others.

  3. Giridhar Naidu Giridhar Naidu India says:

    Hello in silivering plastic or fibreglass is boron used in clear coat to eleminate the yellowing and give it a chrome like finish ?

  4. Fereshteh Hojatisaeidi Fereshteh Hojatisaeidi United Kingdom says:

    Which porosity and structure of BN has a significant contribution for gas adsorption?

  5. Fereshteh Hojatisaeidi Fereshteh Hojatisaeidi United Kingdom says:

    Which porosity and structure of BN has a significant contribution for gas adsorption?

  6. Abin John Abin John India says:

    what about BN thermal shock properties above 1900K

  7. Mark Dawson Mark Dawson United Kingdom says:

    Where can I by a small quantity to recoat some grinding wheels?

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of AZoM.com.

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