Boron Nitride ( BN ) - Supplier Data by Goodfellow

Background

Boron Nitride exhibits a hexagonal structure and is sometimes known as white graphite, due to its lubricity, anisotropic properties, heat resistance, and high thermal conductivity. This latter property, combined with a low thermal expansion, leads to excellent resistance to thermal shock.

All three forms, Hot Pressed, Pyrolytic and Hot Isostatic Pressed, can be used at very high temperatures. However, in an oxidising atmosphere the maximum use temperature is 850-900 °C.

Hot Pressed and Hot Isostatic Pressed Boron Nitride are produced by densification of powder, whereas Pyrolitic Boron Nitride is produced by Chemical Vapour Deposition (CVD), depositing onto graphite at temperatures in excess of 1800 °C.

Boron Nitride differs from graphite in having a high dielectric strength and low dielectric constant and is often used as an electrical insulator at very high temperatures.

Chemically inert, Boron Nitride is used as crucibles for molten metals. Boron Nitride is non-toxic and transparent to microwaves. It may be machined to close tolerances.

Key Properties

The key properties of Boron Nitride are tabulated below.

Table 1. Key properties

Chemical Resistance
Acids - concentrated Fair
Acids - dilute Fair
Alkalis Fair
Halogens Poor
Metals Good
Electrical Properties
Dielectric constant 4.3
Dielectric strength ( kV.mm-1 ) 40-200
Volume resistivity ( Ohm.cm ) 1011-1014 @ 25 °C
Mechanical Properties
Compressive strength ( MPa ) 30-120
Shear strength ( MPa ) 12-25
Tensile modulus ( GPa ) 20-35
Physical Properties
Apparent porosity ( % ) 2-15
Density ( g.cm-3 ) 1.9-2.2
Thermal Properties
Coefficient of thermal expansion ( x10-6 K-1 ) 1.0-36 @ 20-1000C
Specific heat ( J.K-1.kg-1 ) 800-2000 @ 25 °C
Sublimation point (°C ) 2600-2800
Thermal conductivity ( W.m-1.K-1 ) 15-50 @ 20 °C
Upper continuous use temperature (°C ) 950-2500

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