What is PBN ceramic (pryolytic boron nitride)
PBN,
or pyrolytic boron nitride, is a highly pure ceramic material that exhibits
excellent chemical resistance and strength at high temperatures. This compound
is synthesized from boron and nitrogen and has good thermal conductivity. It is
widely used in making electrical insulators and cutting tools.
Production of PBN material
To
produce PBN, precise conditions are required due to its high purity of up to
99.99%. The manufacturing process involves a pyrolysis reaction carried out at
very high temperatures by chemical vapor deposition (CVD) of boron halides and
ammonia. Unlike hot-pressed boron nitride, the production of PBN through
chemical vapor deposition results in a uniform layer that gives it anisotropic
thermal conductivity. PBN (Pyrolytic Boron Nitride) is a ceramic material that
has a unique layered structure. Despite being a ceramic, its crystal structure
makes it not as prone to breakage or brittleness as other ceramics, and in some
ways similar to plastics, with a certain degree of elasticity. This unique
characteristic is due to the layered structure within PBN crystals that causes
interactions between its molecules, making PBN have higher toughness and
strength.
PBN ceramic parts' special structure
It
is important to differentiate between PBN's inter-layer atomic spacing and
intra-layer atomic spacing. Inter-layer atomic spacing refers to the space
between atoms in different layers, while intra-layer atomic spacing refers to
the space between atoms in the same layer.
PBN
has a hexagonal structure and is the most stable and softest crystalline form
of boron nitride ceramic. With each layer consisting of boron and nitrogen
atoms held together by covalent bonds, van der Waals forces bind the layers
within the structure instead.
The
production of Pyrolytic Boron Nitride (PBN) is carried out via the chemical
vapor deposition (CVD) process. As a result, for PBN crucibles, the crystals
within PBN crucibles adopt an orientation in line with the crucible walls. This
homogeneity ensures a consistent crystalline structure throughout the entirety
of the crucible. Consequently, there exists an equitably distributed thermal
conductivity profile. This feature is very advantageous for the production of
crystals and is very different from the crucibles obtained by machining hot
pressed BN. Moreover, during the CVD process, the materials that make up the
final product undergo multiple gas transformations and solid phase transitions.
The purity is far superior to that of ordinary boron nitride ceramics.
Therefore, PBN crucibles have become important tools for the manufacture of
high-purity crystals and become an important fundamental material for semiconductor
industry. QS Advanced Materials has years of experience supporting our industry with high quality PBN ceramic crucibles and other custom parts. A wide range of standard size PBN crucibles are prepared for your MBE and other advanced equipment.
Other
structures of boron nitride include cubic and wurtzite boron nitride. Cubic
boron nitride has a similar structure to that of diamond, while wurtzite boron
nitride has a structure comparable to Lonsdaleite.
Physical Properties of PBN ceramic
PBN's
physical properties include an ivory appearance, smooth surface, lack
of pores, no distinct odor, layered honeycomb appearance, a dielectric strength
at room temperature of 56 kV/mm, tensile strength of 153.84 N/mm2, elastic
modulus of 235690 N/mm2 and thermal shock resistance. Its strength increases
with temperature until reaching 2473 K, after which it decomposes into boron
and nitride at 3273 K.
Chemcial property of PBN
Chemically,
just like other hexagonal boron nitride, PBN is non-toxic and does not react
with acids, alkalis or salts at room temperature. However, it does corrode
slightly in lye and undergoes oxidation above 1273 K. As a result, most of
applications of PBN happens in vacuum or inert atomosphere.
In
conclusion, pyrolytic boron nitride is a high-quality ceramic material with
excellent properties that make it suitable for use in heaters and crucibles.
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