BORON AND SILICON NITRIDES
AS MECHANICAL ENGINEERING CERAMICS
A. P. Garshin
Translated from Novye Ogneupory, No. 9, pp. 35 – 40, September 2009.
Original article submitted May 10, 2009.
Contemporary ideas are given about the structure, chemical bonding, preparation methods and main technical
characteristics of boron and silicon nitrides, and also ceramic materials based on them. Areas are considered
for application of BN- and Si
-ceramics in engineering and other fields of technology.
Keywords: boron nitride, silicon nitride, nitride ceramics, mechanical engineering ceramics, ceramic engines,
ceramic cutting tool, abrasive tool.
Ceramics relate to materials prepared by sintering min-
eral and synthetic inorganic substance powders . There are
various oxide ceramics, i.e. aluminosilicate (based on
), mullite-corudnum (Al
forsterite (2MgO × SiO
), celsian (BaO × Al
carbide (based on SiC, B
C, etc.), nitride (based on BN, AlN,
, etc.), silicide and boride (based on transition metal
silicides and borides), and also halogenide (based on
halogenides of alkalis and alkaline-earth metals).
Production technology for ceramics includes powder
preparation, preparing them by means of adding organic
binders and plastifiers of a plastic mix, from which an object
is molded by compaction, casting, extrusion, etc. Molded ob
jects are dried, the organic binder is removed from them by
low-temperature firing, and then objects of the required den
sity and phase composition are prepared by sintering at high
For engineering ceramics there are typically high values
of elasticity modulus, melting temperature (decomposition,
sublimation), hardness, chemical stability and strength at
high temperature. Due to these properties engineering ceram
ics in contrast to artistic, sanitary engineering, building, re
fractory, electronic, electrical engineering, radio ceramics
and bioceramics, for which as a rule only one or two of these
properties is required, necessitate a more complex, improved
and therefore more expensive production technology.
A leader in the production and sale of engineering ceram
ics is Japan, that supplies the world market with 25 – 30% of
ceramic objects for engineering, including 48 – 50% of ob-
jects manufactured for ceramic engines and about 20% for
ceramic cutting tools (ceramic cutters, milling tools, etc.). a
visible position among ceramic objects used in engineering
is occupied by boron and silicon nitrides, used mainly in
manufacturing cutting tools for machining various metals, al-
loys and non-metallic materials (glass, glass ceramic, gran-
ite, etc.) and wear-resistant and heat-resistant elements in gas
turbines, automobile engines, etc.
STRUCTURE OF BORON AND SILICON NITRIDES
Currently boron nitride is known in the form of three in
dependent modifications: hexagonal (graphitic) BN
and hexagonal wurztitic BN
as the starting material for synthesis of the BN
The hexagonal modification of boron nitride, the same as
for graphite, relates to a class of compounds of a layered
structure. Within a layer each boron atom is surrounded by
three nitrogen atoms and each nitrogen atoms is surrounded
by three boron atoms. The length of the bond between boron
and nitrogen atoms is 0.1446 nm, and the angle between
bonds is 120°. Each layer in the BN
structure consists of
regular flat six-membered rings (Fig. 1a ), similar to graphite
(Fig. 1c) or a benzene ring. The distance between the planes
of layers is 0.333 nm, and the layers themselves in contrast to
the structure of graphite, boron and nitrogen atoms alternate
with each other and arranged precisely above each other
(Fig. 1a ). in layers the chemical bond between nitrogen and
boron atoms is covalent (directional) and between layers it is
Refractories and Industrial Ceramics Vol. 50, No. 5, 2009
1083-4877/09/5005-0363 © 2009 Springer Science+Business Media, Inc.
St. Petersburg State Polytechnic University, St. Petersburg, Russia.