THE EFFECT OF A SINTERING METHOD ON THE PROPERTIES
OF HIGH-TEMPERATURE CERAMICS
S. N. Sannikova,
T. A. Safronova,
and E. S. Lukin
Translated from Novye Ogneupory, No. 10, pp. 26 – 29, October, 2006.
Original article submitted July 12, 2006.
A combined application of oxide and oxygen-free high-melting compounds in ZrN – ZrB
raises the oxidization resistance of the oxygen-free components in the system. The use of hot compaction for
sintering ceramics produced from composite materials makes it possible to achieve 98% of the theoretical
density, which is especially important for very hard materials, where the presence of defects perceptibly
lowers the real strength parameters. A high density and the absence of open porosity on the surface of compo
site ceramics allows for a full use of the high-temperature potential of high-melting, oxygen-free compounds
in thermally stressed service conditions.
Available published data on composite materials based
on high-melting compounds of different classes indicate the
possibility of developing high-temperature materials with
preset properties. However, the overwhelming majority of
heterophase materials based on oxygen-free compounds are
thermodynamically nonequilibrium, which restricts the re-
source of their high-temperature and strength parameters.
We have used zirconium dioxide to increase the thermo-
dynamic stability of oxygen-free compounds ZnN (T
= 2980°C) and ZrB
= 3090°C) characterized by the
trend of increasing high-temperature strength, high elasticity
modulus, and microhardness . The usual sintering meth
ods are unable to compact composite ceramics based on co
valent compounds, due to a low diffusion mobility of the
components when sintered in vacuum at or above 1800°C
. To consolidate and strengthen the ZaN – ZrB
system, we have used the method of hot compaction, which
is widely used in ceramic technology to produce high-den
sity materials based on different components, including com
pounds with a high degree of covalence of chemical bonds.
To obtain a homogeneous microstructure, whose relative
uniformity is maintained at any high-temperature application
conditions, one should use initial powders with an equal size
of particles, preferably spherically shaped. The nearer the
particle distribution in the initial powder to a monofractional
distribution, the more homogeneous the structure and proper
ties of the resulting ceramics.
Recently, chemical methods have become widely used to
produce powders with a controllable structure. Thus, it is
possible to obtain particles of a required shape and a uniform
distribution of modifying additives . The method of chem-
ical precipitation has been used to obtain highly disperse ZrO
powder partly stabilized by 5.34 wt.% Y
. In view of the
very small particle size (<1 ìm) produced by chemical pre-
cipitation, strong intramolecular bonds are soon formed, and
the emerging particles of ZrO
powder are low-aqueous and
crystal-like, and have a spherical shape.
The nature and intensity of interaction between the initial
components significantly depend not only on their dispersion
but also on their homogeneity after mixing. The simplest and
most common method for producing multicomponent ceram
ics is based on simultaneous milling and mixing of powders.
A multicomponent batch of composition ZrN – ZrB
was prepared by joint milling in ethanol in a Pulveri
sette 6 planetary mill produced by Fritsch. The initial compo
nents were zirconium nitride powder (TU 6-09-4050) and
zirconium boride powder (TU 09-03-46) produced by the
Donetsk Chemical Reactant Works. The powder particle size
after milling was1–1.5ìm .
Brittle destruction of particles occurs as a result of the
emergence and accumulation of inner stresses exceeding the
strength of the material. Microscopic analysis indicates that
extending the milling duration from 10 to 30 min with a
drum rotational speed of 600 rpm does not perceptibly in
crease the degree of dispersion. Such a mechanical impact is
presumably insufficient for inducing microplastic deforma
tions and accumulating defects in the monolayers of the crys
Refractories and Industrial Ceramics Vol. 47, No. 5, 2006
1083-4877/06/4705-0299 © 2006 Springer Science+Business Media, Inc.
Kompozit JSC, Korolev, Moscow Region, Russia; D. I. Mendele
ev Russian Chemical Engineering University, Moscow, Russia.