A STRUCTURAL STUDY OF Y
E. A. Korableva,
V. S. Yakushkina,
O. S. Grishin,
V. V. Vikulin,
and O. P. D’yachenko
Translated from Novye Ogneupory, No. 10, pp. 56 – 59, October, 2004.
Original article submitted August 28, 2004.
Partially stabilized zirconia ceramics ZrO
) of different structures and phase compositions are tested
for thermal stability and thermal shock. The ceramics can be used as solid electrolytes in oxygen activity sen
sors for fluid heat transfer agents (lead).
Ceramics based on partially stabilized zirconium dioxide
(PSZD) exhibit a unique combination of physicomechanical
and electric properties: high strength and fracture toughness,
resistance to corrosive attack, low heat conductivity, and
anionic conduction. An intrinsic property of PSZD-based
materials is the temperature-controlled co-existence of three
phases: monoclinic (a), tetragonal (b), and cubic (g), which
makes it possible to design new materials with a unique com-
bination of properties.
Availability of high-strength and tough materials based
on PSZD with stabilizing agents added (MgO, CaO, Y
CeO) made it possible to use sophisticated and expensive
technologies — such as cold isostatic pressing (CIP) and hot
isostatic pressing (HIP) for shaping ceramic components
[1 – 3]. It was shown that high-strength and high-toughness
ceramic materials lack sufficient stability under thermome
chanical loading conditions and resistance to thermal shock.
This narrows down substantially the choice of suitable ce
ramics for operation under transient temperature conditions,
for example, in self-heating of heavy-duty friction couples,
or at high temperatures (500 – 1700°C), in solid electrolytes
exposed to hot gases or molten metals. The service life of
such friction couples and solid electrolytes is determined
by their physicomechanical properties and, consequently,
microstructure and phase composition of the ceramics used.
Increasing the thermal stability of PSZD-based ceramics
involves the design of an optimal structure and a specified
phase composition for particular service conditions.
Our goal in this study was to gain an insight into struc
tural features responsible for thermal stability of a high-den
sity ceramics based on PSZD – Y
for solid electrolytes
operationally exposed to molten metals (lead or copper) and
High-density ceramic materials differing in structure and
composition were studied. The precursor materials were
powders synthesized by the method of chemical precipitation
from solutions of zirconium and yttrium chlorides. The pow-
ders were composed of spherical particles of size 25 – 40 nm
aggregated into formations less than 2 mm across. This parti-
cle morphology allows the use of a conventional shaping
method — thermoplastic injection molding. The final
sintering was carried out in air at 1450 – 1700°C. The test
specimens had dimensions of 7 ´ 7 ´ 70 mm; the solid elec
trolytes were shaped as test tubes of diameter 15 mm and
length 24 mm.
Four types of high-density ceramics of different structure
and phase composition were considered:
T — tetragonal polycrystalline PSZD (3 mol.% Y
with a fine-crystalline structure, high strength, and high frac
TT — polycrystalline PSZD (3 mol.% Y
), with a
transformed (t ¢) tetragonal phase, which is obtained from the
sintered cubic phase through rapid quenching to a tempera
ture at which the t ¢-phase precipitates;
MK — PSZD-based ceramic material prepared from a
mixture of powders stabilized by 1 – 8% Y
taken at a ra
tio of 1.5 : 1. The final chemical composition of this material
after sintering is PSZD (3 mol.% Y
K — ceramic material based on the fully stabilized
– 8 mol.% Y
, composed of crystalline grains (cubic
phase). Currently, the material has been recommended for
Refractories and Industrial Ceramics Vol. 46, No. 1, 2005
1083-4877/05/4601-0021 © 2005 Springer Science+Business Media, Inc.
Tekhnologiya Research and Production Enterprise (Tekhnologiya
RPE), Obninsk, Kaluga Region, Russia.