A MACROSTRUCTURAL MODEL OF LAMINATED CERAMIC
WITH ENHANCED THERMAL RESISTANCE
A. A. Frolov
Translated from Novye Ogneupory, No. 9, pp. 52 – 55, September, 2004.
Original article submitted June 24, 2004.
A macrostructural model of laminated ceramic consisting of a fragmented base composed of blocks cemented
with a protective coating layer is proposed. Based on this model, components with enhanced heat resistance can
be prepared owing to the relaxed thermal stress and matched temperature expansion coefficients. Refractory
rings with a fragmented base from quartz ceramic and Nb
two-sided protective coating and tubular compo
nents assembled from these rings show a higher thermal stability than their analogs with a monolithic base.
Engineering components from laminated ceramics have
found application in industry in the fabrication furnace
chambers or containers that are used in the thermochemical
treatment of high-purity compounds for protection against
environmental contaminants. During service, ceramics are
subjected to thermal cycling under load, and thermal stabi-
lity, that is, the ability of ceramics to sustain temperature
changes at a rate of ten or a hundred degrees per minute to
reach 1000°C or higher, is a major property that determines
their working capacity.
The thermal stability of a particular ceramic component
is controlled by the thermal stability of the ceramic material
as well as by the component’s size and shape. The thermal
stability is conventionally characterized by thermal stability
criteria and size and shape factors . In components fabri
cated from laminated ceramics, one of the major factors criti
cal to the failure is stress arising from the difference in the
coefficients of linear thermal expansion (CLTE) of laminate
materials. In this paper, we consider ways that may lead to
relaxation of thermal stresses in ceramic laminates with a
two-sided protective coating.
In this work, our special concern is to consider ways to
wards increasing the thermal stability of cylindrical compo
nents made from quartz ceramic with a two-sided niobium
pentaoxide coating intended for high-temperature treatment
of high-purity Nb
OF THE ADOPTED MODEL
As a rule, thermal stability is assessed by comparing the
number of thermal heat-and-cool cycles that components or
specimens, tested under identical conditions, are capable of
sustaining prior to visible damage or failure. To characterize
the thermal stability of ceramic materials, thermal stability is
widely used. Quite a number of criteria (some 20 or more)
have been proposed for evaluating the efficiency of materials
operating under different service conditions . In the pres
ent work, a thermal stability criterion R is used which is de
termined by the destructive radial temperature gradient for
standard ring specimens.
The thermal stability criterion for a laminated specimen
can be written in the form
R = DT
where R is the average criterion of thermal stability, DT
the radial temperature gradient responsible for the failure of
a standard ring specimen, and S
is a coefficient dependent
on the shape and size of the laminated specimen (an inverse
of the factor parametrizing the shape and size ).
A cylindrical component may be considered as a ring
with a height larger than the diameter, and the difference in
thermal stability of a standard specimen and a cylinder can
be accounted for by a factor S
, somewhat different in value
). For a component shaped as a parallelepiped, the for
Refractories and Industrial Ceramics Vol. 45, No. 6, 2004
1083-4877/04/4506-0450 © 2004 Springer Science+Business Media, Inc.
I. N. Frantsevich Institute for Problems of Materials Science, Na
tional Academy of Sciences, Kiev, Ukraine.