CERAMIC ITEM DEFORMATION DURING FIRING:
EFFECTS OF COMPOSITION AND MICROSTRUCTURE (REVIEW)
D. V. Andreev
and A. I. Zakharov
Translated from Novye Ogneupory, No. 8, pp. 45 – 52, August, 2009.
Original article submitted May 22, 2009.
The scope is considered for increasing the high-temperature stability to deformation in ceramic items as re
gards comprehensive improvement in characteristics corresponding to current economic trends.
Keywords: porcelain, deformation, buckling, high temperature, firing, sintering, viscosity, quartz, mullite.
It is becoming increasingly important to examine defor
mation during firing for molded semifinished products made
of materials sintered at high temperatures and subsequently
acquiring a vitrocrystalline nature, particularly on account of
the tendency to reduce the firing times and temperatures by
the use of suitable additives, and also in connection with
tightening specifications for the size accuracy. Large ceramic
products such as drainage pipes may be reduced in mass by
reducing the wall thickness, which reduces the amount of
raw material used and the energy consumption, but then
there is an increase in the tendency of the semifinished prod-
uct to pyroplastic deformation.
Researches have been done on a large scale on the creep
in ceramics at high surface temperatures, but they have not
been focused on the deformation in multicomponent systems
such as porcelain during firing . The variety of composi
tions and firing modes must determine the substantial differ
ences in deformation . It is not always possible to extend
the phenomenology of deformation for materials whose ele
mentary rheological properties differ substantially to other
materials characterized by more complicated behavior. One
approach is to examine porous vitrocrystalline material such
as porcelain during firing, whose behavior is represented by
a very complicated set of properties.
The task of giving a proper description of deformation
splits up into several very complicated subtasks: determina
tion of key parameters of the structure and composition, the
changes in them during firing under load, the effects on the
deformation, determination of the effects of firing conditions
and shape of a component on processes, and this combines
with the choice or creation of rheological models and soft
ware for calculating the deformation from the significant pa
The chemical and mineral compositions had the main ef-
fects on the deformation at high temperatures. Although
there are many forms of porcelain, one can distinguish in
their compositions the quartz component, whose grains are
rarely greatly altered during firing, and which only partially
dissolve in the liquid, together with the clay-mineral compo-
nent and the fluxes, which form a liquid at a high tempera-
ture. One can control the properties of the porcelain, includ-
ing the deformation behavior on firing, by adjusting the
nature, grain size, and method of preparation for those com-
It is simplest to regulate the properties of a porcelain by
varying the contents of low-activity crystalline phases: the
oxides of silicon, aluminum, zirconium , and so on. One
needs to consider not only the grain size but also the firing
conditions, since the amounts of the crystalline phases may
be reduced substantially by prolonged hold. There has been a
study  of the reactions between porcelain components
with model feldspar liquid, which has shown that in firing of
duration 12 h with a hold of1hintheoven with electrical
heaters the oxide of aluminum (0.83 mm) is almost insoluble
in the feldspar liquid up to 1350°C, while the quartz (2.8 mm)
dissolves to the extent of 10% of the initial material. On
more prolonged heating in a gas-flame furnace, the amount
of dissolving quartz was not more than 35%, or corundum
5%. The solubility of mullite formed in a mixture of
metakaolinite with feldspar was high in both forms of firing.
It has been found  that the pyroplastic deformation in
creases as the dissolution of the quartz in the glass phase in
creases and as the ratio of the length of the mullite crystals to
their diameter decreases.
Refractories and Industrial Ceramics Vol. 50, No. 4, 2009
1083-4877/09/5004-0298 © 2009 Springer Science+Business Media, Inc.
Mendeleev Russian Chemical Engineering University, Moscow,