IN INCREASING THE STRENGTH OF PORCELAIN
N. A. Andreeva
and S. S. Ordan’yan
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 11, pp.2–5,November, 2002.
The effect of dispersity of rocky components on properties of porcelain is studied. Introduction of finely dis
persed components (quartz, feldspar) increases the mechanical strength of porcelain from 60 to 110 MPa and
produces no adverse effect on its electrical strength.
The ever-increasing demand placed on electric insulators
requires improvements to be brought about in both electro-
physical and mechanical properties of insulator porcelain. In
recent years, most engineering research  has been focused
on the use of porcelain as a structural material. The high
strength of electrical porcelain is usually attained by increas-
ing the percentage of alumina in it. However, using this
man-made material increases both the production cost and
the sintering temperature of porcelain mixtures. Therefore
considerable attention has been given to obtaining porcelain
with superior physicomechanical properties using conven
tional raw materials — kaolin, quartz sand, and feldspar.
In improving properties of insulator porcelain, the major
concern is reduction of internal structural stresses that are as
sociated mainly with the undissolved quartz. Recent studies
[2 – 7] provide grounds to believe that high-strength porce
lain capable of sustaining sharp variations in temperature
should contain a minimum amount of residual quartz. How
ever, even the total replacement of crystalline quartz by
(in alumina-based porcelain) does not completely
solve the problem. Large quartz particles get into the mixture
together with clay and kaolin in which the concentration of
may reach 20%. Viewed in this light, it was
thought of interest to study the effect associated with the size
of quartz grains brought in with plastic components on the
mechanical properties of sintered porcelain. Internal stresses
in the quartz-based porcelain arise, first, because of the dif
ference in thermal linear expansion coefficients of a-quartz
and the glassy phase and, second, because of polymorphic
transformation in silica. These stresses can be reduced sub-
stantially by decreasing dispersity of the initial and residual
quartz. On the other hand, quartz makes up part of the crys-
talline phases of porcelain that impart the needed mechanical
strength to engineering components. The more so, a consi-
derable part of quartz passes into molten feldspar, which in-
creases the strength of the glassy phase. As has been reported
in the literature [1, 2, 5], introduction of quartz of definite
grain composition (on average, 5 to 10 mm) produces a fa-
vorable effect on the strength of porcelain. Little (if any) is
known about the potential use of finer-grained porcelain,
which gives a stimulus to further research in the field.
In this work, we study the effect of initial quartz
dispersity on the structuring and main features of the precur
sor mixture and porcelain. We show that the mechanical
properties of porcelain can be improved by adding conven
tional rocky components (quartz sand, feldspar, broken por
celain) of high dispersity to the porcelain mixture.
A system of the following composition (wt.%) was used
in our study: 29 quartz sand, 19 feldspar, 5 broken porcelain,
and 47 clay + kaolin.
Mixtures differing in the dispersity of multiple rocky
components or a single component (quartz) were studied.
The rocky components were used as powders with their
dispersity varying in a wide range. The mean particle size
varied from 1 – 3 mm (for materials ground in a ball mill) to
30 mm (somewhat coarser in comparison to commercial ma
terials). The dispersity of components was determined by
sedimentation analysis and microscopy, and by an optical
method using a laser diffractometer.
Refractories and Industrial Ceramics Vol. 43, Nos. 11 – 12, 2002
1083-4877/02/1112-0325$27.00 © 2002 Plenum Publishing Corporation
St. Petersburg State Technological Institute (Technical Univer
sity), St. Petersburg, Russia.