THE ROLE OF COMPONENT DISPERSITY AND MOLDING PRESSURE
IN THE MANUFACTURING TECHNOLOGY OF ELECTRIC PORCELAIN
N. A. Andreeva
and S. S. Ordan’yan
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 6, pp. 17 – 21, June, 2003.
The properties of porcelain produced by pressing mixtures containing aluminum oxide of different dispersities
are studied. Increasing the Al
dispersity and using the isostatic pressing technique provide a route to im
proving the performance characteristics of electric porcelain.
Improving performance characteristics of the electrical
porcelain involves the updating of its production technology.
The mechanical strength of porcelain can be enhanced by in-
troducing components such as alumina, zircon, and other
oxides that are capable of forming a crystal framework more
durable in comparison with mullite and quartz . The partial
or complete replacement of quartz by corundum (a-Al
results in a substantial improvement of the porcelain’s opera-
tional properties. Corundum contributes to the upgrading of
mechanical strength, corrosive resistance, electrical strength,
and dielectric loss tangent.
As is known, increasing the dispersity of the precursor
components of the porcelain mixture promotes substantially
the sintering process owing to the increase in surface area,
that is, the contact area of interacting particles. Following
this route, one can decrease the temperature of sintering and
thus obtain a material with uniform structure and improved
physicomechanical properties [2 – 7].
The average size of stone-hard particles in conventional
working mixtures of electrical porcelain (including the alu
mina-based porcelain) is 15 – 30 mm. The dispersity of
stone-hard components for Japanese high-strength alu
mina-based porcelain is substantially higher — more than
90% of the total of particles have a size less than 10 mm
across [3, 4].
On the other hand, the high dispersity of precursor com
ponents may adversely affect the fabricability of porcelain
mixtures. In plastic mixtures, the molding moisture content
tends to increase and the filtering ability becomes deterio
rated, which may cause strain in the preforms during drying
and thus impair the properties of the end product. Stone-hard
components with a higher degree of dispersity when used in
the pressure molding technology adversely affect the conso
lidation of powdered mixtures. This is due to the fact that the
difference in size between grains of the fine stone-hard frac-
tion and particles of the clay material (the filler) becomes
vanishingly small ; the resulting effect is the decrease in
density of both green preforms and sintered components.
In the traditional technology of porcelain production, a
mixture of stone-hard components is subjected to grinding,
which hinders a closer analysis of the effect of each indivi-
dual components on the properties of the porcelain.
Our goal in this work was to see to what extent the
dispersity of alumina and other stone-hard components
(mainly feldspar) may affect the properties of the alumina-
based electrical porcelain.
In today’s technologies, commercial alumina with an
average particle size of 10 – 15 mm are used for the fabrica
tion of electrical porcelain. We have used commercial alu
mina of the GK GOST 6912.1–29 grade (with an a-Al
content of 95% at least, as established by x-ray diffraction
analysis). The corundum material, because of its high hard
ness, is not easy to grind using conventional grinding bodies
made of corundum or uralite. The use of other grinding bodies
is undesirable because of possible contamination with extra
neous impurities. In our study we have used, along with a
ground commercial alumina, also corundum powders (grades
10M and 1M, with average particle size 10 and 1 mm across,
respectively) and an ultradisperse alumina with a particle
size of less than 100 nm deposited by a CVD plasma method.
A mixture of the following composition (wt.%) was
used: alumina, 25; feldspar, 24.3; broken porcelain, 6.6; clay
from the Novoraiskoe deposit, 26.4; clay from the Kysh
tymskoe deposit, 11; kaolin from the Prosyanovskoe deposit,
6.7 (the mixing formula borrowed from the Kornilovskii Por
celain Factory, St. Petersburg, Russia).
Refractories and Industrial Ceramics Vol. 44, No. 4, 2003
1083-4877/03/4404-0277$25.00 © 2003 Plenum Publishing Corporation
St. Petersburg State Technological Institute (Technical Univer
sity), St. Petersburg, Russia.