CONTROL OF THE STRUCTURAL AND PHASE CHARACTERISTICS
OF RAW MATERIALS IN THE TECHNOLOGY OF FINE CERAMICS
E. I. Evtushenko,
I. Yu. Moreva,
O. K. Sysa,
V. I. Bedina,
and E. M. Trunov
Translated from Novye Ogneupory, No. 12, pp. 9 – 10, December, 2010.
Original article submitted September 9, 2010.
Questions related to the preparation and control of the properties of raw materials from the standpoint of struc
tural instability are considered. It is demonstrated that the use of the technology of artificial ceramic binders
for the production of fine and technical ceramics and high-alumina refractories is showing promise.
Keywords: structural instability, hydrothermal treatment, thermal and mechanical activation, artificial ce
With the significant growth in the production of fine ce-
ramic articles, the requirements that are imposed on the qual-
ity of the articles have now become more exacting. In addi-
tion, reserves of high-quality natural rawmaterials is being
exhausted. The presence of soluble and insoluble impurities,
structural irregularities and the instability of the properties of
clay stock have together made the production process more
complicated and led to a growth in production rejects.
In a number of cases the influence of irregularities in the
crystalline lattice and structural instability may become one
of the most significant factors governing the rheotechnolo
gical properties of disperse systems and aspects of the forma
tion of articles, and as a consequence, the quality of the ce
ramic. The degree of ordering of the crystalline structure of
clay minerals plays an exceptionally important role in the
manifestation of the physico-chemical properties of these
minerals . Thus, for example, irregularities in the crystal
line lattice of Zhuravlinolog kaolin make it unstable in cast
ing production procedures .
Such imperfections may be eliminated with the use of
various technological techniques that involve action in a dis
perse medium as well as the structure and phase composition
of the solid phase. Thus, with the use of thermal and mechan
ical activation it becomes possible to substantially alter the
properties of the rawmaterials and the behavior of these ma
terials in the production cycle as well as the characteristics of
the finished articles .
The rate of structural changes is related to the mobility of
defects and in the general case is a function of stresses and
temperature. Stresses may be internal, associated with the
concentration basically of nonequilibrium defects, or exter-
nal, arising in the course of mechanical action (grinding,
kneading, etc.). Structural changes accelerate with an in-
crease in temperature as well as under conditions defined by
the action of the Rebinder and Hedwall effects [3, 4]. One of
the most intensive methods of affecting the structure of clay
is hydrothermal treatment of the material [5, 6]. This method
assures rapid stabilization of structure in the course of sev
eral dozen minutes, comparable with that achieved in months
and years with natural treatment. It also makes it possible to
reduce by nearly 90% the energy of the interaction between
the particles in the suspensions and, as a consequence,
achieve a high degree of yield of the casting slip practically
without the use of addition agents or electrolytes. or with
only minimal quantities of such agents and electrolytes .
Wet grinding is another excellent and well-known
method of stabilization of structure. The method leads to pre
ferred dispersion in the most highly deformed sectors and a
decrease in the internal energy of the particles as a conse
quence of the Rebinder effect, though at the same time there
occurs an increase in surface energy. Steps aimed at addi
tional stabilization of the slips often must be performed to
decrease the interaction energy between the particles and im
prove the rheotechnological properties of the suspensions
following wet grinding. These steps include ageing (some
times for several days, since the rate of structural alteration
and relaxation of residual or added stresses is relatively high)
Refractories and Industrial Ceramics Vol. 51, No. 6, March, 2011
1083-4877/11/5106-0397 © 2011 Springer Science+Business Media, Inc.
Shukhov State Technological University, Belgorod, Russia.