EFFECT OF CERAMIC POWDER FINENESS
ON MULLITE-ZIRCONIUM CERAMIC PROPERTIES
G. P. Sedmale,
A. V. Khmelev,
and I. É. Shperberga
Translated from Novye Ogneupory, No. 1, pp. 41 – 46, January 2011.
Original article submitted October 29, 2010.
Results are provided for a study of the development of high-temperature mullite-zirconium ceramic with use
of activated ceramic powders prepared by grinding for different times with addition of illite clay, and from
pure oxide powders. It is shown that increased activity and amorphicity of ground particles considerably pro
motes formation of mullite phase at 1200°C, and also transition of the monoclinic modification of ZrO
tetragonal, particularly with an increase in firing temperature. It is proposed that as a result of rapid “freezing”
the structure retains the high-temperature modification of ZrO
, having a tendency with slow ceramic cooling
to transform into the monoclinic modification.
Keywords: mullite-zirconium ceramic, illite clay, grinding, particle size.
Mullite-zirconia (mullite-corundum) ceramic is one of
the materials used extensively in high-temperature produc-
tion processes. A distinguishing feature of mullite-zirconia
ceramic is the retention of high strength, including at ele-
vated temperature and with temperature falls. The set of
these properties predetermines further application of the ce
ramic and use of it in high-temperature production processes.
It has been established  that mullite-zirconia ceramic
may be prepared from mixed starting compositions, includ
, silica-gel, ZrO
with addition of
7.75 – 8.75 wt.% illite clay, promoting sintering and forma
tion of a mullite phase at lower temperatures . On the
other hand, the importance is indicated in [3, 4] of the degree
of grinding of the starting powders. It has been established
grinding ceramic powders leads to destruction of the particle
crystal lattice, and as a consequence to amorphization. Here
higher sintering indices are achieved for ceramic material
and correspondingly density, and ultimate strength in bend
ing and compression. However, a distinguishing feature of
rapid grinding  is formation of coarse agglomerates con
sisting of particles strongly sintered to each other. It has been
proposed that agglomeration is due to heat liberated during
grinding. Therefore, as indicated in , the duration of grind
ing should severely limited and determined by experiment
for each specific case. According to the authors of the pres-
ent articles, grinding duration for starting powders is5–6h.
It is also noted  that grinding of starting powder pro-
motes crystallization of mullite and tegtragonal ZrO
ramic material. After a short period of grinding (4–6h)
rapid mullite formation during firing is observed at
1180 – 1280°C; further mullite formation occurs over the ex-
tent of the next 350°C.
It has been established  that with an average content
of particles with a size of 0.5 mm in the starting powder the
increase in ultimate strength in compression and even elas
ticity modulus was about 30% compared with a specimen
containing particles with a size of more than 5 mm. It has
been noted that the size of mullite crystal particle that form,
which are 50 – 70 nm, and sometimes 80 – 95 nm, is of con
The aim of this work includes determining the effect of
ceramic powder fineness, including with addition of illite
clay, on formation and development of high-temperature
crystalline phases (mullite and ZrO
), and the mechanical
properties of mullite-zirconia ceramic.
The starting powder was prepared from a mixture con
sisting of synthetic materials, i.e., g-Al
at 550°C, amorphous SiO
. A mineral raw material was used in one part of the
Refractories and Industrial Ceramics Vol. 52, No. 1, May, 2011
1083-4877/11/05201-0035 © 2011 Springer Science+Business Media, Inc.
Riga Technical University, Institute of Silicate Materials, Riga,