STRENGTHENED POROUS CERAMIC
BASED ON MULLITE AND CORUNDUM
E. S. Lukin,
F. A. Akopov,
G. P. Chernyshov,
and T. I. Borodina
Translated from Novye Ogneupory, No. 7, pp. 38 – 39, July 2008.
Original article submitted January 15, 2008.
Data are provided for manufacturing technology and ceramic properties of porous ceramics of mullite-
corundum composition. The ultimate strength in compression of this ceramic is several times higher than
commercial porous aluminosilicate ceramics.
Development of porous ceramic materials with an
inhomogeneous granular structure exhibiting high strength is
important for contemporary technology. These materials may
be used successfully in systems for protection against
dynamic action, and as a refractory structural material in
furnace units under static loading conditions. An inhomo-
geneous structure leads to rapid damping of stresses that
arise on loading. If a strong bond is obtained between grains,
then there is an increase in crack resistance ceramic strength.
Work has been carried out in this direction recently. For
example, results are provided in  for studying the
possibility of creating high-strength porous material based
on the system Al
by synthesis, and then breakdown
of the chemical compound Al
during heat treatment.
Very fine (nanosize) aluminum and titanium oxides released
during its breakdown form as a result of sintering at
1200 – 1300°C a high-strength ceramic bond that makes it
possible with open porosity of 20% to have an ultimate
strength in compression reaching ~500 MPa. However, this
method for creating a ceramic is not free from disadvantages,
the main ones of which are:
a multistage process for preparing objects, i.e. additional
ceramic heat treatment is required after firing;
the narrow temperature limits for performing synthesis
decomposition requires careful observation of
firing and heat treatment regimes.
The aim of this research is to study the possibility of
preparing porous high-strength ceramic in the corundum –
mullite system. Mullite was initially synthesized for the
purpose. The starting materials for synthesizing mullite and
ceramic preparation were alumina grade GLMK and analy
tical grade silicon dioxide.
In order to synthesize mullite a mixture containing 62%
and 38% SiO
was prepared, and from it briquettes
were formed and fired at 1600°C for 5 h. The completeness
of synthesis was monitored by x-ray phase analysis (XPA).
As analysis showed, the amount of mullite in fired material
exceeded 72% (Table 1). In view of the significant content in
fired briquettes of silica in the form of a-cristobalite (~24%)
it was called by us a “high-alumina (HA) compound.”
The main composition selected was 60 wt.% corundum
— 40 wt.% HA. Alumina was used in the form of ground
fine powder with a particle size of 2 – 4 mm. The HA
compound was used in the form of coarse-ground material
with a particle size of 50 – 100 mm. An additional streng
thening addition to the compound charge was 2% (above
100%) finely-dispersed mixture containing 65% SiC and
35% MgO . The mixed powder particle size was ~2 mm.
During firing the silicon carbide oxidized to silica. The highly
active silica formed reacted with MgO and Al
went into forming clinoenstatite MgSiO
little more than 20% into forming an additional amount of
mullite (secondary compound). Clinoenstatite reacted by
diffusion with coarse grains of mullite and with corundum.
Refractories and Industrial Ceramics Vol. 49, No. 4, 2008
1083-4877/08/4904-0298 © 2008 Springer Science+Business Media, Inc.
D. I. Mendeleev Russian Chemical Engineering University
TABLE 1. Results of X-Ray Phase Analysis of a Briquette and
Specimen Main phases Small amount of phases
Briquette Mullite (> 72%),