PROPERTIES OF A MULLITE-ZIRCONIUM CERAMIC
SINTERED BY THE TRADITIONAL METHOD FROM POWDERS
OBTAINED DURING COMBUSTION
A. V. Hmelov
Translated from Novye Ogneupory, No. 2, pp. 29 – 38, February, 2015.
Original article submitted December 10, 2014.
Results are presented from a study of the growth of the crystalline phases, the size distribution of the pores,
and the size distribution of the particles that make up the powders. The powders were obtained by a wa
ter-based combustion method with the use of a mix containing solutions of nitrates of metals, SiO
an oxidant, and different fuels. The article reports results obtained from the formation of the crystalline phases
and data on the pore-size distribution, apparent density, degree of sintering, and physico-mechanical proper
ties of specimens sintered from the powders by the conventional method in the range 1300 – 1500°C with and
without the use of a clay addition. The powders formed by the combustion of carbamide and limonic acid are
characterized by developed mullitization and crystallization of the tetragonal phase of ZrO
, the formation of
coarse and relatively coarse pores, and the formation of fine and moderate-sized particles. The specimens
sintered from such powders in the range 1300 – 1500°C with a clay addition are characterized by developed
crystallization of the phases and maximum values for apparent density, degree of sintering, and the indices of
the physico-mechanical properties. These results stand in contrast to the results obtained for the specimens
sintered from similar powders without clay and specimens sintered from clay and powders obtained by the
combustion of glucose and saccharose.
Keywords: combustion process, mullite-zirconia powders, clay addition, conventional sintering, ceramic,
Producing finely dispersed initial powders with a narrow
particle-size distribution and a developed surface area is cur
rently the key to improving the phase composition, apparent
density, degree of sintering, and physico-mechanical proper
ties of mullite-zirconia ceramics [1, 2]. Powders of this type
can be obtained by infiltration [2, 3] and by modern (non-tra
ditional) methods of synthesis such as sol-gel synthesis ,
hydrothermal synthesis, and combustion [6 – 8].
The properties of the powders obtained by these methods
are controlled by controlling the conditions which exist dur
ing the synthesis process [4 – 8].
In all of the above-mentioned chemical methods of pro
ducing mullite and mullite-zirconia powders, during com
bustion the phases that are formed in the powder crystallize,
the product’s density decreases (pores are formed in it), and
the powders begin to disintegrate [6 – 8].
Powders with the properties described above can be ob
tained by regulating the proportions of metal nitrate (oxi
dant) and fuel [6, 7] and by using a strongly exothermic fuel
[7, 9], an active external oxidant [10 – 12], and excess fuel
As a result, the mullite and mullite-zirconia powders that
are obtained are characterized by rapid crystallization of the
mullite phase and the tetragonal phase of ZrO
, the formation
of moderate-sized and coarse pores (up to 85 mm), and the
presence of fine (10 – 35 mm) particles [6, 8, 12]. Agglomer
ates consisting of sintered particles are also formed in the
mullite-zirconia powder [7, 9, 12].
The formation of dense ceramic specimens during
sintering from powders obtained by the combustion method
is related to the diffusion of substances into the pores that
were formed during the decrease in the powder’s density, the
filling of the pores with these substances, and the reactivity
of the particles formed as the powder disintegrates [6, 7, 12].
Refractories and Industrial Ceramics Vol. 56, No. 1, May, 2015
1083-4877/15/05601-0072 © 2015 Springer Science+Business Media New York
Riga Technical University, Riga, Latvia.