ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 11, pp. 1885–1889. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © O.G. Gromov, A.P. Kuz’min, G.B. Kunshina, R.M. Usmanov, E.P. Lokshin, 2008, published in Zhurnal Prikladnoi Khimii, 2008,
Vol. 81, No. 11, pp. 1767–1771.
Microwave Synthesis of Barium Titanate, Strontium Zirconate,
and Sodium Indium Tungstate
O. G. Gromov, A. P. Kuz’min, G. B. Kunshina, R. M. Usmanov, and E. P. Lokshin
Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials, Kola Scientific Center,
Russian Academy of Sciences, Apatity, Murmansk oblast, Russia
Received March 6, 2007
Abstract—The results of microwave (at a frequency of 2.45 GHz) synthesis of BaTiO
are compared with those of the common solid-phase synthesis.
Single-phase finely dispersed (desirably nanocrys-
talline) powders of barium metatitanate and strontium
metazirconate are required for the production of multi-
layer ceramic capacitors.
Previously  we examined the solid-phase synthe-
sis of powdered barium titanate with titanium oxide
and oxyhydroxide and barium carbonate, nitrate, and
hydroxide as starting compounds. Because the inten-
sity of the solid-phase synthesis and the quality of the
final product largely depend on the perfection of the
mixture of the starting powders, this mixture was sub-
jected to ultrasonic mechanical activation in an inert
organic liquid. We found that single-phase BaTiO
containing no Ba
formed from a mixture of titanium oxyhydroxide and
barium nitrate upon treatment at 650°C for 2 h.
The drawback of this process is high content of the
residual organic liquid in the filtered and dried mixture
of the starting components. Calcination of such a mix-
ture is accompanied by formation of pyrolytic carbon,
and, to ensure its complete burn-out, it is necessary to
increase the calcination temperature to 700–750°C,
which leads to coarsening of the final product particles.
The specific surface area of the samples obtained did not
exceed 0.5 m
. To obtain single-phase NaIn(WO
by common solid-phase synthesis, a mixture of the
starting compounds (WO
) is pellet-
ized and calcined at 950°C for 50 h . It follows from
the aforesaid that, to prepare these substances, it is
necessary to accelerate solid-phase processes so as to
decrease the calcination temperature and/or time.
Microwave heating is widely used today for accel-
erating various processes, including sintering, dehydra-
tion, and decomposition of salts and hydroxides .
Microwave radiation is a nonionizing electromagnetic
radiation with a frequency from 0.3 to 30 GHz. As stip-
ulated by the international agreement, laboratory and
household microwave ovens use frequencies of 0.915
and 2.45 GHz. As shown in , the latter frequency is
preferable for the synthesis of ceramic materials.
In microwave solid-phase synthesis, the direct reac-
tion of powdered components occurs only if at least
one of them efficiently interacts with microwaves. If
the starting substances are poor microwave acceptors,
a secondary acceptor is added. This additive should be
chemically inert, should efficiently absorb microwave
radiation, and should be readily separable from the
synthesis products after the process completion.
The commonly used absorbing additive is high-
purity powdered graphite (particle size about 7 μm).
To perform the synthesis, a mixture of the starting
compounds is pelletized, pellets are placed in a quartz
test tube and covered with graphite powder, and the
mixture is irradiated in a microwave oven. Owing to
the high microwave susceptibility, graphite lights up
and heats pellets, initiating the decomposition of ni-
trates or carbonates. It was found that a hot oxide mix-
ture well interacts with microwaves, which provides
rapid reaction to obtain the required product .
AND INDUSTRIAL INORGANIC CHEMISTRY
In the course of microwave heating of a sample,
correct measurement of temperature is very difficult.