1070-4272/01/7405-0890$25.00C2001 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 74, No. 5, 2001, pp. 890 !891. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 5,
2001, pp. 863!864.
Original Russian Text Copyright + 2001 by Bokovikova, Dvadnenko.
Synthesis of Garnets by Coprecipitation from Aqueous Solutions
T. N. Bokovikova and M. V. Dvadnenko
Kuban State Technical University, Krasnodar, Russia
Received July 13, 2000; in final form, March 2001
Abstract-Conditions for the coprecipitation of hydroxides of aluminum and rare-earth elements from
O system (Ln = La, Sm) by NH
O solutions at 25oC were studied.
The resulting precipitates were investigated by thermal analysis, IR spectroscopy, and X-ray phase analysis.
A wide application of aluminum garnets of rare-
earth elements (REE) to quantum electronics promoted
the synthesis and study of garnet-structure com-
pounds. Yttrium aluminum garnet, which is one of
the best solid-state laser materials, has been the most
The garnet-structure compounds can be obtained by
solid-phase synthesis from a mixture of oxides and
also by coprecipitation of hydroxides from salt solu-
tions. One of the shortcomings of the solid-phase
synthesis is high temperature (higher than 1600oC).
The coprecipitation technique makes it possible to
obtain compounds with required structures as well
crystallized and finely dispersed products even at
100031200oC. The data on this technique are con-
tradictory and few in number , thus its application
to the synthesis of REE aluminum garnets requires its
further more extended study.
The aim of this work was to study the dehydration
and interaction of hydroxides of aluminum and lan-
thanides, coprecipitated from aqueous solutions of
their salts by an ammonia aqueous solution, and to
demonstrate a possibility of obtaining lanthanum and
samarium garnets by calcination of coprecipitated
hydroxides at 96531050oC. The experimental methods
in use were differential thermal analysis (DTA), IR
spectroscopy, and X-ray analysis.
The hydroxides were precipitated from the
O system by a 4%
solution of NH
O with permanent stirring of
the suspension. The concentrations of aluminum and
rare-earth nitrates were kept constant (1.66 and 1.00 N,
respectively), and pH was maintained at 9.5310. The
thermal analysis of precipitates was carried out on
a D derivatograph at a heating rate of 10 deg min
The IR spectra were recorded on a Specord 75-IR
spectrometer in the range 40034000 cm
temperature from Nujol mulls. Phase compositions
was analyzed on a DRON-1 diffractometer (FeK
As the NH
O content in the starting mixtures
increased, the following reaction stages occurred
sequentially: the formation of poorly filterable col-
loidal precipitates, quantitative precipitation of alu-
minum and REE hydroxides with an impurity of basic
salts, and, finally, the coprecipitation of aluminum
and REE hydroxides. The resulting precipitates were
washed with distilled water until nitrate ions dis-
appeared and dried at 25oC for 12 h .
A number of endo- and exothermic effects were
observed upon heating (Fig. 1). The endothermic ef-
Fig. 1. DTA curves of coprecipitated aluminum and
REE hydroxides. (T) Temperature. (1) La(OH)