SYNTHESIS OF LOW-MELTING EUTECTIC
OF THE CaO–B
SYSTEM IN A SOLID PHASE
M. A. Vartanyan,
N. A. Popova,
and E. S. Lukin
Translated from Novye Ogneupory, No. 7, pp. 43 – 46, July 2011.
Original article submitted May 3, 2011.
Results are provided for a physicochemical study of processes that occur during synthesis of eutectic composi
tion of the CaO–B
system in a solid phase, and the possibility of their activation by using starting
calcium-containing components with different chemical and thermal prehistory. It is established that inde
pendent of the form of starting components, in all cases there is formation of a crystalline eutectic phase, and
the sequence of physicochemical processes that occur is determined by the reaction capacity of the calcium
Keywords: eutectic synthesis in solid phase, calcium oxide, microstructure, phase formation.
A distinguishing feature of material of eutectic composi-
tion is an entirely crystalline structure, whose phase compo-
nents are distributed consistently , and this provides high
property uniformity throughout a material volume. The most
extensive use of eutectics is in metallurgy, and also sin-
gle-crystal technology since the simplest method for forming
this structure is solidification from a melt. In ceramic (pow-
der) technology eutectics are used exclusively as additions,
reducing the sintering temperature of the main component
due to liquid phase formation with subsequent crystallization
during cooling. It should be noted that studies devoted to cre
ating materials of eutectic composition for ceramic technol
ogy are limited [2, 3].
The aim of this work is to study the physicochemical
processes that occur during synthesis of eutectic composition
into a solid phase, and methods for activating sub-solidus
material synthesis of eutectic composition from starting
components with different chemical and thermal prehistory.
The object for study was a composition of the CaO–B
system, relating to a readily melting eutectic with a
melting temperature of 977°C. Calcium oxide within the
composition of the reaction mixture was introduced through
calcium-containing components of different nature: industri
ally produced calcium salt, i.e., carbonate, chloride (6-hy
drous), and nitrate (6-hydrous), and also calcium oxide pre
pared by decomposition of these salts. An estimate was also
made of the effect of conditions for preparing calcium oxide
from compounds on its reaction capacity. Boron oxide within
the composition of the mixture was added in the form of bo-
ric acid, and silicon dioxide was added in the for form of
very fine amorphous silica, (silica filler).
Heat treatment regimes for starting mixtures for synthe-
sizing eutectic composition phases were selected from re-
sults of their differential thermogravimetric (DTA, Fig. 1)
and dynamic x-ray phase (DXPA)
analyses. An estimate of
the occurrence of synthesis was carried from the results of
DXPA, shown in Fig. 2; the microstructure of heat treatment
products was also studied (Fig. 3).
Material prepared by heat treatment of composites based
on calcium carbonate was made up from three crystalline
phases, i.e., CaO·B
, and CaO·SiO
. All of the com
ponents were uniformly distributed throughout the material
volume, and particles had a size from 2 to 4 mm (see
Fig. 3a ). On the DXPA curve for this composition (see
Fig. 2a ) peaks of all of the material components of the crys
talline phases appeared at 500 – 600°C, and their final for
mation occurred in the range 750 – 800°C.
Material based on calcium nitrate was made up of crys
talline phases of calcium metaborate and silicate, and also
silicon dioxide. The size of primary crystals was 6 – 10 mm
(see Fig. 3b ), on the DXPA curve (see Fig. 2b ) peaks for all
of the crystalline phases appeared at 800°C, which were pre
Refractories and Industrial Ceramics Vol. 52, No. 4, November, 2011
1083-4877/11/05204-0278 © 2011 Springer Science+Business Media, Inc.
FGBOUVPO D. I. Mendeleev Russian Chemical Technology
University, Moscow, Russia.
The authors of the article thank senior scientific worker of
ISMAN D. Yu. Kovalev for help in performing the studies.