ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2006, Vol. 51, No. 4, pp. 531–532. © Pleiades Publishing, Inc., 2006.
Original Russian Text © G.K. Shurdumov, Z.V. Shurdumova, Z.A. Cherkesov, A.M. Karmokov, 2006, published in Zhurnal Neorganicheskoi Khimii, 2006, Vol. 51, No. 4,
pp. 583−584.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
Synthesis of Alkaline-Earth Metal Tungstates in Melts
of [NaNO –M(NO ) ] –Na WO (M = Ca, Sr, Ba) Systems
3
3 2 eut
2
4
G. K. Shurdumov, Z. V. Shurdumova, Z. A. Cherkesov, and A. M. Karmokov
Kabardino-Balkar State University, ul. Chernyshevskogo 173, Nalchik, 360004 Russia
Received September 10, 2005
Abstract—Alkaline-earth metal tungstates are synthesized in NaNO –M(NO ) (M = Ca, Sr, Ba) eutectic
3
3 2
melts. The synthesis is based on the exchange reaction of calcium, strontium, or barium nitrate with sodium
tungstate.
DOI: 10.1134/S0036023606040036
Calcium, strontium, and barium tungstates have sev-
Here calcium, strontium, and barium tungstates
eral valuable properties and are promising materials for were synthesized by exchange reactions in melts of
new technologies [1–7]. Their applications include [NaNO –M(NO ) ] –Na WO (M = Ca, Sr, Ba) sys-
3
3 2 eut
2
4
matrix laser materials, γ-radiation detectors, ceramics tems. The values of the Gibbs free energies for these
strontium tungstate), luminophores (calcium, stron- compounds (Table 1), which were calculated by the
(
tium, and barium tungstates), radioelectronics (calcium Temkin–Shvartsman method [9], show that the reac-
and barium tungstates), and other fields. Therefore, the tions are directed toward the coupling of alkaline-earth
development of rational methods for the synthesis of metal cations and the tungsten ion. In addition, these
these compounds is of scientific and applied interest. reactions are fast, as all reactions in ionic melts. The
The presently known methods for the preparation of temperature schedule of the synthesis was chosen and
alkaline-metal tungstates [1, 3, 5] are based on either the compositions of the starting mixtures of the reac-
their precipitation from aqueous solutions or solid- tants were calculated from the thermal analysis data for
phase reactions of tungsten(VI) oxide with calcium, the sodium nitrate–calcium (strontium, barium) nitrate
strontium, and barium carbonates or nitrates.
systems [10, 11] using the stoichiometric equation
The compositions of the precipitates formed in
aqueous solutions depend on the concentration of the
reactants, the pH of solutions of the starting tungstates,
the phase contact time, and other factors. In addition,
since the tungstate precipitates are highly disperse, they
are poorly filterable. The solid-phase reactions take a
long time, occur at high temperatures, and do not
always yield a highly pure compound. At present, syn-
thesis in molten salts is an attractive route to obtaining
several valuable compounds [8]. Among such salts,
alkali-metal nitrates play a special role, in our opinion;
their physicochemical properties (low melting temper-
atures, simple structures in the liquid state, relatively
xNaNO + yM(NO ) + yNa WO
3
3 2
2
4
=
yMWO + (x + 2y)NaNO ,
4 3
where x and y are the numbers of moles of the salt sol-
vent and reactants, respectively. The calculated data are
listed in Table 2.
Recrystallized and dehydrated sodium, calcium,
strontium, and barium nitrates, and sodium tungstate
analytical or reagent grades) were used as the starting
compounds.
Experiments were carried out in wide fused quartz
(
high thermal stability, and high solubility in water) tubes at 400°C with periodic stirring of the melt. After
make them promising reaction vessels and reactants. 40–50 min of the reaction, the melt was poured into a
Table 1. Gibbs energies for the exchange reactions of calcium, strontium, and barium nitrates with sodium tungstate in melts
of the NaNO –M(NO ) (M = Ca, Sr, Ba) systems
3
3 2
∆
G (kJ/mol) of reaction in systems
T, K
Na WO –Ca(NO )
Na WO –Sr(NO )
Na WO –Ba(NO )
2
4
3 2
2
4
3 2
2
4
3 2
2
73
73
73
–98.87
–101.57
–102.65
–51.47
–58.92
–61.90
–99.39
–95.89
–94.49
7
9
5
31