312
V. Malyshev et al.
19.2 Materials and Methods
To investigate the conditions under which tungsten carbide is synthesized, electrolyte having the following composition was selected, expressed in terms of mole
percent, Na 2 WO 4 , 36.8; Li 2 WO 4 , 43.2; and Li 2 CO 3 , 20.0, or scaled on the basis of
elements and oxides and expressed in terms of weight percent, Na, 7.18; Li, 3.72;
WO 3 , 78.21; and CO 2 , 3.73. Sodium tungstate and lithium tungstate and lithium
carbonate are carefully dried at T = 200–250 ◦ C for 3–4 h and mixed in an agate
mortar. The prepared electrolyte is held in a platinum beaker at temperatures of 500,
800, and 900 ◦ C until it attains a constant mass. At specified intervals of time, the
beaker is removed from the furnace, cooled in a desiccator, and weighed. Once a
constant mass is achieved, the melt is cooled and weighed and a sample selected for
analysis in order to establish the content of Li, Na, WO 3 , and CO 2 .
Determination of the thermal stability of lithium carbonate and the dynamic
course of variation of the concentration of lithium carbonate in the course of
electrolysis is performed by means of chemical and thermogravimetric methods on
the basis of the content of carbon dioxide in the electrolyte [3, 4]. The chemical
method presupposes gasometric determination of the volume of CO 2 released in
the decomposition of a suspension of electrolyte by means of hydrochloric acid;
the concentration of carbon dioxide is calculated in light of the dependence of the
volume of the gas on temperature and atmospheric pressure.
The content of tungsten in the electrolyte is determined by the chemical method
of acidic hydrolysis [5]; tungsten oxide formed as a result of decomposition by
means of a mixture of HNO 3 -HF (4:1) is subjected to calcination prior to analysis
at a temperature of 750 ◦ C.
The content of Li and Na in the melt is estimated by means of atomic absorption
spectroscopy [6] on a Pye-Unicam instrument; the percentage content of the
elements was estimated from the intensity of waves of specific length from the given
element upon combustion of the investigated solution in the flame of an air-acetylene
or ethylene-oxide burner.
19.3 Results and Discussion
19.3.1 Variation of Composition of Electrolyte in Isothermal
Heating
At a temperature of 800 ◦ C and higher, lithium carbonate simultaneously evaporates
(in the form of Li 2 CO 3 ) and decomposes with the release of CO 2 until some
steady state is attained. The latter steady state is established after 2–3 h under
heating conditions at T = 800–900 ◦ C and after 30–35 h at T = 500 ◦ C (see Fig.
19.1). The maximum loss of the mass of electrolyte in the course of calcination
is at most 4.5% (by weight). It is evident from the data of chemical and atomic
V. Malyshev et al.
19.2 Materials and Methods
To investigate the conditions under which tungsten carbide is synthesized, electrolyte having the following composition was selected, expressed in terms of mole
percent, Na 2 WO 4 , 36.8; Li 2 WO 4 , 43.2; and Li 2 CO 3 , 20.0, or scaled on the basis of
elements and oxides and expressed in terms of weight percent, Na, 7.18; Li, 3.72;
WO 3 , 78.21; and CO 2 , 3.73. Sodium tungstate and lithium tungstate and lithium
carbonate are carefully dried at T = 200–250 ◦ C for 3–4 h and mixed in an agate
mortar. The prepared electrolyte is held in a platinum beaker at temperatures of 500,
800, and 900 ◦ C until it attains a constant mass. At specified intervals of time, the
beaker is removed from the furnace, cooled in a desiccator, and weighed. Once a
constant mass is achieved, the melt is cooled and weighed and a sample selected for
analysis in order to establish the content of Li, Na, WO 3 , and CO 2 .
Determination of the thermal stability of lithium carbonate and the dynamic
course of variation of the concentration of lithium carbonate in the course of
electrolysis is performed by means of chemical and thermogravimetric methods on
the basis of the content of carbon dioxide in the electrolyte [3, 4]. The chemical
method presupposes gasometric determination of the volume of CO 2 released in
the decomposition of a suspension of electrolyte by means of hydrochloric acid;
the concentration of carbon dioxide is calculated in light of the dependence of the
volume of the gas on temperature and atmospheric pressure.
The content of tungsten in the electrolyte is determined by the chemical method
of acidic hydrolysis [5]; tungsten oxide formed as a result of decomposition by
means of a mixture of HNO 3 -HF (4:1) is subjected to calcination prior to analysis
at a temperature of 750 ◦ C.
The content of Li and Na in the melt is estimated by means of atomic absorption
spectroscopy [6] on a Pye-Unicam instrument; the percentage content of the
elements was estimated from the intensity of waves of specific length from the given
element upon combustion of the investigated solution in the flame of an air-acetylene
or ethylene-oxide burner.
19.3 Results and Discussion
19.3.1 Variation of Composition of Electrolyte in Isothermal
Heating
At a temperature of 800 ◦ C and higher, lithium carbonate simultaneously evaporates
(in the form of Li 2 CO 3 ) and decomposes with the release of CO 2 until some
steady state is attained. The latter steady state is established after 2–3 h under
heating conditions at T = 800–900 ◦ C and after 30–35 h at T = 500 ◦ C (see Fig.
19.1). The maximum loss of the mass of electrolyte in the course of calcination
is at most 4.5% (by weight). It is evident from the data of chemical and atomic