Thermodynamics of CaO–Al2O3–SiO2 and CaF2–CaO–Al2O3 –SiO2 melts
Abstract
Exchange reactions, occurring in
CaF
2
–CaO–Al
2
O
3
–SiO
2
liquid solution, and reactions
between
CaF
2
–CaO–Al
2
O
3
–SiO
2
, or
CaO–Al
2
O
3
–SiO
2
melts and Ta, Nb or Mo have been studied, using Knudsen
effusion mass spectrometry. SiF
3
+
,
SiF
2
+
, SiF
+
,
CaF
2
+
, CaF
+
,
Ca
+
, Al
2
F
5
+
,
AlF
3
+
, AlF
2
+
,
AlF
+
, Al
+
, AlOF
+
,
SiO
+
, MO
+
, MO
2
+
(M=Nb, Ta, Mo) and MoO
3
+
were detected
in the mass spectra of the saturated vapour.
SiF
4
, AlF
3
, AlOF, SiO, CaF
2
and MO
2
were found to be the main vapour species
and their partial vapour pressures were measured and used
for calculation of the components' activities. The
activities, computed in different ways, were in good
agreement. Representative files of experimental data
comprising ca. 3500 activities of all components in
the
CaF
2
–CaO–Al
2
O
3
–SiO
2
liquid solution and more than
350 values of a(SiO
2
) in the
CaO–Al
2
O
3
–SiO
2
melt at various temperatures and concentrations were
obtained. The thermodynamic functions of the liquid
solutions were described by the associated-solution model
under the assumption that binary and ternary associates and
SiO
2
polymer complexes exist in the melts. The
model and the thermodynamic functions of solid compounds
were applied for the computation of phase equilibria in the
CaO–Al
2
O
3
–SiO
2
and
CaF
2
–CaO–Al
2
O
3
–SiO
2
systems. The computed
coordinates of the ternary invariant points are shown to
agree with the available experimental data.
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