Handbook of Solvents - George Wypych - ChemTech - Ventech!

1490 Victor Cherginets
Thermal dependence of ZrO 2 solubility (molar fraction, N) in molten KCl-NaCl was
evaluated in the temperature range of 973-1174 K: 39 N=(-5.7±3.1)×10-6 + (7±3)×10 -9 ×T.
ZrO 2 solubility at t~700 o C was negligible.
Barbin et al. 40,41 determined thermal dependence of Li 2O solubility in equimolar mixture
KCl-NaCl by isothermal saturation technique in temperature range of 973-1073 K:
N=0.107-5.221/T, in this range the solubility varied from 0.52 to 0.86 mol%. In earlier work
by Kaneko and Kojima, 42 the solubility at 973 K was lower (0.31 mol%). The solubility of
lithium oxide was close to that for BaO.
Solubility products of some oxides in molten KCl-NaCl in molarity scale are presented
in Table 21.3.1 and plotted in Figure 21.3.1 (data obtained by same authors are connected
by lines).
Table 21.3.1. Oxide solubilities in molten KCl-NaCl at 700 o C (-log P, molarities)
Oxide pP 11,28-32
pP 29
pP 8
pP 9
pP 33,38
MgO 9.00±0.15 8.46 9.27±0.06
CaO ~6.29 6.62 8.36 4.36±0.06
SrO 3.00 5.84 7.60 3.08±0.40
BaO 2.31±0.05 4.22 7.05 2.30±0.15
NiO 11.2 8.32 9.03±0.06
ZnO 6.18 6.93±0.20
Cu2O 5.4 4.17±0.30
MnO 6.78±0.05
CoO 7.89±0.03
CdO 5.00±0.03
PbO 5.12±0.05
Two groups of values are presented: obtained from isothermal saturation and
potentiometric results. The precision of results from isothermal saturation is worse. The
potentiometric results should give lower values than isothermal saturation because it includes
molecular oxide concentration. Figure 21.3.1 shows that results have opposite trend
to [21.3.10].
The following explanation of the above discrepancy is proposed. 43,44 Let us consider
the chemical potential, μ, of oxide in its saturated solution:
0
μ = μ + RT lns
MeO, s MeO, l MeO, l
[21.3.14]
From this equation it follows that the oxide solubility should be constant. But every
precipitate possesses a definite surface, hence, the effect of latter should be taken into account,
too:
where:
0
μ + σS = μ + RTlns MeO, s MeO, l MeO, l
σ the surface energy
S molar surface square of the precipitate
[21.3.15]