88 Notizen
Excess Free Energies in Molten
CuCl-KCl-LiCl by EMF Measurements
Z. Giazitzoglou, H. Engels, and U. Schiller Lehrstuhl f ü r Technische T h e r m o d y n a m i k an der R W T H Aachen
Z. N a t u r f o r s c h . 38 a, 8 8 - 8 9 (1983);
received O c t o b e r 9, 1982
T h e ternary liquid system CuCl-KCl-LiCl has been investigated by means of emf measurements at a b o u t 450 u p to 700 °C. Excess free energies and activity coefficients for molten C u C l in the KCl-LiCl eutectic are calculated by a best fit to the obtained data and f r o m literature data for the corresponding binary systems employing the Redlich- Kister equation.
I n t r o d u c t i o n
In contrast to the investigations presented in [1], emf measurements for a very pure C u C l quality (Ventron Karlsruhe, F R G , No. 400151, 99.999%) in molten KCl-LiCl eutectic (41.5 mol% KCl) have been carried out in the present work using a revers- ible CuCl formation cell and a technique which has been described previously [I, 2], Excess free energies for the ternary system, using data for the three cor- responding binary systems, have been calculated by a method already reported [2]. The following indi- cation has been chosen here for the components:
CuCl = 1, KCl = 2, LiCl = 3.
R e s u l t s
The emf measurements, corrected according to the relations given in [1], are plotted in Fig. 1 versus t e m p e r a t u r e for various concentrations of CuCl.
Their least squares lines are presented in form of the following equations:
X\ = 0.0202 ( £ - £ ° ) / m V = - 10.7 + 0.4203 T 0.0795 - 14.8 + 0.2990 T 0.1010 - 6.2 + 0 . 2 6 8 2 T 0.1407 1 . 1 + 0.2247 T 0.1761 - 13.7 + 0.2211 T 0.2451 - 4.9 + 0 . 1 7 1 3 T
where a'I : mole fraction of CuCl, E: measured emf, E°: standard emf of pure liquid CuCl, T / K .
Reprint requests to Z. Giazitzoglou, Lehrstuhl f ü r Tech- nische T h e r m o d y n a m i k an der R W T H Aachen, D-5100 Aachen.
T h e partial molar excess free energy of CuCl (Gf) in the system investigated has been calculated from the present data using the Margules equation
= (i - a ,)2 [A + 2{B - A) .y,]. The coefficients ob- tained are A/J m o l '1 = 1144 - 8.488 T and B/J m o r1 = 653 - 9.197 T with T / K .
In order to d e t e r m i n e the integral molar excess free energy of the ternary system CuCl-KCl-LiCl the integral excess free energies for the correspond- ing binary systems have to be calculated applying the Redlich-Kister equation. By using the emf mea- surements for the CuCl-KCl system [3] and for the C u C l - L i C l system [4] the following results have been achieved:
C u C l - K C l Gf2 = .y, .y2 [An + Bn (.y, - .y2)],
A,2 = - 6054 - 30.155 T, Bv = 5554 - 12.402 T;
CuCl-LiCl Gf3 = * , A3 [A|3 + 5, 3 (.y, - .y3)],
A, 3 = 13471 - 15.221 T,
B, 3 = 1138 - 3.444 T.
F o r the KCl-LiCl system holds [2]: 623 = ^23*2*3,
^23 = - 17991 + 5.753 T, where Gp/J m o l- 1, T / K . T h u s the integral excess free energy of the CuCl- KCl-LiCl system (GE), the partial excess free energy of CuCl (GE) according to the following equation
Gf = A,2*2 (1 - * , ) + A13.y3 ( 1 - x , ) - ^23 * 2 * 3
+ 2(B12XIX2 + £13*1*3) " (Bnx\+ Bnx])
~ 2 [ ß i 2 * I * 2 ( * l ~ * 2 ) + # 1 3 * l * 3 ( * | - * 3 ) ] 1400.
1300.
1200.
1100.
400. 500. G00.
t/°c
700.
Fig. 1. Plots of emf m e a s u r e m e n t s vs. t e m p e r a t u r e at the concentrations investigated.
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N o t i z e n 89
1.0 Fig. 2. Plots of t h e integral (GE) and partial m o l a r (<7^)
excess free energies and activity coefficient (y,) of C u C l calculated f r o m b i n a r y d a t a at three t e m p e r a t u r e s ( ), a n d the e x p e r i m e n t a l (.v) and t h e r e b y calculated ( ) d a t a at 600 ° C in the molten C u C l - K C l - L i C l system.
and its activity coefficient (y,) are obtained, being presented in Fig. 2 for three temperatures. T h e r e result some deviations f r o m the experimental data, as exemplified by the curves shown for 600 °C.
. 0
- 2 . 0
T - 4 . 0 G
- 6 . 0
—> - 6 . 0
W O - 8 . 0
• 1 0 . 0
• 1 2 . 0
600 °C
i o c i / i o o / foo
8 1 - 0
D i s c u s s i o n
T h e present emf results lie on the average by a b o u t 5 mV higher than the values achieved in [1]
with a less p u r e CuCl quality. T h e r e f o r e s o m e w h a t higher values result in this work for the excess properties of CuCl.
T h e m e t h o d for calculating the t h e r m o d y n a m i c excess properties of a ternary system f r o m binary data was successfully used in [2,5] for similar molten chloride mixtures. T h e p r o b a b l e reason for the deviations a p p e a r i n g here is the different source of the data used. This is also confirmed by the fact that the literature d a t a for the CuCl-KCl and CuCl-LiCl systems [3, 4] used in this work are not in agreement at all with the results published in [6]
by the s a m e authors a b o u t these mixtures. Especial- ly in the case of the C u C l - L i C l system there appears a sign reversal for the excess free energies [4] not typical for this kind of salts. Because of the uncer- tainty arising in regard to the quality of the avail- able binary d a t a no ternary interaction terms for the investigated system by correlation of the experi- mental data o b t a i n e d in this work were determined.
This work was s u p p o r t e d by the G e r m a n Re- search P a r t n e r s h i p (Project SFB 163).
[1] Z. G i a z i t z o g l o u , Electrochim. Acta, accepted for publi- cation.
[2] Z. Giazitzoglou, Ber. Bunsenges. Phys. C h e m . 86, 894 (1982).
[3] P. M i r a b e l and J. G u i o n , C. R. Acad. Sei. Paris, Ser.
C 2 6 9, 5 1 6 (1969).
[4] P. D a n t z e r a n d P. M i r a b e l , C. R. Acad. Sei. Paris, Ser.
C 271,901 (1970).
[5] B. F. M a r k o v , Rev. R o u m . C h i m . 1 7, 2 0 3 (1972).
[6] J. Brenet, P. D a n t z e r , P. M i r a b e l , and J. G u i o n , Rev.
R o u m . C h i m . 1 7, 5 7 (1972).
