ntEASUREMENT OF
ACTIVITIES IN GALLIUM-INDIUM LIQUIDALLOYS
groups on the surface. The latter would be similar to those on HY and if in cage positions could react with pyridine to form pyridinium ions. Indications of the formation of these OH groups are given in spectra D, E, and F of Figure 2. Analogous effects occur on MgY. With the Na form and presumably the Li and K forms as well, the polarizing power of the ions is not sufficient to dissociate significant amounts of water to
1047
form structural OH groups. However, Basila, Kantner, and Rhee3 do report that water on a K-poisoned amorphous silica-alumina catalyst transforms a small portion of the Lewis into Brgnsted sites. Their studies were done at 150” rather than the 260” used in the present study. This low temperature could have caused the concentration of adsorbed species to be sufficiently high to detect their existence.
Measurement of Activities in Gallium-Indium Liquid Alloys’ lby G. J. Macur, R. K. Edwards, and P. G. Wahlbeck Department of Chemistry, Illinois Institute of Technology, Chicago, Illinois
60616
(Received September 65,1967)
Activities for both components have been determined for the Ga-In system. Activities were derived from effusion measurements utilizing the multiple Knudsen-cell effusion technique. Positive deviations from ideality occur for the activities of both components. Entropies of mixing were derived from the free-energy data of this study and calorimetric data recently reported in the literature. Integral entropies of mixing were found to be less than values for ideal solutions.
Introduction Thermodynamic information for binary liquid metal alloys is important to the advancement of theories of metals. I n the work being reported, thermodynamic activities in the Ga-In system have been determined experimentally. No direct experimental measurements have been reported in the literature. Activities were obtained from Knudsen effusion measurements leading to evaluations of partial pressures of the alloy components. The effusion measurements were performed by means of a “multiple Knudsen-cell” technique.2 Essentially, the technique consists of performing simultaneous measurements for a large number (up to 14) of alloy compositions, each of which is contained within its own effusion cell, and all cells are contained within the same isothermal zone (large molybdenum block). This technique was developed specifically to achieve for each selected temperature a high relative precision in that set of data. Thus, improved consistency should be achieved in evaluations making use of the Gibbs-Duhem integration method, since the integration appropriately is being performed for a set of data which are truly isothermal. This improvement is desirable, particularly if no direct measurement is made of the composition of the effusing vapor, but instead, compositions are obtained by the “calculation m e t h ~ d . ” ~Since both components are volatile in the Ga-In system, compo-
sitions of the gas phase must necessarily be evaluated. The calculation method was chosen because it greatly simplifies the experimentation, although it does demand data of high relative precision. Previous information bearing on the thermodynamic activities of the gallium-indium system is of an indirect nature. Svirbely and Read, utilizing information on the ternary Zn-In-Ga system, calculated activities for this binary system. Brossa and Bros, Castanet, and Laffitte5b have recently reported calorimetric measurements of enthalpies of mixing for the Ga-IA system.
Experimental Section Apparatus and Procedure. The total rates of effusion of gallium and indium from 14 alumina Knudsen cells under isothermal conditions were measured with an ap-
(1) Based on a thesis by G. J. Macur submitted to the Illinois Institute of Technology, Chicago, Ill., in partial fulfillment of the requirements for the Ph.D. degree, 1965. Presented before the Physical Chemistry Division a t the 150th National Meeting of the American Chemical Society, Atlantic City, N. J., Sept 1965. (2) G. J. Macur, R. K. Edwards, and P. G. Wahlbeck, J. Phys. Chem., 70, 2956 (1966). (3) R. K . Edwards and M. B. Brodsky, J . Am. Chem. Soc., 78, 2983 (1956). (4) W. J. Svirbely and 9. M. Read, J . Phys. Chem., 66, 658 (1962). (6) (a) J. P. Bros, Compt. Rend., 263, 977 (1966); (b) J. P. Bros, R. Castanet, and M. Laffitte, ibid., 264, 1804 (1967).
Volume 76, Number 3 March 1968
1048 paratus which has been previously described;2 all procedures used in obtaining the data were also described. Effective orifice areas were determined by allowing mercury to effuse through the orifice; the vapor pressure of mercury was calculated from an equation evaluated by Carlson, et U Z . , ~ based on the data of Busey and Giauque.’ The orifice areas were corrected for thermal expansion appropriate for the temperature of the run by using the linear coefficient of thermal expansion of 7.8 X deg-1.8 Materials. Indium wire and gallium metal with stated purities of 99.999% were purchased from A. D. Riackay, Inc. Indium wire was washed with pure benzene prior to insertion into the Knudsen cells. Since gallium metal reacts slowly with moist air, the amount of exposure to the laboratory atmosphere of the gallium was minimized. Alloy Compositions. Alloy solutions of desired compositions were prepared initially by adding appropriate masses of indium and gallium to the Knudsen cells. Each Knudsen cell contained at least 6 g of alloy. The composition of a given alloy was assumed to remain constant during an effusion run. In the worst case, the mole fraction of indium, XIn, changed by less than 2 ppt during the course of a run at a particular temperature. For 1.0 > XI, > 0.4, indium in the amount corresponding to the observed mass loss was added to the Knudsen cell at the end of each run. The addition of indium was an attempt to restore the composition of the alloy to its original value in preparation for a subsequent run at a new temperature and was based on the assumption that gallium volatilization was negligible. The validity of the latter assumption became obvious during the course of the final evaluations of activities.
Results The experimental data are presented in Table I. Activities of I n in the Ga-In liquid solutions were calculated using the definition for activity: ;I,, = pIn/pIno, where PI, is the partial pressure of I n in equilibrium with the alloy and pInois the vapor pressure of pure In. The p1,O values were obtained from earlier experiments2 in which the same apparatus was used. The activity coefficient, 71,) was computed by setting 71, = aIn/X1,, where XI, is the atom fraction of In in the liquid metallic solution. For computation purposes the a function of Darken and Gurry9 was used: ai = log ri/(l - Xi)2. For solutions containing less than 5% indium, the partial pressure of gallium must be less than that of pure Ga, and it was assumed initially to be greater than the partial pressure given by Raoult’s law. (Later the assumption was validated completely by the activity data.) Because of the very low concentrations of In, (YI, varies only slightly between these two indium The Journal of Physical Chemistry
G. J. MACUR,R. K. EDWARDS, AND P. G. WAHLBECK pressure limits. For example, with cell I at 1269”K, = 0.0399, a I n was 0.36 and 0.34, respectively, and the average value was taken. For solutions containing more than 5% indium, the calculation method of Edwards and Brodsky3 was used. The calculation method uses a successive approximation to obtain the true activities. A firstcalculated a, a1,(1), was determined from the Knudsen-cell data by assuming that the vapor in equilibrium with the Ga-In alloys was pure indium; this assumption is a good one since the vapor pressure of pure indium is ca. 11 times that of pure gallium.2 The , smoothing the data to a curve, values of a ~ , ( l ) after were used to calculate a first curve for aGa(l)loand aI,,(l). For a second approximation in the calculations for a~,,,the values of a G a ( l ) and a1,(1) were used to determine the vapor composition. Values of aIn(2) were used to calculate aG8(2) and a1,(2). Any further successive treatments produced changes in activities which were much smaller than the experimental uncertainties in the data, and hence values of a and a used in later calculations for solutions containing more than 57, indium are from the second approximation. A difficulty arose in run 3. It was found that the measuring thermocouple did not reach the same position in the molybdenum block as in the two previous runs. For this reason, the measured temperature was suspected to be incorrect, and this inference is supported by the observation of inconsistent a values for indium when the measured value for the temperature is used. The mass-loss rates calculable from the data in Table I indicate that the temperature of run 3 is between that of runs l and 2 . I n order to obtain a corrected value of the temperature for run 3, an interpolative procedure was devised. A “calculated” temperature for each cell, B through G, for run 3 was evaluated by interpolating from a linear log 71, US. 1/T plot between sets 1 and 2 for the given cell. Actually, since TI, is a function of temperature, the procedure involved the appropriate successive interpolations. The average of these calculated temperatures, 1247”K, was selected as the temperature of run 3 and wag only 4” higher than the measured temperature. The data from run 3 are, in comparison with those from the other
XI,
( 6 ) K. D. Carlson, P. W. Gilles, and R. J. Thorn, J. Chem. Phys., 38, 2725 (1963). (7) R. H. Busey and W. F. Giauque, J. Am. Chem. SOC.,75, 806 (1953). (8) “Physical Properties,” Bulletin No. D 763, McDanel Refractory Porcelain Co., Beaver Falls, Pa., 1963. (9) L. S. Darken and R. W. Gurry, “Physical Chemistry of Nletals,” McGraw-Hill Book Co., Inc., New York, N. Y., 1953. (10) Values for log -mawere calculated by
from data for
aIn.
MEASUREMENT OF ACTIVITIES IN GALLIUM-INDIUM LIQUIDALLOYS Table I : Experimental Effusion Data for Ga-In Alloys and Derived Values of the
Effusion cell
B. B*
c
D E F G H
I J*e
we L M***
N
Orifice area at 5 O o , O om* X 100
Atom % ’
0.09568 0.1051 0.1458 0.1947 0.2000 0,3950 0.4962 0.4955 0 . .5750 0,7436 0.9583 1,0310 1.1729 1.4022
----Total
mas8 effused,
indium
Run no. l b
Run no. ZC
98.0 94.7 92.0 90.0 88.0 88.0 50.0 49.9 3.99 4.01 1.97 2.00 0.98 1.00
1350 1101 1811 2320 2962 3695 4359 3918’ 1116 1389 1203 1456 1431 1692
1087 927 1469 1924 2533 3116 3492 3455 988 1081 1502O 1216 1126 1318
g
1049
CY
Functions of Indium
X 1W-Run no. 3d
1256 1075 1702 2218 2962 3588 4024 4007 1106 1233 1128 1375 1269 1485
=
---olrn
log 71, ___
(1
Run no. l b ’ h
15 6.48 4.37 2.55 0.75 2.12 0.47 0.31’ 0.3.5 0.46 0.35 0.37 0.48 0.47
- Xrn)*
--
-
Run no. 2C‘h
Run no. 3 d 4
21 6.85 3.40 3.46 1.82 2.93 0.415 0.42 0.44 0.46 0.76’ 0.44 0.51 0.49
51 9.94 4.12 2.50 1.96 2.51 0.47 0.47 0.43 0.40 0.34 0.35 0.36 0.34
‘Expansion-of-orifice corrections were made using the coefficient of thermal expansion of 7.8 x 10-8 deg-1.9 * At 1269’K for 225.29 At 1247OK for 330.15 min. E Cells J*, K*, and M** were calibrated with pure Ga by commin. ’ At 1223OK for 434.76 min. This value is too low, because it should agree with cell G. The values parison with cells I, L, and N which were calibrated with Hg. This value is too high, because it is out of sequence both horizontally and vertically. of G and F are nearly identical in runs 2 and 3. The CY values are the final results of the iterative procedure discussed in the text.
’
’
14
I3
12 II IO 9
aIn 6 5 .5
4
.4
3
.3
2
I 0
.2
0 ,I:
.2 . 3 .4 .5 .6 .7 .8 .9 INDIUM ATOM FRACTION
1.0
Figure 1. a-function values for indium. The solid line , for each run for 0 < XI, < represents the average a ~ ,value 0.86. The solid line 0.86 < XI, < 1 is from a least-squares fit of data from all three runs to a linear equation. The ~ on shaded regions represent the uncertainty in C Y Ibased a 3% uncertainty in vapor-pressure measurements.
two runs, of restricted value, and they are given a lower weight in the evaluation of the enthalpy data. In Table I are indicated the values of arn which were calculated for each of the experimental determinations. In Figure 1 are plotted a€,,vs. Xln for the three runs. The derived activity curves are shown in Figure 2.
Discussion I n the Introduction, the particular advantages of the multiple Knudsen-cell technique for activity measurements in a binary system were pointed out. In a previous paper,2 it was demonstrated that with
IzLY 0.I
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 INDIUM ATOM F R A C T I O N
Figure 2. Activities in liquid Ga-In solutions at 1269°K were calculated using data of Figure 1. The solid line represents the calculated activities based on CYI, = 0.42 at all compositions. The dashed curve, 0.86 < XI^ < 1, represents the calculated activities based on the given straight line through the arn data of Figure 1.
sets of vapor-pressure measurements precisions as good as 1.0 and no worse than 8.975, averaging to ca. 375, were obtained under the isothermal conditions achievable in this technique. It would follow that, in a single experiment, activities may be determined at several compositions with this same level of precision since, of course, they are all relative to the same reference state. The consistent behavior of the a-function data seen in Figure 1 indicates that the expected precision was achieved. The cr function is extremely sensitive to experimental error. The activity curves in Figure 2 show positive deviations from Raoult’s law a t all compositions for both Volume 75, Number 5 March 1968
1050 components. These curves were calculated in two ways for the composition region 0.86 < XI, < 1: (1) activities calculated from the a I n data represented by the given least-squares line of Figure 1 (dashed line) and (2) activities calculated by assuming that (YI, = 0.42 (solid line). An error analysis of the LYI, data shows that the latter method is nearly permitted (see error bands on Figure 1). There is no basis for a choice between the two curves. Svirbely and Read4 have derived activity curves for the Ga-In system from their data for the Ga-In-Zn, In-Zn, and Ga-Zn systems, which they obtained from emf measurements. Their calculated data show strong positive deviations from Raoult's law behavior for Ga over the entire composition range. For indium, a strong positive deviation was derived for 0 < X I , < 0.5, and for 0.5 < XI, < 1 the activities approximated Raoult's law behavior. Svirbely and Read make only a "semiquantitative claim" for their derived activity values of Ga and In. Some excellent data for the enthalpy of mixing in this binary system recently have been determined by Bros, et ~ 1 . by ~ ~ microcalorimetric ~ 9 ~ measurements. They obtained an integral enthalpy curve which is symmetrical with respect to the mole fraction with a maximum of 265 cal. These data indicate that AH is independent of temperature from 150" to 469" within experimental error. From the integral enthalpy curve, they derived partial molar enthalpies which were also positive. The only purpose in deriving enthalpy data from the activity data is to check for inconsistencies. The enthalpy data derived1' from the activity results were found to be in satisfactory accord with Bros' results; for example, the maximum in the integral enthalpy was at ca. 2.2 kcal, but the uncertainty is probably ca. 2 kcal. From the enthalpy data of Bros6aand Bros, et u Z . , ~ ~ and the free-energy data from this study, one may cal-
The Journal of Physical Chemistry
G. J. MACUR,R. K. EDWARDS, AND P. G. WAHLBECK culate entropy data; these data are given in Table 11. The entropies of mixing are less than ideal solution values and give an indication of ordering effects in the solutions.
Table I1 : Integral Quantities for Ga-In Alloys at 1269'K XI,
1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0
AG,G
AH,^
cal
cal
0
- 1124 - 1098 - 1016 - 862 - 595
0 84 168 220 248 265 248 220 168 96
0
0
- 567 - 862 - 1016
- 1098
AS, cal deg-1
0 0.51 0.81 0.97 1.06 1.09 1.06 0.97 0.81 0.54 0
Calculated by means of AG = RT{XI, In U I , $- X G In~ UG,,) . Values of urn and aGa were obtained from Figure 2. Based on calorimetric data of Bros, et a1.68,b
Acknowledgments. The authors gratefully acknowledge the support of this research by the Air Force Office of Scientific Research through Contract No. AF 49(638)-346 and the Atomic Energy Commission through Contract No. AT(l1-1)-1029. G. J. 11.wishes to thank the Illinois Institute of Technology for a fellowship for the 1958-1959 academic year. G. J. M. and R. K. E. acknowledge the support of the Chemical Engineering Division of Argonne National Laboratory during the preparation of the manuscript.
