MAGNETIC SUSCEPTI[BILITIES OF MOLTEN Bi-BiBr3 SOLUTIONS
851 -
Magnetic Susceptibilities of Molten Bisimuth-Bismuth Tribromide Solutions'
by L. E. Topol and F. Y. Lieu Atomics International, A Division of North American Aviation, Inc., Canoga P a r k , California (Received October 28. 196.5')
Magnetic susceptibility measurements were made with a Gouy balance on the molten Bi-BiBr3 system from 250 to 620'. The susceptibilities were diamagnetic throughout and in the composition range 0 through 20 mole % Bi were temperature independent as in the Bi-BiC13 system, whereas in the 30 t o 100% metal region the susceptibilities became less diamagnetic with increasing teimperature as in Bi-BiI, solutions. The niolar susceptibility as a function of composition resembled that of the Bi-BiI, system and is described in terms of chemical entities, e.g., BiBr, or completely localized electrons in the salt-rich melts, and in terms of the free electron model in the metal-rich compositions.
Introduction I n previous magnetic susceptibility studies on molten bismuth-bismuth halide solutions, the Bi-BiC13 system over the composition range 0 to 28.5 mole % Biz and the Bi-BiI, system with 0 to 100% Bi3 Concentrations were measured. In Bi-BiCl, the susceptibilities were found to be linear with composition and temperature independent in the range 280 to 430". I n Bi-BiL melts a t 450 to 600', on the other hand, the susceptibilities varied with composition and temperature throughout. Since it is known that a t low concentrations Bi dissolves in BiCl, to form subhalides4 of the type (BiCl)z, where 2; equals one and higher integers such as four, the suaceptibility data of the salt-rich iodide system were a h o related to the formation of a monovalent subhalide 2Bi
+ BiI, = 3BiI
(1)
The susceptibility behavior in Bi-BiC13 and Bi-BiII with low metal concentrations then indicates that the equilibrium constant for reaction 1 is smaller than that for the corresponding chloride. (It is assumed that no distinction can be made here between the specific susceptibility of BiX and (BiX)z.) For metal-rich Bi-Bi13 solutions the susceptibility data were consistent with the model of a free electron gas diluted by the salt anions. The phase diagram of the Bi-BiBr, system5 appears to be very similar to that of Bi-BiC13,6 and low metal concentration bromide melts also contain the subhalide (BiBr),.' Thus a magnetic suscepti-
bility investigation of Bi-BiBr3 solutions should afford an interesting comparison between the different bismuth systems a t low metal compositions. In addition, since the consolute temperature of the bromide system, 538°,5 is much lower than that of the chloride, 78OoI6 the entire composition range can be covered a t temperatures where vapor pressures are not too large for Vycor containers; this will enable a comparison to be made with the iodide system a t higher metal concentrations.
Experimental Materials. The purification of bismuth3 and the preparation and treatment of BiBr35 have been described previously. Apparatus and Procedure. The susceptibility measurements were made with a Gouy balance and the apparatus and procedure were similar to those used in the iodide study.3 Samples with metal compositions of 5 to 30 mole % were equilibrated a t 450' in a rocking furnace for several hours to ensure complete solution. (1) This work was supported by the Research Division of the U. 5. Atomic Energy Commission. (2) N. H. Nachtrieh, J . Phys. Chem., 6 6 , 1163 (1962). (3) L. E. Topol and L. D. Ransom, J . Chem. Phya., 38, 1663 (1963). (4) L. E. Topol, S.J. Yosim, and R. A. Osteryoung, J . Phya. Chem., 6 5 , 1511 (1961); also C. R. Boston, G. P. Smith, and L. C. Howick,
ibid., 67, 1849 (1963). (5) S. J. Yosim, L. D. Ransom, R. A. Sallach, and L. E. Topol, ibid., 6 6 , 28 (1962). (6) S.J. Yosim, A. J. Darnell, W. G. Gehman, and S. W. Mayer, ibid., 63, 230 (1959). (7) L. E. Topol and R. A. Osteryoung, ihid., 6 6 , 1587 (1962).
Volume 68, Number 4 A p d , lQ64
L. E. TOPOL AND F. Y. LIEU
852
Samples with metal concentrations of 40 mole % or higher were equilibrated a t 600' for longer periods of time. The absence of ferromagnetic impurities was checked by testing the constancy of sample susceptibility with varying field strength. The density of a 70.0 mole yo Bi solution was measured as described elsewhere.3 Since the vapor pressures above 540" are high, frequently resulting in rupture of the Pyrex pycnometer, a measurement a t only one temperature could be obtained. This density, 6.69 g./ml. a t 543 ", was extrapolated to other temperatures by assuming a temperature dependence similar to the average of the 40 mole % and pure Bi melts.
250
300
T' C 350
400
.ooo/
Results and Discussion The specific susceptibility relation
x'
=
x' is
calculated from the
2gAw/H2ad
(2)
where g is the gravitational constant, Aw the apparent change in weight of the sample on application of the magnetic field of strength fl, a the cross-sectional area of the sample, and d the density of the solution. The density results of Keneshea and Cubicciotti for 0 to 40.0 mole % Bi-BiBr3 solutions8" and for pure Bi,8b as well as the density of a 70.0 mole % Bi melt measured in this laboratory, were used. The densities of all the intermediate compositions involved in this study were obtained from the interpolated values of the measured molar volumes of the 0 to 40.0, 70.0, and 1 0 0 ~ ' Bi solutions. The molar susceptibility x is given by x'A7 = x'(NIMI NdKz) where N 1 , N z , M I , and Mz are the mole fraction and molecular weight of the two components, respectively. The specific susceptibilities as a function of temperature for 0 to 100 mole % Bi are plotted in Fig. 1. The results for a 5% Bi solution have been omitted from the figure for the sake of clarity. For the composition range, 0 to 30% metal, the 250 to 450' temperature scale a t the top of the graph should be used; for the 60 to 100% Bi solutions the 450 to 650" temperature scale a t the bottom of the plot pertains. Susceptibilities for 40 and 50% samples were measured from 285 to 625' and are thus represented on both temperature ordinates. Duplicate samples were measured for the pure components as well as the 40 and 80% compositions; the agreement between the duplicates was good for all but the 40% solution. The susceptibility 0.005 X per g. of pure fused BiBr, is -0.265 and is essentially independent of temperature in the range 250 to 460". This behavior is similar to that of , ~ susceptibility of BiClS2but is unlike the i ~ d i d e the which exhibits a small temperature dependence. It is
+
*
The Joi~rnalof Phgsical Chemistry
also interesting that the decrease in the diamagnetic susceptibility between solid and liquid BiCl,, -0.3229 and -0.280 X lop6, respectively, and solid and liquid respectively, is BiBrB, -0.3039 and -0.265 X about the same, 13%. The specific susceptibility of bismuth was found to vary with temperature from -0.036 f 0.002 X low6a t 450'to -0.030 ==I 0.002 X a t 600" in excellent agreement with the earlier rea t 450 and 600', s u l t ~ -0.038 ,~ and -0.032 X respectively. As illustrated in Fig. 1 all the solutions are diamagnetic and a decrease in diamagnetism with increasing temperature is noted for compositions of 30% Bi or greater. The largest variation in susceptibility with temperature appears to occur in the 40 to 707' melts. Thus, it seems that for compositions of 20% Bi or less and for temperatures below 500 O the bromide system resembles the chloride magnetically, whereas for the higher metal compositions above 450 O a similarity with the iodide is evident. (It should be noted that no susceptibility measurements have been accomplished in metal-rich Bi-BiCl, melts due to the limited solubilities a t these temperatures. Such measurements would be expected to show a similar behavior as the bromide and iodide, L e . , a temperature dependence.) The dotted lines in the 50 to 80% plots represent extrapolations of the data into the two phase liquid region. For the 50 mole % composition where measurements were taken (8) (a) F. J. Keneshea, Jr.. and D. Cubicciotti, J . Phys. Chem., 63, 1112 (1959); (b) ibid., 62, 843 (1958). (9) M. Prasad, C. R. Kanekar, and L. N. Mulay, J . Chem. Phys., 19, 1440 (1951).
MAGNETIC SUSCEPTI RILITIES O F
;\/lOLTEN
853
Bi-BiBrs SOLUTIONS
-
Table I : Molar Susceptibilities and the Effect of Bi in Bi-BiBrr Melts
0 0.05 0.10 0.20 0.30 0.40 0.50 0.60 0.70
0.80 0.90 1.00
a
448.7 436.8 424.8 400.8 376.8 352.8 328.9 304.9 280.9 256.9 233.0 209.0
0 0.3 -0.1 -1.4 -5.1 80.1 - 5 . 4 69.1 -5.4 46.6c 6.0 3€i.2c 5.4 20.OC 10.5 14.OC 5.5 8.4 0
118.9 113.1 107.9 98.2 90 8
... 6.0 -1.0
-7.0 -17.0 -14.0 -11.0 10.0
8.0 13.0 6.1
0
118.9 113.1 107.9 98.2 88.2 74.8 61.8" 43.9" 32.gC 19.0~ 12.6 7.5
0 0.3 -0.2 -1.6 -2.8 -0.5 1.4 8.2 8.0 10.8 6.0 0
, , ,
6.0 -2.0
-8.0 -9.3 -1.2 2.8 14.0 12.0 13.0 6.7 0
l18,gc 0 113.lC 0.2 107.9' - 0 . 2 98.2' - 1 . 8 85.5' - 0 . 3 68.8 5.2 6.6 56.2 10 4 41.2 10.9 29.5 11.2 18.0 11.2 6.7 6.7 0
... 4.0 -2.0 -9.0 -1.0 13.0 13.0 17.0 16.0 14.0 7.4 0
118.gC 0 113.lC 0.2 1O7.gc - 0 . 3 98.2C - 1 . 9 2.1 82.90 9.5 64.2 10.2 52.3 12.7 38.4 15.0 25.8 11.8 16.7 7.4 9.8 0 5.9
... 4.0 -3.0 -9.5
7,'O 24.0 20.0 21.0 21.0 15.0 8.2 0
-+-
0 = NIMl N,M:!. b A x = x - (Nlxl $. N2x2),where - A X and + A X indicate deviations in diamagnetic and paraniagnetic directions, respectively. c Extrapolat?ed value.
both below and above this immiscibility region, it is difficult to ascertain if the data are continuous; i.e., the slopes of the two sets of data appear t o be somewhat different and susceptibility values of -0.291 and -0.284 X 10-6, respectively, are found a t 450" by extrapolation of the measurements from below and above the two-phase region. Since the slopes of the 30 to 70% compositions in Fig. 1 are greater than those of the pure components, it appears, as in the Bi-Bi13 system, that one or more new species are formed. Furthermore, in order to be consistent with these data, these new species must be paramagnetic or less diamagnetic than the pure components and their concentrations must increase with temperature in the 30-70% Bi melts. Typical molar susceptibilities as a function of composition are given a t 350 O , 450 a , 550 ",and 650 " in Table I. For the 0 to 30 mole % Bi solutions a t 550 and 650" as well as for those compositions that are in the twophase liquid region (60-90% Bi a t 350" and 50430% a t 450 ") hypothetical susceptibilities were taken from extrapolated data in Fig. 1. The A x data, where A x - xsoln- (Nlxl Nzxz),indicate negligible deviations from simple additivity a t all temperatdres for melt compositions of 5 to 20 mole % Bi. At the higher metal compositions deviations occur a t first in a more diamagnetic direction from additivity and then in a more paramagnetic direction. The diamagnetic deviations decrease in magnitude as the temperature is increased and a t temperatures of 550" and above are virtually nonexistent. On the other hand, the paramagnetic deviations increase with increase in temperature. These effects are accentuated by comparing the deviations from additivity per addition of metal, Ax/Nsi
(Table I), and here again, as in the Bi-BiL system, a maximum paramagnetic effect is found a t all temperatures around a composition corresponding to a Bianion ratio of unity. As discussed previously, the negligible deviations from additivity in melts of low metal concentration should not be taken to indicate that little or no interaction occurs between the components. Since bulk metals consist of cations and free electrons, the additive susceptibility behavior (see eq. 9 and 10) would be expected to follow that represented by curve 5 in Fig. 2 . Furthermore, since strong interactions resulting in the new species, (BiBr)z, are known to occur in this system,' an interpretation of these results must be
+
o
010
oao
030
040
a50
