96
J. Chem. Eng. Data 1988, 33, 96-98
of the adducts showed that most of them decompose on heating. To evaluate the relative strengths of arsenic-nitrogen bonds, it was necessary to assume that the molar enthalpy of sublimation of each adduct was equal to the enthalpy of vaporization of 1 mol of ligand (34, 35). Standard enthalpies of sublimation of several adducts (that could be measured) and its respective ligands, confirmed our assumption (36-38). For adducts of the same stoichiometry, ~ ( A s - N )values also follow the sequence py < /3-mpy < y-mpy. ArHe(g) and ~ ( A s - N ) values are listed in Table V. Comparison of the same base with different acids gives the acidity order ASCI, > Asl, as is expected from the electronegativity values of chloride and iodine atoms. I n synthesis, the A,He and other parameters data indicate that the As-N bond is stronger as we go in the sequence py < /3-mpy < y-mpy. The substitution of one hydrogen in the pyridine ring by the electronic donator methyl group causes the increase of the electronic density in the aromatic ring and consequently the electronic density on the nitrogen atom. I t is then expected that the electronic density available for bonding is higher in 0-mpy and y-mpy than in py. The order observed between 0-mpy and y-mpy is due to the stronger inductive effect of the p-methyl than the m-methyl group. On the other hand, for a given ligand, the stronger bond is formed with the stronger acid as is also shown by the data on the A,He and other parameters. Reglotry No. Py, 110-86-1; P-mpy, 108-99-6; y-mpy, 108-89-4; AsCI,.py, 112070-05-0: AsCI&-mpy, 112087-35-1; AsCI,.y-mpy, 112070-10-7; 2AsBr3.3py, 1 12070-08-3; AsBr,BP-mpy, 112070-07-2: AsBr3-2y-mpy, 112070-06-1; As13.2py, 94503-44-3; AsI,$-mpy, 112070-09-4; AsI,-y-mpy, 112070-1 1-8; ASCI,, 7784-34-1; AsBr,, 7784-33-0; ASIS, 7784-45-4.
Literature Cited Loh, R. T. C.; Dehn. W. M. J. Am. Chem. SOC. 1928, 4 8 , 2956. Dafert. 0.; Mellnski, Z. A. Ber. Dtsch. Chem. Ges. 6 1928, 59, 788. Holmes, R. R.; W a n t , E. F. J. Am. Chem. SOC. 1958, 8 0 , 2980. Lindqulst, 1. Inorganic AWuct Molecules of Oxo-compounds; Springer Verlag: West Berlin, 1983. (5) Deveney, M. J.; Webster, M. J. Chem. SOC.A 1970, 1643. (6) Webster, M.; Keats, S. J. Chem. SOC.A 1971, 836. (7) Gibson, C. S.; Johnson, J. D. A.; Vining, D. C. J. Chem. Soc. 1930, 1710. (1) (2) (3) (4)
(8) Shirey, W. 6. J. Am. Chem. Soc. 1930, 52, 1720. (9) Kondratenko, 6. P. J. Gen. Chem. (USSR) 1934. 4 , 246. (10) Montlgnle, E. Bull. SOC.Chhn. 1935, 5(2), 1365. (11) Gill, N. S.:Nuttan. R. H.;Scaife, D. E.: Sham, D. W. A. J. Inorg. Nucl. Chem. 1981. 18, 79. (12) Graddon, D. P.; Watton, E. C. Aust. J. Chem. 1985. 18, 507. (13) Giesse, R.; Gushikem, Y.; Volpe, P. L. 0. Thermochim. Acta. 1982, 54. 257.
(14) Pau1,R. C.; Kaushal, R.; Pahil, S. S. J. Indian Chem. SOC. 1989, 46(1). 26. (15) Paul, R. C.: Slngh, P.: Dhlndsa, K. S.;Chadha, S. L. Indian J. Chem. 1970, 8(11), 1014. (16) Parkash, R.; Ahkrwalia, S. C.; Sud,S. C.; Sahni, R. N.; Paul, R. C. Monatsh, Chem. 1981, 112(6-7), 707. (17) Oddo. G.; Glachery, U. Gazz. Chlm. Ital. 1924, 5 3 , 56. (18) Baihr, J. C. Inorg. Synth. 1939, 1, 103. (19) Vogel, A. 1. A Text Book of Quantitative Inorganic Analysis; Pergamon: Oxford, U.K., 1973. (20) Kolthoff, I. M.; Sandell. E. B. Tratado de Analltica Cuantitafiva, 3rd ed.; Libreria e Editorial Nigar, S.R. L.: Buenos Alres, 1956. (21) Jorge, R. A.; Alrokli, C.; Chagas, A. P. J. Chem. SOC..Dalton Trans. 1978, 1102. (22) '241, N. S.;Nuttall, R. H.; Scaife, D. E.; Sharp, D. W. A. J . Inorg. "9. Chem. 1981, 18, 79. (23) Bellamy, L. J. J. Chem. SOC. 1955, 2818. (24) Kross, R. D.; Fassel, V. A,; Margoshes, M. J. Am. Chem. Soc. 1958, 78, 1332. (25) Gaddon, D. P.: Watton, E. C. Ausf. J. Chem. 1985, 18, 507. (26) Gill, N. S.; Klngdon, H. J. Aust. J. Chem. 1988, 19, 2197. (27) Wagman, D. D.; Evans, W. H.; Parker, V. 6.; Schumm, R. H.; Halow, 1.; Bailey, S. M.; Churney, K. L.; Nuttail, R. L. J. Phys. Chem. R e f . Data 1982, 11, 2-77. (28) Karapet'yants M. Kh.; Karapet'yants, M. L. Thermodynamic Constants of Incfganic and Organic Compounds;Ann Arbor-Humphrey: London, 1970. (29) Pedley, J. 6.; Rylance, J. Sussex-N.P.L. Computer Analysed T h e m chemical Data : Organic and Organo -Metallic Compounds ; Sussex University: Brlghton, England, 1970. (30) Akoldi, C. Inwg. Chem. 1981, 20, 998. (31) Wilson, J. W.; Worrai, I. J. J. Inorg. Nucl. Chem. 1989, 31, 1357. (32) Goncalves, A. S.: Chaaas, A. P.; Alroldi, C. J. Chem. Soc.. Dalton Trans. 1979, 159. (33) Jorge, R. A.; Alroldi, C.: Chagas, A. P. J . Chem . SOC., Dalton Trans. l.a- .m-, 1102 . . - -. (34) Simonl, J. A.; Airoldi, C.; Chagas, A. P. J. Chem. Soc.,Dalton Trans. 1980, 156. (35) Airoldi, C.; Chagas, A. P.; AssuncHo, F. P. J. Chem. SOC., Dalton Trans. 1980. 1823. (36) Burkinshaw, 'P. M.; Mortimer, C. T. Coord. Chem. Rev. 1983, 48, 101. (37) Burkinshaw, P. M.; Mortlmer, C. T. J. Chem. SOC. Dalton Trans. 1984. 75. (38) Ashcroft, S. J.; J. Chem. SOC.A 1970, 1020. Received for review October 2, 1986. Accepted July 24, 1987. We thank CNPq and FAPESP for financial support.
Solid-Liquid Equilibria in the Reciprocal Ternary System K,Li/S,C03 Kevkr Babcock and Jack Wlnnlck" School of Chemical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0 100
The solld-llquld equfflbrla in the molten salt system K,LUS,C03 were studied as a function of compodtlon and temperature. The ioweld freezing-meltlng mixture of the reciprocal ternary system lies within the region bordered by the following selected four points: XK# = 0.20, XK,cO, = 0.40, Xuzcos= 0.40; XKa = 0.20, XK,CO, = 0.32, X~~,co, = 0.48; XK8 = 0.12, XKzCO, = 0.45, XLhcOa= 0.43; and X K =~0.09, XK,CO, = 0.32, Xu,co, = 0.59 at 485 OC. The preclsion of the ilquidus temperatures is f10 O C . Introduction Data concerning phase diagrams of reciprocal ternary systems, mixtures containing two cations and two anions, have 0021-956818811733-0096$01.5010
received attention in recent years. Among the different measurements, those on solid-liquid equilibria are particularly important for use in fuel cells. Solid-liquid (SL) equilibria are reported, relatlve to the reciprocal ternary system K,Li/S,CO,. To our knowledge, no data for this system have been previously reported, except llquidus data concerning the binary system (K,Li/CO,), which have been measured by Janz and Lorenz ( I ) . Experlmental Section Commercially available samples of K2S, Li2S, K2C03,and Li,C03 (Alfa) were used for preparation of the binary and ternary mixtures. Particular care was devoted to the purification and drying of the salt components. The K2S was of 44% nominal purity, the principal impurities being polysulfides as weli as hydrates of the polysulfides. The method of purification 0 1988 American Chemical Society
Journal of Chemical and Engineering Data, Vol. 33, No. 2, 1988 97 110
Y
_ -. 7
I
li0?------
I
1 \
60
0
05
4001 0
IO
MOLE FRACTION
Figure 1. Liquidus temperatures for the binaries (Li,S
(K2C03
-
+ Li2C03),
+ Li2C03): 0 are experimental data for (Li,S + Li,CO,);
+
0
are experimental data for (K2C03 Li,CO,); A are representative data points for (K,C03 Li2C03)from Janz and Lorenz (7).
+
involved heating the K,S to temperatures as high as 1000 OC in a hydrogen atmosphere. The hydrates and polysulfides were presumed removed by the bubbled hydrogen upon heating to 1000 oc. The product of this procedure, taken as pure K,S, melted at 840 f 10 OC. Accepted values for the melting point of K2S range from 835-840 OC ( 2 , 4 )to 948 OC (5), depending, apparently, on purification technique; the highest value, 948 OC, was arrived at from the K-K,S system (5). Our procedure, starting with sulfur-rich material, yielded a melting point in closer accord with the lower values (2-4). The other individual components (of f99 % purity) were dried to constant weight under either an H, N, CO, or argon atmosphere at a maximum furnace temperature of 1000 OC, and stored over CaSO, in desiccators until used. The high-temperature tubular furnace employed in this study has been described in detail elsewhere ( 6 ) ,with the furnace height being shortened. Type K (chromel-alumel) uncalibrated thermocouples were used as the input for a proportional temperature controller (Barber-Coleman Model 122A). The temperature at any point in the furnace could be controlled to 5 OC. The main experimental technique was visual observation of the liquidus, on both heating and cooling. Some points were checked by using an ac-impedance bridge (7)with gold electrodes suspended in the melts. The sulfide-carbonate materials were weighed as quickly as possible in air in milligram amounts in the exact stoichiometries required for the mixtures, and were transferred to a desiccator. All transfers were performed in a dry argon atmosphere, except when transfered from desiccator to the furnace. Possible contamination through trace impurities is minimzed in this preparative method. The samples thus prepared were then conditioned in alumina crucibles under an argon atmosphere, before measurements, by repeated thermal cycling (from 1 to 50 OC/min) through the metting-crystallization range by using the furnace setup. Some reaction was noticed with the alumina during the purification of the potassium sulfide. The prefused eutectics and selected ternary mixtures were visually observed for the first crystals on freezing or last crystals on melting. The visual method and ac impedance method were used for checking the pure components and the K,Li/CO, system; the methods agreed fairly well, to roughly A10 OC. The precision limit for the liquidus temperature measurements, based on replicating the main diagonals and four ternary cuts three times each, is at worst f10 OC. The only seeded samples were the eutectics, identified by Janz and Lorenz, for the K,Li/CO, system. All other samples were not observed to undergo supercooling, as the temperatures recorded during the
0'5 MOLE FRACTION
Figure 2. Liquidus temperatures for the binaries: 0, (K,S (K,S KZCOJ.
+
1I O + Li,S);
0,
Figure 3. Polythermal projection, reciprocal ternary: (K,Li),/S,CO, E, eutectic; M, minimum-melting mixture. Note: Congruently melting (Li/K),CO, at -510 O C ( 7 ) is not shown.
heating/cooling thermal cycling process agree within 10 OC. Results and Dlscusslon General features of the binary and ternary solid-liquid equilibrium are qualitatively confirmed, with the phase diagram being comprised of 995 liquidus temperature points of various binary and ternary compositions. Figures 1 and 2 report the SL equilibria temperatures of the four binaries K,Li/S, K/S,CO,, Li/S,CO,, and K,Li/C03 which represent the four sides of the composition square, listed below: K2S Li,S: eutectic at XKzS = 0.43 and 745 OC; K2S K,CO,: eutectic at XKzS = 0.60 and 625 OC; Li2S Li,CO,: a continuously melting-freezing curve with the sole solids being the pure salt components; K,C03 4- Li,CO,: eutectics at XLIzCo3 = 0.62 and 492 OC; and Xu,co, = 0.42 and 503 OC. The experimentally determined K,Li/C03 binary liquidus temperatures compare favorably with those of Janz and Lorenz ( 7 ) , with the maximum difference being 13 OC. They however, observed a congruently melting 1:l compound, which we were not able to confirm. The general topology of the reciprocal ternary system is shown in Figure 3,which represents the four binary liquidus data
+ +
+
Q8 Journal of Chemical and Engineering Data, Vol. 33, No. 2, 1988 Table I1
Table I. Liquidus Temperatures ("C) in the System K,Li/S,C08n Stable Diagonal: K2S + Li2C03
X K ~ S T,OC 0.000 0.100 0.200 0.300
722 730 730 695
X K ~ S T,"C
XK2S
T,"c
0.400 0.500 0.600 0.700
0.800 0.900 1.000
710 800 840
665 625 615 635
Unstable Diaeonal LLS
0.000 0.100 0.200 0.300
902 800 615 550
-AG,O,
0.400 0.500 0.600 0.700
550 625 750 810
860 950 1025
X ~ i ~ sT,OC
T,"C
0.000 0.100 0.200 0.300
X L ~ ~ ST,"C XLi2s Cut a: Li2S + (K2S-K2C03(0.2)) 725 0.400 800 0.800 695 0.500 785 0.900 790 0.600 775 1.000 800 0.700 820
870 950 1025
0.000 0.100 0.200 0.300
Cut b: LizS + (K2S-KzCO3(0.5)) 625 0.400 725 0.800 590 0.500 740 0.900 585 0.600 765 1.000 600 0.700 820
870 945 1025
0.000 0.100 0.200 0.300
Cut c: Li2S + (LizCO3-KzC0&0.5)] 510 0.400 770 0.800 490 0.500 800 0.900 565 0.600 840 1.000 645 0.700 870
920 975 1025
0.000 0.100 0.200 0.300
Cut d: Li2S + (LizCO3-K2CO3(0.2)) 640 0.400 830 0.800 685 0.500 855 0.900 750 0.600 880 1.000 795 0.700 905
955 1000 1025
0.000 0.100 0.200 0.300
815 805 680 610
0.800 0.900 1.000
770 840 902
0.000 0.100 0.200 0.300
Cut f K2C03+ (K2S-Li2S(0.5)) 790 0.400 585 0.800 795 0.500 555 0.900 1.000 790 0.600 565 675 0.700 600
730 820 902
0.000 0.100 0.200 0.300
Cut g: K&03 + {Li2C03-Li2S(0.5)) 875 0.400 610 0.800 840 0.500 525 0.900 1.OOO 810 0.600 485 745 0.700 565
650 790 902
0.000 0.100 0.200 0.300
Cut h: K2C03+ (Li2C03-Li2S(0.2)) 805 0.400 550 0.800 0.500 500 0.900 770 700 0.600 520 1.000 615 0.700 600
735 810 902
585 620 725
Li,COI 1322.5 1370.6
Li,S 516.6 545.8
kJ/mol K,COI 1312.6 1375.4
K,S 527.3 567.8
-AGR""
20.6 17.2
Reaction 1.
+
+ KXO, 0.800 0.900 1.O00
0.500 0.600 0.700
T, K 800 1000
are represented by isotherms. The K2S Li,C03 axis coincides with the stable diagonal (9)which was calculated (see Appendix) from available Gibbs free energy data from Barin and Knacke (IO).The lowest freezing-melting mixture of the r e ciprocal ternary system lies within the region bordered by the following selected four points, as shown in Figure 3: XKzS= 0.20, X K z C 0 3 = 0.40, Xupo, = 0.40; X K P s = 0.209 X K Z c o 3 = 0.21,X L I p o , = 0.48;X K z S = 0.12, X K 2 c 0 3 = 0.45, X L i 2 c 0 3 = 0.43; and X K P S = 0.09, XK2CO3 = 0.32,XLI,cO, = 0.59 at 485 OC. The reciprocai ternary diagram, Figure 3, with the stable diagonal along the K,S 4- Li2C03axis meets the criteria for these systems as described by Ricci ( 11). The high reactivity and thermal instabillty of molten alkali metal carbonates and sulfides undoubtedly contribute to uncertainties in published data for these salts. The results presented here indicate the complexity of these mitures and demonstrate the need for further refinement.
Appendlx The stable diagonal was calculated for the metathetic reaction Li2S
+ K2CO3 = K2S + Li2C03
(1)
by using Gibbs free energy data from Barin and Knacke (6). The free energy data and the calculations are summarized in Table 11. Based on the calculated AGO values, the methathetic reaction goes from left to right, resulting in the K,S Li,C03 stable pair.
+
Registry KPCO,,
No. Li,S,
12136-58-2; Li,C03, 554-13-2; K,S,
1312-73-8;
584-08-7.
Llterature Cited
The X values are mole fractions. and the projections of the 96 liquidus ternary cuts along with the temperatures of the corresponding eutectics. Table I reports the SL equilibria temperatures along the two diagonals and the eight selected off-diagonal cuts in a manner similar to that of Flor et al. (8). Data for the 96 liquidus cuts across the field of the ternary are summarized in Figure 3 and
Janz, G.; Lorenz, M. J. Chem. Eng. Data 1961, 6 , 321. Kubaschewski, 0.; Evans, L. L.; Alcock, C. E. Metallurglcal Thermochemistry; 4th ed.; Pergamon: Oxford, 1967. Weast, R. C. Handbook of Chemistry and Physlcs, 67th ed.; CRC: Boca Raton, FL, 1986. Goubeau, V. J. et al. Z. Anorg. Ailg. Chem. 1938, 236, 45. Dworkin, A. S.; Bredig. M. A. J . Phys. Chem. 1967, 71, 764. White, K.; Wlnnick, J. Electrochim. Acta 1985, 30 (4), 51 1. Bard, A.; Faulker, L. Electrochemical Methods; Wiiey: New York, 1980; p 317. Fior, G.; Margheritis, C.; Sinistri, C. J . Chem. Eng. Data 1979, 2 4 , 361. Franzosini, P.; Sanesl, M. Thermodynamic end Transport Properties of Organic Salts; Pergamon: New York, 1980; p 221. Barin, I.; Kmcke, 0. Thermochemical Properties of Inorganic Substances ; Springer-Veriag: Berlin; 1973. Ricci, J. The Phase Rule and Heterogeneous Equilibrlum: Van Nostrand: New York, 1951.
Received for review September 18, 1986. Revised August 18, 1987. Accepted January 5, 1988.
