TRANSPORT PROCESSES IN Low MELTIICG SALTS
Transport Processes in Low Melting Salts.
4025
The AgN0,-TlNO, System
by G. J. Jam,* R. P. T. Tomkins, H. Siegenthaler, K. Balasubrahmanyam, and S. W. Lurie Depurtment of Chemistry, Rensselaer Polytechnic Institute, Troy, A7ew York
12282
(Received June 1 , 2971)
Publication costs borno completely by The Journal of Physical Chemistry
An investmigation of the viscosity and conductance and the laser Raman spectrum for molten mixtures of AgKOs and 'LllS0~is reported. The absence of new frequencies and the temperature iiivariaiice of the intensities for the observed Raman bands indicate t'hat the symmetry of the NOs- ion in t'he mixtures does not differ significantly h o m that of the NOa- in the parent compounds. The "back-donation of electrons" from cations into the R system of the Koa- ions appears lesseued in the molt'en mixtures, and this effect is greatest at the equimolar mistures. From the viscosities, it is found that the simple mole fraction viscosit'y relat'ionship is very nearly obeyed ; i.e., t8hepolarization interact'ionsare virtually zero, a i d the mixt'ures are thus nearly ideal. The clectrical coiiductances of the mixtures can be accounted for if a term is introduced for ionic association, but in these mixtures this is found t'o be less than 4%. The results thus confirm small but finite noncoulombic contributions to the structural features and transport processes in such molten elect'rolytes. The phase diagram for the AgT\'O3-T1P\'O3 system shows1 the features of two low melting eutectic mixtures (52 mol % TlN03, mp 82.2'; 45 mol % T1S03, mp 52.5') and a low melting compound of equimolar composition (mp 83'). There is, thus, the opportunity to investigate the liquid state properties of such mixtures from relatively low temperatures to temperatures where both the parent compounds themselves are molten (e.g., AgKOa, mp 210'; TlN03, mp 205"). I n this communication, an investigation of the properties of viscosity and conductance of this system is reported from this viewpoint; the results are examined from the viewpoints of polarization and ionic size effects, together with some results from laser Raman spectroscopy. Experimental and Results Section For AgNO, and Tln'O3, NSRDS recommendations for viscosities, electrical conductance, and densities have been advanced recently2 from critical assessments of the collected published data; the temperaturedependent equations are given in Chart I. The acChart I
Ag??03 viscosity conductance density
7 = -?K
=
(A = P =
11.59 X exp(3620/RT) cP 11.745 exp(-2749/RT) W 1cm-I 587.9 exp( - 2898/RT) C2-l om2 4,454 - 1.02 X 10-3T g 0111-3 TlNOa
viscosity
rl =
conductance density
P =
8.430 X exp(3657/RT) CP 9.416 exp(-3143/RT) W-' cm-1 633.25 exp(-3348.3/RT) W-l cm2 5.8041 - 1.8737 X 1 O - T g cmF3
curacies are estimated to be within the limits of 0. 15-0.3y0 (density), 0.7-1 .OyO (conductance) and approximately 1.0% (viscosity). ~
For binary mixtures of these two components, four investigations have bcrn reported: Rabinowitsch (1921),3 Sandonnini (1920),4 Bolihovltin (1949),5 and Brillant, et al. (1966, 1968).'j The measurements of Rabinowitsch were limited to one composition (50 mol 70-4gn'Oa) and a single temperature (373'K). The results of a critical evaluation of the latter two studies may be summarized as follows. Density. The results of Bokhovkin5 and Brillant7 are at different compositions so that no direct comparison is possible except of the values for the single components. Such a comparison shows that the results of Brillant deviate somewhat less from the XSRDS recommended values2 than those of Bolihovliin (approximately 0.2 and O.S%, respectively). A statistical analysis of the results of Brillant' was undertaken to express the data simultaneously as a function of composition (c) and temperature ( T , 'K). The equation, thus derived, is p =
5.80573
-
1.86467 X 10-3T - 1.10779 X
lO-*C
+ 7.24708 X lO-'jTC
(g ~ m - ~ )
and may be used within the temperature range of 435635'K, with a standard error of about 0,07% relative to the published data; the maximum departure is 0.2% and is noted at 485°K for the results reported for the 60 mol % Agr\'Oa mixtures. (1) C. VanEyck,Z.Phys. Chem. (Leipig),51,721 (1905). ( 2 ) G. J. Jam, F. W. Darnpier, G. R. Lakshminarayanan, P. K. Lorenz, and R. P. T. Tomkins, "Molten Salts," 5'01. 1, NSRDS-XBS 15, U. S. Government Printing Office, Washington, D . C., Oct 1968. (3) A . J . Rabinowitsch, 2. Phys. Chrm. (Leipzio),99,417 (1921). (4) C. Sandonnini, Gnzz. Chem.Ital., 50, 289 (1920). (5) I. I. Bokhovkin, Zh. Obsch. Khim., 19,805 (1949). (6) LM.Bakes, 5. Brillant, J. Brenet, J. DuPuy, J. Guion, Y . Nakamura, and J. Ruch, J . Ckim. Phps., 63, 1491 (1966). (7) S.Brillant, Ph.D. Thesis, Strasbourgh (1968); J. Chim. Phys., 65,2138 (1968). The Journal o j Phu/sical Chemistry, Vol. 76, No. $6, 1971
4026
JANZ, TOXKINS, SIEGENTHALER, BALAXUBRAHNANYARI, AND LUIIIE
Conductance. Results reporteds-' for the single components compare with thc NSRDS recommcndcd values as follows Investigator
Deviation for NSRDS values
Sandonnini (1920) Bokhovkin (1949) Brillant 11968)
AgXOs ( 2 . 2 % ) ) TIN03 (4 47,) AgN03 (4,9%); TISO, (3.3%) ( 0 . 6 2 4 ~ ) ;TlNOs (0 60%)
For the binary mixtures, accordingly, the work of Brillant' is recommended; results for the single components and for five binary mixtures (containing 21, 35, 50, 70, and 90 mol % T l r o , ) were reported' and need riot be detailed here. The derivation of an expression giving these results simultaneously as a function of temperature and composition (cf. density, preceding) 1% as undertaken, but this worli was without success. Viscosity. The investigations appear limited to the studies of Bolchovlcin6in xhich viscosities were reported for 13 binary mixtures (6.8 to 85.4 mol % TIT\'(),; 395498°K) and the single components, and that of Rabinonitsch3 (one data point for 50 mol % TNO3 at 373°K). A comparison x i t h the KSRDS value for molten T1N03 shows that the Bokhovliin result deviates by approximately 5%, and the estimate of uncertainty for the results of the binary mixtures is thus difficult without additional input. One of the eutectic mixtures (45 mol yo TINO,; mp 82.5") was selected for further study because of the largcr temperature range available. The eutectic mixture (above) was made up by weight from certified reagent grade chemicals which had been recrystallized from double-distilled water and oven dried (25", 24 hr; l l O o , 12 hr). All transfers of the dried chemicals were by desiccator techniques, in a dry Nz glove box, or by vacuum manifold techniques. The viscosity measurements were with the modified Ostwald-type viscometer of this laboratory. Details of the design, the calibration procedures, and the silicone oil bath (160-250')) and molten salt bath (260-310') have been given elsewhere by Timidei, et aZ.8 All viscosity measurements were repeated at least three times to cross-check reproducibility of the flow times (+0,5%), and the temperatures were increased and decreased at random in the cycle to evaluate the temperature dependence of the viscosity data. The results are in Table I for the range investigated (160-3 10'). Table I: Viscosity Data for AgNO3-T1N03 Eutectic Mixture T , OK 7,cP T , OK 7,
CP
T,
O K
7, CP
433 7.441 493 4.027 553 2.742
443 6.523 503 3.714 ,563 2.578
453 5.863 513 3.461 573 2.427
463 5.263 523 3.215 553 2.320
473 4.712 533 3.081
T h e Journal of Physical Chemistry, Vol. 76,hTo.$6, 1971
483 4.384 543 2.900
The temperature dcpcndrncc of thcsc rcsults w s analyzcd by thc Arrhrnius-type rxponcntinl rrl :L t'ion and a power-scrim equation. The rrsults arc givcri by this expression 7 =
122.59 X
exp(3407,2/RT) cP
for the range of 503 to 5S3"1
