1774
C. W. BJORKLUND, J. C. REAVIS,J. A. LEARYAND K. A. WALSH
which is equivalent to 1.
F>> 1
>> (4Aki + ~.*[S]')-'/I
(A8) (~8')
Vol. 63
Hence the steady-state treatment to this system appears to be justified since the time taken here to reach i t is oven shorter than before.
PHASE EQUILIBRIA IN THE BINARY SYSTEMS PuCl3-NaCl AND PuC13LiCl1I2 BY C.W. BJORKLUND, J. G. REAVIS,J. A. LEARYAND K. A. WALSH Contribution from the University of California, Los Alamos Scientific Laboratory, Los Alamos, New Mexico Received April 18, 1969
Equilibrium diagrams for the binary systems PuC13-LiCl and PuCls-NaCl were studied over the temperature range 100825' by thermal and differential thermal analysis techniques. A single eutectic was observed in each system with no evidence of solid solution or compound formation. The eutectic occurred a t 461' and 28 mole % ' PuC13 in the PuClt-I,iCl system and at 453' and 36 mole % PuCL in the PuCla-NaC1 system. The melting points of LiCl, NnCl and PuCL in equilibrium with an atmosphere of anhydrous HC1 were 607 f 2", 802 f 2' and 767 =t2", respectively. Within experimental error, the same values were obtained for the melting points of these salts under vacuum.
Introduction Information concerning the equilibrium diagrams for the binary systems PuCl3-LiC1 and PuC13-NaC1 was required for a proposed study of fused salt methods for processing irradiated plutonium-alloy fuels. Since only the melting points of the three compounds have been reported, it was necessary to investigate the entire composition range in both systems. The techniques of thermal and differential thermal analysis were adopted for this work. Although the terms melting point and freezing point are used synonymously in this paper, all data are based solely on freezing points obtained from cooling curves. Experimental Materials.-LiC1 was purified in the quartz apparatus shown in Fig. 1. The evacuation-hydrochlorination technique developed by Laitinen, Ferguson and Osteryounga for the preparation of LiCI-KCl eutectic mixtures was adapted for this purpose. The purified salt was then cast in the form of rods 4-14 mm. in diameter and was stored in an atmosphere of dry argon. Since molten commercial LiCl invariably waa discolored by a sus ension of black particles,4 it was necessary to filter the sa& between the hydrochlorination and casting steps. The equipment was designed so that the entire purification procedure could be carried out without exposure of the LiCl to atmospheric moisture. I n a typical procedure, LiCl (Mallinckrodt, analytical reagent grade) was dried by evacuation (0.05-0.1 mm.) a t room temperature for a period of 48-72 hr. Evacuation was continued for a 12 hr. period during which the temperature was increased to 400' a t O.S'/min. Anhydrous HC1 was then admitted a t a flow rate of 3 l./hr. through the filter tube embedded in the powder as shown in Fig. 1, and the temperature was raised to 650' a t l'/min. The salt melted a t -607:. The flow of HC1 was continued for 30 min., after which argon was bubbled through the melt for 5 min., and the system was evacuated. Argon pressure was then used to force part of the molten salt successively into the filter tube and into the casting tube. The filled casting tube was raised to the cooler (1) Presented at the 135th meeting of the American Chemical Society in Boston, April, 1959. (2) This work was done under the auspices of the Atomic Energy Commission. (3) H. A. Laitinen, W. S. Ferguson and R. A. Osteryounp. J . Electrochen. SOC.,104, 516 (1957). (4) Some tiny blaok specks could also be observed in unopened bottles of analytical reagent grade LiCI. Suspensions of black particles observed in molten LiCI-KC1 mixtures by C. T. Brown, H. J. Gardner, C. Solomons and G. J. Jan8 (NP-6483, Oct., 1957) were attributed to organia impurities which they suggested might decompose with heat in the same manner 85 sugar t o give carbon and water.
upper region of the filter tube to permit the LiCl to solidify completely. Additional castings were made by exchanging casting tubes. To prevent the entry of air during this exchange, a positive pressure of argon was maintained in the filter tube. The system was then evacuated, and the procedure was repeated. After their removal, the filled casting tubes were sealed with a torch and were stored in an atmosphere of dry argon. Two modifications of the LiCl purification procedure were also tested. In one modification, LiCl prepared by the procedure described above was distilled under vacuum a t 750'; in the other, commercial analytical reagent grade LiCl was recrystallized from aqueous solution prior to the evacuationhydrochlorination-filtration procedure. Qualitative spectrographic analyses were obtained for samples of each product. The results are given in Table I.
TABLE I QUALITATIVESPECTROQRAPHIC ANALYSESOF PURIFIED LiCl SAMPLES Element
Filtered and Filtered LiCI, % dist.illed LiCI, %
-
Recrystallized and filtered LiC1, ?&
NO.1 0.01-0.1 < .001 ND" .01 < .001 .001- .01 < .001 < .001 < ,001 0.001-0.01 0.001-0.01 .001- .01 K ND 0.001-0.01 ND ND = not detected. Other elements not detected: Ag, AI, B. Ba, Be., Bi, Cd, Co, Cu, Cr, In, Mn, Mo, Ni, P , Pb, Sb, Sn, Sr, Ti, V, Zn, Zr.
Na Mg Ca Si Fe
NO.1
.01
N
(I
A significant result of the purification procedure, in addition to the removal of carbonaceous material, was the elimination of constituents which promoted etching of the quartz containers. Purified LiCl could be held in quartz vessels under dry HC1 or argon for several days a t 650" with no appreciable effect on the vessels. Molten LiCl which had been dried a t room temperature but which had not been treated with HC1 etched the quartz vessels severely within a few hours. Corrosion was most pronounced on surfaces immediately above the melt. PuC13 was prepared from plutonium hydride by reaction with anhydrous HCI a t 450'. The hydride was obtained by reacting pure plutonium metal with hydrogen a t about ZOO'. Since PuC13 preparcd in this manner may still contain small amounts of oxide, hydride or unreacted metal, the PuCls used in these experiments was subjected to further treatment. Anhydrous HCl was passed through the PuC13 powder in the quartz apparatus shown in Fig. 1 as the temperature was increased to 800" at 2-4'/min. The stream of HC1 was bubbled through the molten salt a t 800' for 45 min., after which the PuC13was filtered and cast by the same procedure used in the LiCl preparation. Analytical data for
Oct., 1959
PHASEEQUILIBRIA IN BINARY SYSTEMSPuClsNaCl AND PuClrLiC1
1775
K-
J
nI
L'
Fig. l.-purification apparatus: (A) casting tube, 60 x (0.4 to 1.4 cm.) i d . ; (B) filtration tube, 56 x 2 cm. i.d.; (C) melt container, 12 X 4.5 cm. i d . ; (D) furnace tube, 50 X 5 cm. i.d.; (E) fused salt; (F) quartz filter 15-40 porosity; (G) neoprene stoppers; (H.) nickel radiation shields; (I)thermocouple well; (J) Hevl-Duty type M2012 tube furnace; (K) fire brick support. a typical sample of the filtered PuCla are given in Table IT. The stoichiometry of the filtered salt was the same, within experimental error, as that of PuCla purified by vacuum distillation at 900'.
TABLE I1 TYPICAL ANALYSIS OF FILTERED PUc18 Element
Wt., %
Element
6 9 . 2 (=to. 1) Mg C1" 30.8(f0.1) Fe Si 0.07 Cr Ni 0.005 A1 Calcd. for PuC13: Pu, 69.20; C1,30.80.
Wt., %
PU"
a
e
0.004 .003 .OOl .001
NaCl (J. T. Baker, analytical reagent grade) was heated in a quartz tube to 825" at l"/min. in a stream of dry HCl. The HCl was bubbled through the molten salt a t 825' for 30 Inin., after which the salt was cooled and stored in a desiccator over anhydrous Mg(C104)2. Argon (Linde Air Products) was passed over hot copper turnings to remove traces of 0 2 . Both the argon and HCI (Matheson Co., 99.0% min.) were passed through anhydrous hlg(ClO& to remove any moisture that might have been present. Freezing Point Apparatus.-Cooling curves were obtained by a combination of thermal and differential thermal analysis techniques using the quartz apparatus shown in Fig. 2. The furnace tube was supported on a cylinder of fire-brick located approximately 9 in. below the top of the furnace so as to center the melt in the hottest zone. The furnace temy a t u r e was regulated by B Brown Type 153 Elektronic roportioning Controller. The detecting unit was a chro-
Fig. Z.-Freezing point apparatus: (A) differential Cr-AI thermocouple leads; (B) Cr-A1 thermocouple leads; (C) furnace tube, 38 x 5.0 cm. lad.; (D) freezing Point tubes, 45 x 1.6 cm. i.d.; (E) gas inlet tubes, upper end 3 mm. i.d., lower end 2 mm. 1.d.; (F) thermocouple wells, 4 mm. 1.d.; (G) fused salt; (H) LiC1-KCleutectic; (I)neoprene stoppers; ( J ) nickel radiation shields; (K) Hevi-Duty type M2012 tube furnace; (L) fire brick support. mel-alumel thermocouple located between the furnace winding and the quartz furnace tube with the thermocouple bead a t approximately the same level as the fused salt. A Brown Elektr-0-Line Relay with automatic reset operated from the controller to vary the position of a Beck No. 2521 proportioning motor which, in turn, drove the 7.5 k.v.a. Powerstat transformer which furnished power to the furnace. Linear heating and cooling rates from 0.4 to 8.3'/min..were obtained by adjusting percentage timers in the circurts of the two motors which drove the set point index of the controller. Temperatures were measured with chromel-alumel thermocouples and were recorded by either Brown or Leeds and Northrup 0 to 1000° strip chart recording pote.ntiomet,ers. The thermocouples were calibrated by comparison wlth a standard Pt us. Pt-Rh thermocouple. The recorders were calibrated by frequent comparison with a Leeds and Northrup Type 8662 portable potentiometer which, in turn, had been calibrated against a Rubicon potentiometer standardized by the National Bureau of Standards. The chromel-alumel differential thermocouple shown in Fig. 2 provided a means for detecting liquidus temperntures with greater accuracy than was possible by the use of cooling curves alone. The temperature difference between the two junctions was recorded by either Brown or Leeds and Northrup strip chart recording potentiometers with a full-scale range of 4 mv. Since the chart speeds of these potentiometers were identical with those of the 0-1000" recording potentiometers, the differential temperature record could be superimposed on the cooling curve record for easy companEon. In a typical run, an accurately weighed charge of 15-20 g.
Vol. 63
C. W. BJORKLUND, J. C. REAVIS,J. A. LEARYAND K. A. WALSH
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TABLE XI1 PuClS-LiC1 SYSTEM Mole % PuCla
0
100.0 94.8 83.3 61.9 50.6 39.6 29.5 28.0
60
W 0 500
4
5
0
3
Liquidus, Eutectic, degree degree
767 759 731 670 622 564 479 469
Mole % PuClr
..
17.4 10.3 6.5 4.1 2.7 1.1 1.0 0.0
461 462 462 464 463 461 464
Liquidus, Eutectic, degree degree
530 565 583 595 598 603 604 607
462 461 461 460 459 454 460
..
TABLE IV
1
PuC13-NaC1 SYSTEM 4000
8
24
16
32
40, 48
MOLE
Fig. 3.--PuC4-LiCl I
L
4000
20
*/e
56
64
72
80
88
96
PUGI~.
equilibrium diagram. I
40
I
60
I
BO
Liquidus, Eutectic, degree degree
L
100
equilibrium diagram.
of the fused salt or salts to be studied was added to one of the freezing point tubes shown in Fig. 2. An equivalent amount of LiC1-KC1 eutectic mixture was added to the second tube, or, as was frequently the case, the second tube was replaced by a ceramic crucible which surrounded the lower end of the second thermocouple well. Each tube was evacuated to remove any moisture which might have entered during the loading operation. HC1 was then passed through the tube a t a rate of 40-60 ml./min. as the furnace temperature waa raised through the beating cycle. The gas inlet tube and the thermocouple well were pushed into the salt as soon as it had melted. During each coolillg cycle the HCI flow was continued in order to provide the stirring required to ensure a uniform temperature throughout the melt. The gas was preheated sufficiently in the upper part of the inlet tube a t the flow rate used so that no deleterious cooling effects were encountered. After the desired number of cooling curves had been recorded for a given salt mixture, the composition could be changed by the addition of an accurately weighed pellet of one of the components through a second side-arm (not shown in Fig. 2 ) a t the upper end of the freezing point tube.
Results Equilibrium diagrams for the PuC13-LiCl and PuC13-NaCl systems are plotted in Figs. 3 and 4 from the data in Tables 111 and IV. The melting points of LiCl, NaCl and PuC13 are 607, 802 and 767', respectively. The estimated maximum error in each case is = t 2 O . A eutectic point occurs a t 461' and 28 mole % PuC13 in the PuCL-LiC1 system and at 453' and 36 mole 7PuC13 in the PuC13-NaCl system. All data were based on results obtained from cooling curves.
%Tole % PUCl.3
Liquidiis, Eutectic, degree degree
767 .. 51.0 556 100.0 a 50.2 549 765 97.6 b 49.9 550 761 95.7 48.4 541 92.7 755 47.7 534 89.6 746 446 a 511 43.9 741 87.2 466 37.4 734 450 82.8 485 33.2 715 450 78.7 541 29.2 676 447 70.1 646 21.0 648 451 64.4 704 15.6 624 151 60.3 751 9.8 617 452 59.4 777 5.1 587 449 55.3 792 2.5 54.1 579 448 a 802 0.0 562 51.8 a Salt was not cooled through eutectic region. mal arrest appeared below the liquidus. I ?
MOLE % Pu GI1,
Big. 4.-PuCls-NaCl
Mole % PUClS
(1
452 0
a
453 454 453 a
453 451 450 (I
445 a
.. NO ther-
Discussion The binary systems PuC13-LiC1 and PuClrNaCl are characterized by simple equilibrium diagrams in the temperature range 100-825' with a single eutectic in each system and no evidence of solid solutions. Compound formation was not obseryed in either system. (Indications of an irregularity in the PuCL-rich region of the PuC13-NaC1 diagram were observed, but the evidence was too indefinite for interpretation and was not included in the diagram.) A comparison was made of the melting points of pure LiC1, NaCl and PuC13 after prolonged evacuation a t 0.1 mm. with the melting points of the same compounds in equilibrium with an atmosphere of anhydrous HCl. The results in each case were found to be the same within experimental error. The value 767 f 2' for the melting point of PuC4 was obtained independently by two of the authors using diff ereiit equipment and separate batches of PuC13purified by the hydrochlorinationfiltration technique. The results agreed within one degree. Phipps, Sears, Seifert and Simpsons have reported 760 f 5' as the melting point based on the unpublished work of H. P. Robinson. Their PuC13 was purified by a vacuum sublimation of relatively impure PuC13 prepared by treating dried plutonium hydroxide with CCL at 750-800O. The data in Table 11 indicate that the filtered PuC13 used in the present work contained less than ( 5 ) T. E. Phipps, G. W. Sears, R. L. Seifert and 0. C. Simpson, J . Chem. P h y s . , 18, 713 (1950).
Oct., 1959
VISCOSITYOF AQUEOUSSODIUM FLUORIDE SOLUTION
0.1% total impurities. Moreover, the Pu:C1 ratio of the filtered PuC4 was in excellent agreement with the theoretical value. The melting point of NaCl agreed, within experimental error, with the values 800.4, 801 and 804’ reported in several recent reference^.^-^ A considerable amount of time was devoted to the determination of the melting point of LiCl because of the wide variation in the values reported in the literature. The melting points most commonly quoted, 61307J and 614°,6,8s10 apparently are based on some of the work published between 1910 and 1925.l’ Numerous other values ranging from 600-609° were also reported11~12during (6) N. A. Lange. “Handbook of Chemistry,” 9th ed., Handbook Publishers, Inc., Sandrisky, Ohio, 1956. (7) “Handbook of Chemistry and Physics,” 40th ed., Chemical Rubber Publishing Co., Cleveland, Ohio, 1958. (8) 0. Kubaschewski and E. L. Evans, “lMetallurgica1 Thermochemistry,” John Wiley and Sons, Inc., New York, N. Y., 1956. (9) G. W. C. Kaye and T. H. Laby, “Tables of Physical and Chemir!al Constants,” 11th ed., Longmans, Green and Co., New York, N. Y., 1956. (IO) K. K. Kelley, Bull. U. S. Bur. Mines, No. 393, 1936. (11) R. J. Meyer, “Gmelins Handbuch der Anorganischen Chemie,” 8th ed., Vol. 20, Verlag Chemie, Berlin, Germany, 1027. (12) E. 11. Levin, H.F. McMurdieand B. P. Hal1,“Phase Diagrams for Ceramists,” The American Ceramio Society, Columbus, Ohio, 1956.
1777
this same period. More recent rneas~rements’~-~~ range from 603-610’. The value consistently obtained for all samples of LiCl prepared in the present work was 607’. It was not affected by changing the rate of stirring, the rate of cooling over the range O.P3’/min., or by changing the container from quartz to Pyrex or platinum. The melting point of LiCl under vacuum was the same as that of LiCl in equilibrium with an atmosphere of either dry argon or HC1. It is estimated that a freezing point depression of 6’ (from 613 to 607’) would require a t least 2 wt. yoof an impurity such as NaC1. In view of the analytical data in Table I, it is highly unlikely that such a concentration of impurities could have been present in the LiCl used in this work. Acknowledgments.-The authors are indebted to W. J. Maraman of this Laboratory for many productive discussions and to the members of the analytical group under the direction of C. F. Metz for the analytical data. (13) E. Elchardus and P. Laffitte, BulE. I O C . chirn., 61, 1572 (1932). (14) A. S. Botschwar, 2. anorg. allgem. Chem., SlO, 163 (1933). (15) Metalloy Corp. Minneapolis, Minn., 1944; cf. 12, p. 242. (16) G. A. Bukhalova and A. G. Bergman, Doklady Akad. Nauk, S.S.S.R., 66, 69 (1949). (17) G. Munzhskov, Doklady Akad. Naub, 87, 791 (1952).
VISCOSITY OF AQUEOUS SODIUM FLUORIDE AND SODIUM PERIODATE SOLUTIONS. IONIC ENERGIES AND ENTROPIES OF ACTIVATION FOR VISCOUS FLOW BYE. R. NIGHTINGALE, JR.,AND R. F. BENCK Department of Chemistry, University of Nebraska, Lincoln 8 , Nebraska Received April $8, I969
The viscosities of aqueous sodium fluoride and sodium periodate solutions have been measured in the concentration range 0.0005 to 1 molar. The viscosity data have been interpreted in terms of the Jones-Dole equation for strong electrolytes. Using this relation, the viscosity B-coefficients for the fluoride and periodate ions at 25” are calculated to be +0.0965 and -0.0647, respectively. The energies and entropies of activation for viscous flow at 25” have been calculated for a number of ionic species. Large ions such as Ba+2, ‘103and S01-2, which exhibit a minimal hydration for their reapective charge types, are observed to decrease the activation energy for viscous flow in the solution from that for the pure solvent even t’hough the ion itself increases the bulk viscosity of the solution. The influence of such ions upon the water structure is discussed. Experimental evidence for tshehydration of the 1 0 3 - ion is cited.
Accusate viscosity data for aqueous sodium fluoride solutions and sodium periodate solutions are not available in the literature. The viscosity B-coefficients from the Jones-Dole equation for the viscosity of strong electrolytes have not been reported for any of the fluoride or periodate salts. In conjunction with recent studies in these laboratories concerning the nature and relative sizes of hydrated ions,’ the viscosities of sodium fluoride and sodium periodate solutions have been measured at 25’ in the concentration range 0.0005 to 1 M . These data are interpreted in terms of the Jones-Dole equation, and the viscosity B-coefficients have been determined for the fluoride and periodate ions. The influence of strong electrolytes upon the viscosity of the solvent is interpreted as a rate process, and the energies and entropies of activation for viscous flow have been ( 1 ) E. R . Nightingale, Jr., THISJOURN~L, 63, 1381 (1959).
calculated for a number of salts. From these data the influence of the individual ions upon the energy and entropy of activation for viscous flow has been estimated. The nature of the ion-solvent interaction is considered, and it is demonstrated that for a given charge type, those ions which exhibit a minimal hydration at 25” may decrease the activation energy for viscous flow in the solution even though the ion itself is sufficiently large to increase the viscosity of the solution over that of the pure solvent. Experimental Reagent grade sodium fluoride and sodium metaperiodate were each purified by twice recrystalling the salts from conductivity water. After recrystallization, the salts were dried at 110” for four hours. The salt solutjons were prepared on the molal basis by dissolving weighed quantities of salt into weighed volumes of conductitrity water. The densities of the eolutions were measured a t 25.00 f 0.05’ using
