BARIUM-SODIUM EQUILIBRIUM SYSTEM
3867
The Barium-Sodium Equilibrium System’
by F. A. Kanda, R. M. Stevens, and D. V. Keller Chemistry Department, Syracuse University, Syracuse, New York (Received M a y 88, 1966)
The barium-sodium phase system has been investigated in the solid and liquid state over the entire range of compositions. The liquidus and solidus curves were determined by thermal analysis methods, whereas the solid-state equilibria were studied by X-ray diffraction methods. This system displays complete miscibility in the liquid state. The solid wiubility of sodium in barium and barium in sodium is 3 and 0.5 atomic %, respectively, at room temperature. The system has two compounds: BaNa4, which is formed through a peritectoid solid-state reaction at 65O, and BaNa, which melts incongruently at 197’. Sodium is appreciably soluble in BaNa; barium is not. A eutectic, which melts at 82O, forms at 5.5 atomic % barium. X-Ray diffraction patterns have indicated BaNa4 to be tetragonal with cell dimensi2ns a0 = bo 9.19 8. and CG = 17.20 8. and all *0.02 8. BaXa to be orthorhombic with a0 = 4.24 A., bo = 5.86 A., and co = 9.63 i., The sodium metal used had a melting point of 97.5’ andD@= 4.283 f 0.003 8. at 22’. The barium melted at 729’ and had a0 = 5.026 f 0.003 A. at 22’. A comparison of the results of this investigation with other data obtained for this system is presented.
Introduction The barium-sodium system was investigated in this laboratory as part of an over-all program to study the alloying behavior and characteristics of the alkaline earth metals. Several equilibrium systems involving the alkaline earth metals, e . g . , Ba-Sr,2 Ba-Li,3 Ca-Sr,4 Sr-Li,S and Sr-Na6 studied previously or concurrently have lead to techniques which allow for the accurate and reliable delineation of phase boundaries in these systems. At the onset of this present investigation, no complete study of the phase relationships within the barium-sodium system had been reported. Gould’ and Miller* independently investigated the solubility of barium in sodium and reported conflicting results. During the course of this investigation Remy, et U Z . , ~ published the results of their investigations of the barium-sodium equilibrium system. However, it was decided to complete the study of the system in this laboratory since the results of the two independent investigations over the same composition ranges were considerably different. Also, the barium used by Remy, et al., was obviously quite impure (map.710°), and their differential thermal and time-temperature thermal results were inconsistent.
Experimental Section The sodium used in this study was obtained from the Baker and Adamson Chemical Co. This metal gave cooling curves which displayed ideal flat plateaus at the melting point. These isothermal arrests corresponded to a melting point of 97.5 f 0.2’. Barium was furnished by King Laboratories Inc., Syracuse, N. Y. It was purified before use by fractional distillation in a high-temperature stainless steel bomb (1) Abstracted from the dissertation of R. M. Stevens submitted t o the Chemistry Department of Syracuse University in partial fulfillment of the requirements for the Ph.D. Degree, June 1964. (2) R. G. Hirst, A. J. King, and F. A. Kanda, J. Phys. Chem., 60, 302 (1956). (3) D . V. Keller, F. A. Kanda, and A. J. King, ibid., 62, 732 (1958). (4) J. C. Schottmiller, A. J. King, and F. A. Kanda, ibid., 62, 1446 (1958). (5) F. E. Wane, F. A. Kanda, and A. J. King, ibid., 66, 2138, 2142 (1962). (6) W. 0. Roberts, Ph.D. Dissertation, Syracuse University, 1964. (7) J. R. Gould, Knolls Atomic Power Laboratory, Schenectady, N . Y., KAPL 1398, 1955. (8) R. R. Miller, private communication, reported in “Liquid Metals Handbook, Na-K Supplement,” 3d Ed., U. S. Government Printing Office, Washington, D. C., 1955. (9) H. Remy, G.Wolfrum, and H. W. Haase, Schweiz. Arch. angew. Wise. Techn., 26, 5 (1960).
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November 1966
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mm. a t 900'. capable of holding pressures of After condensation of the distillate on the water-cooled cold finger in the distillation bomb, the porous condensate was melted off in situ in an argon atmosphere and collected as a cast ingot in a container below the cold finger. This technique avoided the exposure of the barium to the atmosphere until after it was cast, minimizing contamination by nitrogen, an effective depressant of the melting point.'O As a consequence, only the top of the smooth surface of the ingot was subjected to atmospheric exposure and contamination during transfer of the charge from the bomb to the drybox. This proved important since noncast condensates are exceedingly porous and become extensively contaminated when exposed to the atmosphere, even for a short time interval. The latter porous material is also difficult or impossible to scrape clean of surface contaminants, such as barium nitride, when preparing alloys. Spectrographic analysis of the bright refined barium showed it to contain 0.07% Sr, 0.03% Ca, 0.01% Na, and traces of Mg, K, and Li. The melting point, 729 =k l o , was obtained as an essentially ideal flat plateau on a time-temperature cooling curve. This is in agreement with the highest melting point reported previously. l1 The authors also noted that barium purified in this manner displayed a softness approaching that of sodium. Alloys were prepared by weighing the appropriate amounts of metals to within 0.001 g. in a drybox in which a purified argon atmosphere was maintained. The alloy samples, ca. 10 ml. in volume, were loaded and stoppered under argon in thin-walled, low-carbon steel tube crucibles approximately 2.54 cm. in diameter and 30.48 cm. long, These were ultimately transferred from the drybox to the thermal analysis unit and continually maintained under an argon atmosphere. The basic equipment and techniques employed for the thermal analyses of the alloys have been described previo~sly.2-~The thermal analysis furnace was provided with water and forced-air cooling features to allow for program-controlled linear cooling rates of 0.8'/min. in the lower thermal ranges of investigation, e.g., 50-125'. Cooling rates between 0.8 and 2.0°/ min. were used in the higher thermal ranges with the slower rates usually preferred. The chromel-alumel thermocouples used in the thermal analysis were periodically checked against an N.B.S. certified standard thermocouple, and the temperatures reported in the phase diagram are considered reliable to within a t least h2O. Both timetemperature and differential temperature-time curves were obtained simultaneously for all alloys. Alloys were investigated in the solid state by X-ray The Journal of Physical Chemistry
F. A. KANDA,R. M. STEVENS, AND D. V. KELLER
powder diffraction methods. Several alloys were also studied in the range 25-200' using either a hightemperature X-ray powder camera or a high-temperature atmosphere-controlled X-ray diff ractometer. XRay specimens in the 0-20 atomic % barium range were prepared as fine slivers shaved from alloy slugs. Alloys above 20 atomic yo barium content were sufficiently hard to be filed and, consequently, were prepared as fine filings. All X-ray samples were prepared in a drybox.
Results The results of the thermal and X-ray studies of the barium-sodium system are shown in Figures 1 and 2. A total of 47 different alloy compositions was ultimately investigated. One eutectic is present, and this occurs at 5.5 atomic % barium. The eutectic temperature is 82'. Millers reported two eutectics at barium contents of 2.9 atomic % (85') and 8.3 atomic % (82'), while Remy, et aL19reported four at 5.6 atomic % ( 8 5 O ) , 12 atomic % (78'), 26 atomic % (57.2'), and 70 atomic % barium (180'). Yo congruent-melting compounds were indicated by thermal analysis in this investigation. On the basis of thermal analysis, Miller's results indicate a congruent-melting compound of the approximate composition BaNa24, and Remy, et al., report BaNalz and BaNa6 in the 0-20 atomic % barium range of the phase diagram. No reference is made to the use of Xray techniques in order to validate the existence of these compounds in either investigation. X-Ray results of the present investigation prove that no compounds of such compositions exist. All diffraction patterns displayed a mixture of a-sodium diffraction lines with the lines of BaNar. No other diffraction lines occur for specimens within the 0-20 atomic % barium composition range when the samples are properly equilibrated. Cooling curves for alloys between 2.5 and 25 atomic % barium produced an additional isothermal pause following the eutectic solidification. This pause, which occurred a t 65 =t 5', was due to the solid-state peritectoid reaction: a y + BaNa4. This reaction was studied in the high-temperature X-ray diffractometer in both heating and cooling directions. Thus, BaNaa was found to decompose readily into a! and y solid solutions when heated at 70'. Specimens rapidly quenched from 70' displayed only a and y
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(10) V. A. Russell, M.S. Thesis, Syracuse University, 1949. (11) D.T. Peterson and J. A. Hinkebein, J . Phys. Chem., 63, 1360 (1959).
BARIUM-SODIUM EQUILIBRIUM SYSTEM
3869
800
700
600
500
P w 0
2 xf
400
2 300
200
100
Figure 1, The barium-sodium equilibrium system.
diffraction patterns, but, in contrast, when these were slowly cooled through the peritectoid temperature, the lines of BaNar readily appeared. During solidification of the y intermediate phase from the melts of alloys in the range 5-23 atomic % barium, drastic cases of segregation occurred. The y phase has a density approximately twice that of the melt from which it separates. As a consequence, it would readily settle to the bottom of the crucible resulting ultimately in an incomplete peritectoid reaction with the a solid solution. Thus, X-ray specimens selected from the bottom portions of the crucibles displayed only y diffraction lines whereas specimens from the top portions of the charge showed a and BaNar lines. While these conditions pertained, the stoichiometry of the compound could not be ascertained. Small alloy specimens, ca. 1-2 ml. in volume, were prepared and cold-worked for 1-2 hr. in the jaws of a vise in the drybox. This continual
kneading physically homogenized the alloys. After annealing the alloys, X-ray patterns showed the asodium lines to occur only in samples with less than 20 atomic % barium content at room temperature. The y diffraction pattern only appeared in samples above 20 atomic % barium and existed exclusively in all samples between 21-50 atomic % barium when X-rayed at room temperature. As a consequence, it was deduced that the compound whose diffraction pattern appeared with both a and y had the composition BaNa4 which crystallized in a tetragonal cell (Table I). This investigation found some alloys containing as high as 45 atomic % barium produced the eutectic pause a t 82' owing to nonequilibration of the peritectic reaction. This pause was readily eliminated by soaking the sample for a few hours below the peritectic temperature. Alloys of 28 and 30 atomic % barium content were soaked for as long as 6 weeks at 100' in order Volume 69, Number 11 Nonember 1966
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F. A. KANDA,R. M. STEVENS, AND D. V. KELLER
300
200
v 2.
+
2
i
G
100
0
10
20 Atomic % barium.
30
40
50
Figure 2. The sodium-rich end of the barium-sodium system.
to eliminate the eutectic pause. Thus, as a consequence of lengthy equilibration, it has been established that the eutectic horizontal does not extend beyond 28 atomic % barium. It is possible, in view of these findings, that equilibration over still longer time periods may prove this limit to be less than the 27 atomic % value shown in the diagram. The sloping boundary of the y region between 27 atomic % at 82' and 21 atomic % barium at room temperature is dotted in order to indicate some uncertainty in both its composition limits and curvature due to the equilibration difficulties discussed above. Miller's works was concerned with the determination of the liquidus over a limited range of compositions. The results are substantially in accord with those of this investigation. In most cases, the variation of liquidus points is of the order of 3'. The existence of BaNa has been previously reportedg; however, it was reported as being a compound with a congruent melting point of 510'. On the basis of extensive thermal analysis investigations of several separate alloys of this composition, no solid The Journal of Physical Chemktry
phase was found to form until the liquidus temperature of 315' was reached in conformity with Figures 1 and 2. Furthermore, reinvestigations of alloys covering the 40-60 atomic % barium range showed no evidence whatsoever of a congruent melting point dome but rather a continually rising liquidus boundary. ' barium alloy, when soaked at Finally, a 40 atomic % 210' and then rapidly quenched, clearly showed the presence of p-barium diffraction lines. The sluggish peritectic reaction was of aid here to allow the retention of the p phase. If there were a compound possessing a congruent melting point as postulated by Remy, et al., the region in which the 40 atomic % ' barium alloy was soaked as described above, would have to be a phase region consisting of BaNa and liquid, and there would be no conceivable way for the ,&barium to occur in the sample. A similar 40 atomic yo barium alloy, when soaked and quenched from 175', no longer showed the presence of p-barium but, instead, showed only the y phase, indicating the peritectic reaction, p liquid -t y (197O), had occurred. Room-temperature X-ray patterns indicated the
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BARIUM~ODIUM EQUILIBRIUM SYSTEM
3871
Table II: X-Ray Data for the Compound BaNa; a0 = 4.26 R.; bo = 5.88 R.; co = 9.65 A., aU. ~ 0 . 0 2 R.
Table I: X-Ray Data for the Compound BaNad; a0 = bo = 9.16 A 0.03 R.; co = 17.28 f 0.03 A. Line no.
Sin 8
d
hkl
Line no.
Sin 0
d
hkl
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
0.083 0.092 0.118 0,125 0.134 0.173 0.205 0.229 0.241 0.251 0.305 0.313 0.325 0.339 0,357 0.368 0.379 0.388 0.398 0.414 0,421 0,437 0.449 0.471 0,506 0,536 0,565
9.23 8.46 6.51 6.18 5.76 4.44 3.76 3.36 3.19 3.06 2.53 2.46 2.37 2.27 2.16 2.09 2.03 1.98 1.93 1.86 1.83 1.76 1.72 1.63 1.52 1.44 1.36
100 002 110 102 003 201 (004) 104 123 105 300 304 (230) 232 (007) 206 305 008 (330) 108 333 (404) 235 334 119 500 245 250 505 601 450 361
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
0.080 0.132 0.182 0,198 0.223 0,235 0.257 0.286 0,323 0.347 0,371 0.385 0.392 0.424 0,451 0.460 0,468 0.494 0,527 0.533 0.542 0,548 0.559 0.591 0.605
9.65 5.85 4.24 3.89 3.46 3.27 2.99 2.69 2.39 2.22 2.08 2.00 1.96 1.81 1.71 1.67 1.64 1.56 1.46 1.45 1.42 1.40 1.38 1.30 1.27
001 010 100 101 110 111(003) 020 021 120 (004) 023 201 210 030 032 220 033 132 133 041 230 300 232 007 107 044
alloys ranging from 51 to 97 atomic % barium consisted of y (BaNa) and P-barium with the y diffraction lines becoming progressively weaker as alloys approached 97 atomic % barium. The powder pattern of BaNa has been indexed on the basis of an orthorhombic cell. The d values and indices are given in Table 11. The y-solidus boundary, above 82', could not be determined reliably by direct thermal analysis methods since this boundary represents completion of solidification accompanied by a changing composition of the solid phase. As pointed out above, equilibration in this region was very difficult to realize, necessitating prolonged soaking periods in order to allow for appropriate diffusion and consequent adjustment of the y composition. For this reason, only a selected set of samples was prepared and cold-worked in the vise, homogenized, and soaked a t 100' for several weeks for this part of the investigation. Diffractometer samples of these were then investigated at successively higher temperatures with a 2-hr. soak given at each temperature investigated. As the solidus was approached, the X-ray pattern became continuously more diffuse, but only showed the y pattern. Simul-
taneously, while soaking, the sample could be observed in the camera furnace through a Mylar window. It was observed that, when the X-ray pattern displayed no evidence of crystallinity, beads of liquid appeared on the surface of t,he specimen. This temperature was plotted for each sample investigated to delineate the solidus boundary as shown in Figures 1 and 2. This boundary probably represents an upper limit for the initial melting of y. It is conceivable that intermediate regions of the boundary between 82 and 197' may be as much as 10' lower than that shown. The eutectic reported by Remy, et at NO', with an erratic spread of temperature, is apparently the isothermal peritectic pause at 197'. It was found in the present investigation that this pause could be suppressed to as low as 180' by supercooling. However, if slow cooling rates and vigorous stirring were employed, this isothermal appeared consistently at 197 f 2'. Thermal analysis and X-ray powder patterns proved the solidus and solvus of the terminal solid solutions CY and P to be as shown in Figures 1 and 2. Application of Vegard's 1av@ to a series of room-temperature (12) L. Vegard and H. Dale, 2.Krist., 67, 148 (1928).
Volume 69,Number 11
November 1966
3872
MICHAELE. LAMMAND DAVIDM. NEVILLE,JR.
films provided the room-temperature points on the solvus. The solubility of barium in sodium is of the order 0.5 atomic % barium at room temperature and a maximum solubility of 3 atomic % at 6 5 O , the peritecOoid temperature. The solubility of sodium in barium was found to be 3 atomic % sodium at room tempera-
ture and a maximum solubility of 5 atomic % a t 197O the peritectic temperature.
Acknowledgment. The authors wish to express their gratitude to the Atomic Energy Commission for the financial support which made this study possible.
The Dimer Spectrum of Acridine Orange Hydrochloride
by Michael E. Lamm* and David M. Neville, Jr. Laboratory of Neurochemistry, National Institute of Mental Health, Bethesda, Maryland (Received M a y 88, 1966)
The absorption spectra of the cationic dye acridine orange hydrochloride have been deterM . Over this range mined at eight different concentrations in water from loP6to the spectra change continuously. An isosbestic point is observed at 470 mk. The spectral data are interpreted in terms of monomer-dimer equilibria. Agreement of the data with two different equilibria has been checked by means of a computer program employing a reiterative procedure which varies the equilibrium association constant, K , as an arbitrary parameter until a value of K is found which gives the smallest root-mean-square deviation of the optical density data with the equilibrium model. The two models, (1) involving dye cations only, 2D+ = Dz2+,and (2) anions as well, 2D+ A- = D2A+, fit the data equally well with K = 1.05 X lo4 I. mole-' and K = 4.7 X lo8 respectively. Dimer spectra obtained by extrapolating the data with the above models differ. Dimer spectrum 1 shows a symmetric splitting in relation to the monomer peak while dimer spectrum 2 exhibits a redistribution of intensity between the monomer peak band and shoulder band. The significance of the dimer spectrum in relation to current theories of metachromasy is discussed.
+
Introduction The pronounced effect of concentration on the color of aqueous cationic dye solutions has been known for over 50 years. Various physical descriptions of this phenomenon have been proposed, yet to date the superiority of any one model remains to be demonstrated. The spectral changes are known to be associated with reversibIe poIymerization of dye, and at low concentrations the predominant aggregate species is believed to be a dimer.2 A knowledge of the absorption spectrum of the dimer is crucial to the understanding of the physical process involved in the spectral The JOUTTMZ~ of Physical Chemistry
changes. Unfortunately, the dimer never exists alone and its spectrum is obscured by contributions from monomers and higher aggregates. To date, the dimer spectra of at least four different dyes have been derived utilizing certain critical assumptions.a-6 In each case the reaction has followed the scheme ~
*Department of Pathology, New York University School of Medicine, New York, N. Y. (1) S. E.Sheppard, Proc. Roy. SOC.(London),A82, 250 (1909). (2) V. Zanker, 2.phg8ik. Chem., 199, 226 (1952).
