302
R. G. HIRST, A. J. KINGAND F. A. KANDA
Vol. 60
THE 1 3 A l ~ I U ~ ~ - S T l ~ O N TEQUILIBRIUM IU~~ SYSTEM BY 11. G. HIRST,'A. J. KINGAND F. A. KANDA L'ot&ibulion from the Deparlwienl of Chemistry, Syracuse University, Syracuse, N . Y . Received August 1 1 , 1066
The I)arium-strontium phase diagram has been investigated in the liquid and solid state over the entire range of composit,ions. The liquidus and solidus curves were determined by thermal analysis whereas the solid state equilibria were investigated by X-ray diffraction methods. The system displays complete miscibility in both the liquid and solid states at all temperatures above 602 f 8". Alloys containing less than 69.3 atomic % strontium appear only in the B.C.C. form from room temperature to the melting point. Alloys containing more than 69.3 at. % strontium undergo solid state transformations and may assume B.C.C., H.C.P. or F.C.C. crystalline forms or equilibrium mixtures of these depending upon the % strontium the alloys on cooling undergo the temperature and composition. Between the compositions 72.3 and 76.9:t. eutectoid reaction p (H.C.P.) & y (B.C.C.) and CY (F.C.C.) at 171 =!= 3 The eutectoid composition corresponds to 73.2 at. % strontium.
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Introduction Equilibrium systems of the alkaline earth metals have been an object of research in this Laboratory for several years. Suitable techniques have been developed for handling and obtaining reliable data for these highly reactive metals. Preliminary evidence obtained by Sheldon and King2 using high temperature X-ray techniques, showed that strontium is polymorphic and exists in three crystalline modifications: B.C.C. above 605", H.C.P. from 215-605 and F.C.C. below 215 all i10". Klemm and Mika3found the strontium and barium system at room temperature t o consist of two series of terminal solid solutions. A phase which was F.C.C. appeared between 0 and 24 at. % barium. Another phase, B.C.C. extended from 30 to 100 at. yo barium and the intermediate region consisted of a mixture of these two phases. Rinck4 concluded from electrical resistance, dilatometric and thermoelectric measurements that allotropic transformations of strontium occur a t 235 and 540". Although the temperature of the lower transition is in fair agreement, the higher transition is considerably a t variance with that observed in the present investigation. Sheldon5 investigated the calcium-barium phase diagram by thermal and X-ray methods and found complete miscibility in the liquid and the solid state. He found that calcium can exist in three polymorphic forms with the transitions, F. C. C. + H.C.P. occurring at 335" and H.C.P. + B.C.C. a t 610'. The calcium-rich alloys displayed the eutectoid decomposition: H.C.P. + B.C.C. F.C.C. He also observed thermal evidence for solid state transitions in the calcium-rich alloys which could iiot be verified by X-ray data. Since calcium and strontium exhibit similar polymorphic traiisformations it was expected that the strontium-barium system would be very similar to the calcium-barium system investigated by Sheldoii. Theinvestigation provedthisassumption to be correct. Experimental
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Purity of the Metals and Alloys.-The barium aiid ctrorit,ium were of the highest purity available and were oh--___ ( 1 ) Abstracted froin the thesls of R . G . Hirst submitted to the Clieinistry Dcpartinent of Syracuse University in ],artis1 fulfillment of the rcquirements for the 1'11.D. degree, January, 1953. (2) E. A. Sheldon and A . .I. King, Acta Crysl., 6 , 100 (1Y53). (3) W. Klemrn and G . Mika, Z. a n o i g . albern. Chenh., 248, 155
(1941). (4) E. Kinck, C o m p l . lend., 284, 1845 (1952).
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(5) E. A . Slieldon, Thesia, Syracusc University, 1059.
tuined from King Laboratories, Inc., of Syracuse, N. Y. A gravimetric analysis of their content of barium and strontium showed a purity of 99.3 and 99.5%, respectively. The metals were selected from the middle fractions of 2-3 lb. vacuum sublimed charges. The melting point of the strontium was found to be 768" whereas the melting oint of barium was 714'. Spectrographic analysis showeg the strontium to contain 0.3% barium and traces of Ca, Al, Mn, Sn and Fe. The impurities found in the barium consisted of 0.4% strontium and traces of Ca, Mg and Na. There were minor traces of several other metallic elements in each metal. Alloy samples of approximately 60 g. each were made by weighing, to within 0.01 g., appropriate amounts of the metals in an argon atmosphere. After fusion, a chemical analysis of the samples agreed within f1yoof the make-up composition. The liquidus and solidus curves sloped so slightly that a shift of composition by as much as 2% did not shift the temperature by an amount exceeding the observed accuracy of the temperature measurements. The compositions given in the equilibrium plot correspond to make-up compositions and are reliable to within &l%. Since the metals and alloys used in this investigation react rapidly with ordinary atmospheric gases, special precautions were observed in handling them. Whenever feasible the metals and alloys were handled in a dry box in an atmosphere of purified argon. X-Ray powder specimens were prepared in a unit which allowed for mainterlance of an argon atmosphere during the preparation of the alloy powder and the loading and sealing of the powder into capillary tubes. Studies of the Liquidus-Solidus Equilibrium.-The crucible assembly utilized for this ohase of the investigation consisted of a seamless iron tub;, containing the slmple, fitted into a water-cooled brass head. The brass head was suitably constructed to allow for introduction of the thermocouple and connections for vacuum and argon flushing lines. The thermocouple protection shield consisted of a thin walled iron tube which also served as a stirring device for the alloys. The crucible assembly was alternately evacuated and flushed several times before each run with bariumpurified argon. An argon atmosphere slightly greater than room pressure was maintained in the system during a run by means of a rubber balloon reservoir. Heating and cooling of the wire wound electric furnace was maintained at a rate of 4'/min. by means of a specially constructed program controller which was actuated by a control thermocouple. Thermal data were recorded on a Brown variable range recordera from the output of the recording chromel-alumel thermocouple. The recording thermocouple was calibrated and checked frequently against a standard Pt-90yo P t , 10% Rh thermocouple certified by the National Bureau of Standards. The usual temperature-time curves were adequate for points on the liquidus curve but were unreliable for obtaining reproducible values of points on the solidus curve. Samples were re-investigated using two recorders plotting temperature differential vs. time on one while simultaneously plotting temperature us. time on the other. The 1,cmperature differential was obtained by submerging the charge zone of the crucible in copper powder and recording the difference in temperature between the (6) F. A. Kanda and R. C. Shaver, J . Am. Ceramic Soc., 8 6 , 101 (1953).
Mar., 1956
TABLEI
aSr (F.C.C.) pSr (H.C.P.) ySr (B.C.C.) Ba (B.C.C.)
303
THEB A R I U M ~ T R O N T EQUILIBRIUM IUM SYSTEM This Work
Sheldon and King
uo = 6.076 f 0.005 A. (25') = 4.28 f 0 . 0 2 A. (225') co = 7.05 f 0 . 0 2 A . ao = 4.87 f 0.02 A. (628') uo = 5.013 f 0.005 A. (25')
6.0849 f 0.0005 A. (25") 4.32 f 0.01 A. (248') 7.06 f 0.01 A. 4.87 f 0.01 A. (614') 5.0126' f 0.0001 A. (25')
charge in the crucible and the copper powder. Later in the investigation a two function variable-range recorder was constructed which directly plotted the temperature differential against the temperature. From the temperature differential plots liquidus points could be duplicated to within f1' and solidus points to within f 2 ' in both heating and cooling cycles. None of these techniques were used for obtaining the data for the solid state transformations. Solid State Investigations.-Room temperature and high temperature X-ray diffraction methods were applied in this portion of the study. The Debye-Scherrer type high temperature camera, used in the investigation , was constructed in our laboratory. The entire unit, including the temperature controller and recorder, was calibrated by observing melting points of standardized salt mixtures in capillaries mounted in the camera and by X-ra measurement of the coefficient of expansion of silver. 8 n the basis of these calibrations the reliability of the temperature data is estimated to be within 1 3 ' up to 500', decreasing to f8' at 650". A total of nearly 300 X-ray photographs were taken to establish the points and boundaries in the solid state re ion as shown in Fig. 1. Lattice spacings were determinef by the Straumanis technique. At high temperatures accurate measurement of the lattice spacings was difficult and even impossible for some specimens due to reaction of the alloys with the Vycor capillaries,. grain growth which produced diffraction spots instead of hnes and the diffuse character of lines due to thermal vibration. I n general none of these interfered with the apphcation of the disappearing phase technique which was used as a method of identification of the phases present at the various temperatures. Lattice Dimensions.-The unit cell dimensions of the various lattices observed for the component metals are given in Table I. Also listed for comparison are the data of Sheldon and King.* Nature of the Transitions.-Although the transitions were reversible it was found that they were-usually sluggish. On heating for example, the transition of ( a ) F.C.C. + ( p ) H.C.P. required 4 hours whereas ( p ) H.C.P. -P ( 7 ) B.C.C. required 2 hours at 300' and 30 minutes at 500-600'. On cooling, the transition ( p ) H.C.P. + (a)F.C.C. required eight days for completion at 130'.
Discussion of Experimental Results The two metals form a continuous series of solid solutions (Fig. 1) as would be expected of metals with identical crystal lattices, similar lattice constants and melting points. The solid state region of the strontium-rich alloys is complicated due to the polymorphic character of strontium. The existence of the polymorphic forms of strontium was confirmed and the transition temperatures: B.C.C. -+ H.C.P. (602 f 8') and H.C.P. -+ F.C.C. (213 f 3") found to be in good agreement with the values found by Sheldon.2 The transitions most difficult t o follow in the alloys were those which on heating involved the disappearance of the F.C.C. phase from a mixture of the F.C.C. and H.C.P. phases. This was due to the fact that most of the lines of the F.C.C. pattern were almost superimposed by those of the H.C.P. pattern. The (200) reflection of the F.C.C. pattern was an exception, and was the only one with sufficient intensity to be of use in identifying this phase in the presence of the H.C.P. phase. (7) A. J. King, unpublished result of a precision determination of ao for specially purified barium.
However, its d-value is so close to that of the (111)reflection of SrO that in some instances the presence of the latter rendered the results uncertain. However, with the establishment of the transition temperature of pure strontium and the eutectoid triple point, in addition to two reliable temperature determinations for the disappearance of the F.C.C. lattice, it was felt that enough points were fixed to construct the upper boundary of ths two phase region. The course of the lower boundary line of this region was not so difficult to bracket because the H.C.P. diffraction pattern contains almost twice as many lines as the F.C.C. and its appearance in a two phase mixture was easily recognized.
v
d
500 -
$ 400
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8
-
4
A
300
200 100 I I I I I I *I 0 20 40 60 80 100 Atomic % strontium. Fig. 1.-Temperature us. composition plot of the phase regions of the system. I
I
' i l
I
Three compositions fixed the eutectoid temperature as 171 f 3". The eutectoid reaction: H.C.P. F.C.C. B.C.C. occurs over the composition range 72.3-76.9 atomic yostrontium with the eutectoid composition corresponding to 73.2 atomic % strontium. Since the investigation of the eutectoid boundary regions was made a t 1% (by weight) increments in composition, it is felt that the limits are reliable to within 0.5-1.0%. The limits of the B.C.C.-F.C.C. two phase region a t room temperature were found by application of the parametric method for solid solutions to extend from 69.3-78.0 atomic % strontium. The variation of the uiiit cell parameters with composition ip shown graphically in Figs. 2 and 3. The point of inflection, where the unit cell parameter no longer changes with composition, designates the boundary of a two-phase region. These limits are in good agreemelit with those reported by Klemm and Mika.3 It will be noted in Fig. 2 that by extrapolation a B.C.C. cell parameter of 4.812 A. is indicated for pure strontium a t room temperature although only the F.C.C. form actually exists at this temperature under atmospheric pressure. The atomic radius of B.C.C. strontium calculated
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EMORY E. TOOPS, JR.
30-1
Vol. 60 6.14
, 6.12
1 ’
c:
O S
- 1 0 Fig. 2.-ao
40 60 80 100 Atomic % strontium. values of the B.C.C. (y) phase as a function of composition at room temperature. 20
6.08
from this cell size is 2.083 A. as compared with 2.148 b. for that of the F.C.C. form. This remesents a difference of 3% between the radii of’the atoms in the two structures, a magnitude in good agreement with that predicted for these.8 (8) L. Pauling, “Nature of the Chemical Bond,” Cornell Univ. Press, Ithaca, N. Y.. 1945, p. 406.
6.06
I/
I
0
10
20
30
Atomic % barium.
Fig. 3.-ao values of the F.C.C. (a)phase as a function of composition at room temperature.
PHYSICAL PROPERTIES OF EIGHT HIGH-PURITY NITROPARAFFINS BYEMORY E. TOOPS, JR. Commercial Solvents Corporation, Terre Haute, Indiana Received August 1 1 , 1966
The boiling point, vapor pressure] freezing point, density snd refractive index have been determined for the eight mononitroparaffins from nitromethane through the four isomeric nitrohutanes. The measurements were made on highly purified samples, characterized by both ehullioscopic and cryoscopic methods. The vapor pressure data have been fitted to the Antoine equation by the method of least squares.
Introduction Physical properties of the mononitroparaffins have beeii appearing in the literature during the past 80 years. Few reliable data are available, with the exceptioii of nitromethane, whose properties were carefully measured by Timmermaiis and Heiiiinut-Rolatid.‘ Measurements made during the past 20 years are particularly liable to error because commercial products have been used without adequate purifiaatioii. Nitromethalie, iiitroethaiie and 1- and 2-nitropropatie are made coniincrctially by the vapor phase iiitratioii of propane.' These materials are available coiitaiiiiiig 90-957, w. of the spccificd product with a total iiitroparaffiri coiiteiit of at least 99%. A carcfiil fractioiial distillation is essential to obtain a high purity tiitroparaffiii. A suiiimary of physical data 011 these conipouiids reeeiitly has been p uklishcd . 3 Wlict icver possil)lc the iiitropnrsfFiiis wore prepared by syiithesis as well as I,y purifying the conirnervial product. The primary iiitropareffins can be prepared i n good yields from the corresponding ( 1 ) J. Tiiiiinerinnns and hI. Hennant-Roland, J . chim. phus., 29, 524 (1932). ( 2 ) C. I,. Cahriol. I n d . E w . C h e m . 32, 887 (19.10); S. 1). Kirkustrick. Chem. d Aid. E n g . , 4 4 IO]. 124 (1943). (3) A. Weissbcrrcr, ” T e c l i n i ~ l ~ iofe Orgnnic C h e n i s t r y , ” Vol. V I I , Interscience Publisliera. New York, N . Y., 1955.
Inc..
alkyl bromide or iodide by the Victor Meyer react i ~ n . They ~ may also be prepared in satisfactory yields from the corresponding a-halogenated acid by the Kolbe s y n t h e ~ i s . ~This method is an excelleiit laboratory preparation of nitromethane from chloroacetic acid.6 AI1 purifications of both the synthetic and commercial nitroparaffins were made by careful fractional distillation, except for nitromethane where both fractional distillation and fractional crystallization were used. The products were collected in 100-ml. fractions during the distillation and preliminary purity measurements made by mass spectra analysis. Preparation and Purification of the Nitroparaffins Nitromethane was prepared from the commercial product by fructional distillation in a Podhielniak Hyer-CuI column a t 100 mm. prennurc, followed hv a fractional crystallizatiori in which one-half of thc sample was disc:irtlrd as mother liquor. A inntcthl of cqriiv;dent purity was prepared from c4iloro:tcct.io acid and sodium Iiitritc. ( 4 ) V. h h y e r , Ber., 6 , 203, 399, 514, 1029, 1034 (1872); N. Kornbluiii. N . Lichtin, el ol., J. ,477~. Chem. SOC.,6 9 , 307 (1947); N. [cornbluiii. J. T. I’atton and J. B . Nordinann. ibid.. TO, 746 (1948); C. W. Pliiiniiier and N. L. Drake. ibiu.. 7 6 , 2720 (1904). ( 5 ) 11. I
