June, 1958
VOLUME CHANGE O F
INDIUM
meta to a methoxy group is slightly activated for electrophilic bromination of anisole in acetic acid and that the methoxy group activates the meta position slightly less than does the methyl. In view of this, it appears that the a-value may be in error and that the correct value would be in good agreement with the spectroscopic data. p-Nitrosopheno1.-The 0-H stretching frequency of 3563 cm.-l found for p-nitrosophenol is much lower than that obtained for any other phenol, so low in fact that it is close t o the region normally associated with the N-H frequency. This is quite incompatible with the U-value of 0.123 found by Betti" and does not fit any type of a*-value which can be reasonably postulated. Upon extrapolating the curve in Fig. 2 to a frequency of 3563 em.-', an impossibly large a*-value of 3.49 is calculated for the nitroso group. A logical explanation of this problem is that in dilute CCl, solutions the most stable structure for p-nitrosophenol is the quinoid 111, rather than the phenolic IV form. 0
OH
0 I
NOH I11
NO IV
The 0-H band is due, therefore, to the hydroxyl group of the oxime and is more compatible with the 0-H frequency and acidity of conjugated oximes rather than with substituted phenols. This result is confirmed by Jaffe's12 molecular orbital calculations which predict that I11 is the stable structure. The resonance energy of stabilization for structure I11is obviously greater than that for structure IV; this is, a t first sight, somewhat surprising. Dipole Moments.-In studies of dipole moments of the nitro group, it is generally considered that inductive and resonance effects can be distinguished by forcing the nitro group out of the aromatic plane by ortho substituents. At large angles, resonance interaction between the two groups is almost completely suppressed. A representative example is 4-nitro-3,5-xylenol which has an 0-H frequency (11) M. Betti, T r a n s . Faraday Soc., 26, 337 (1030). (12) H. 11. Jaffe, J. Am. Chem. Soc., 77, 4448 (1955).
ANTIMONIDE DURING FUSION
747
of 3595.5 em.-', 10.5 em.-' higher than that of p-nitrophenol and 2.5 cm.-l higher than that of m-nitrophenol. The methyl group is not large but the presence of one in each ortho position is sufficient to rotate the nitro group out of the aromatic plane. If the increase in frequency is due only to a reduction in resonance, the electron withdrawing power due to resonance is considerably greater than that calculated from a-values and is large even for the meta position. However, the methyl groups make a substantial Contribution to the electron density at the common ortho position, and this reduces the ability of the nitro group to lower the electron density at the para position. Experimental confirmation to this is given by the fact that the 0-H frequency of o-cresol is higher than that of p-cresol by 1-2 cm.-l. The steric interaction between the 0-H and CH3 groups is probably so slight that it does not measurably affect the 0-H force constant by bond deformation and rehybridization. Consequently, the methyl group is donating electrons to both the ortho and para positions, but slightly more to the ortho than to the para. As a result no conclusions are justified concerning the exact contributions of resonance and inductance of a nitro group from either these data or those of dipole moments without extension to additional groups which would permit the electron donating powers of the methyl groups to be evaluated q~antitative1y.l~ Second-order Effects on the 0-HForce Constant One of the factors which might be affecting the 0-H frequency, in addition to the electron density at the adjacent carbon, is the state of bond hybridization. The resonance interaction of the type drawn above for phenols increases the amount of s character in the sigma bonds around the oxygen and might, therefore, tend to increase the force constant. Since resonance interaction decreases as the electron density increases (decreasing a), the amount of s character decreases and the force constant should increase to a smaller extent than expected from a consideration of only the electron density. This is, at most, a second-order effect and if detectable a t all, should merely cause a slight curvature in the plot of Fig. 2. However, within the limits of experimental accuracy, no curvature is detected. (13) G. W. Wheland, R. M. Broivnell and E. C. Mayo, zbid., 70. 2492 (1948).
VOLUME CHANGE OF INDIUM ANTIMONIDE DURING FUSION BY NORMAN H. NACHTRIEB AND NORIKO CLEMENT Institute for the Study of Metals, University of Chicago, Chicago,Illinois Received February 84, 1968
The change in volume of indium antimonide on fusion haR been determined from measurements of the change in pressure of argon at constant volume. The average of six determinations gives 100 AV/V, = -13.7 f 0.5%, referred to the solid.
Comparatively few measurements have been reported for the volume changes attending melting of the Group IV semiconducting elements and for the Group 11-VI and 111-V intermetallic com-
pounds, although it is well known that many of them contract. Like ice, bismuth, gallium and antimony, some of these substances are more densely packed in their liquid state. An accurate
748
NORMAN H. NACHTRIEB AND NORIKO CLEMENT
Vol. 62
for germanium, with an electrical probe to contact the meniscus in a capillary stem. Their results varied from -4.0 to -6.3%, with -5.4 f 0.4% as the most probable average, referred to the solid. Difficulties with gas evolution and impurityfouling of the meniscus were encountered. Mokrovskii and Regal6 appear to have made a careful study by observing the meniscus in a narrow bore quartz tube with a traveling microscope. They found -5.08% referred to the solid for germanium, -7.0% for GaSb, and -11.4% for InSb.
Experimental
Fig. 1.-Schematic
drawing of apparatus.
determination of the change in their volume during fusion is of importance for considerations of the theory of melting. The precision of measurements of this property is generally low, although three or four different methods have been employed. The present study reports the results obtained for the substance InSb, by a method which does not appear t o have been adapted t o this purpose heretofore. It was undertaken in order t o permit evaluation of the change in melting temperature with pressure from the Clausius-Clapeyron equation, and also because there appeared to be unaccountably large differences in the volume contraction for germanium, silicon and indium antimonide from reported studies. The elements have the diamond (A,) structure, while InSb and most other 111-V and 11-VI intermetallic compounds have the closely similar zinc blende structure (B3) in the solid state. Both structures have tetrahedral coordination. Von Wartenberg1 weighed the material extruded during the freezing of a given mass of silicon and reported -10 f 1% for the volume change. Klemm, et u E . , ~ applied von Wartenberg's method to germanium, and concluded that it gave somewhat low results (-4.970, as compared with -5.5 f O.5Y0from two other methods). Using Nitka's value for the lattice constant3 extrapolated to the melting point together with their data for the liquid density, they calculated -6.4% as the volume change referred t o the solid state. In a third method they used a quartz pycnometer containing liquid NaCl above the germanium, and noted the meniscus drop in a graduated stem on freezing the germanium. The results varied from -4.3 to -6.l%, the two most reliable being -5.3 and - 5.4%. Sangster and Carman4used a pycnometer method (1) M.von Wartenberg, Nuturwiss., 36, 373 (1949). (2) W. Klemm, H. Spiteer, W. Lingenberg and H. J. Junker, Monulsh. Chem., 83, 629 (1952). (3) H. Nitka. Physik. Z., 38, 896 (1937). (4) R. C. Sangater and J. N. Carman, Jr., J . Chem. Phua., 23, 206 (1955).
The method devised in the current study consisted in determining the change in volume of the substance during fusion from the change in pressure of an inert gas above it with a constant-volume manometer. It is free of some of the difficulties encountered in the foregoing methods although, as will be seen, some results were low because of the release of gases dissolved in the indium antimonide and had to be discarded. Figure 1 shows the essential details of the system. A is a bulb of quartz or Vycor (33 to 48 cm.S capacity) terminating in a long capillary (0.5 mm. dia.) and attached to the system by a ball and socket joint. The bulb was centrally situated in a Nichrome wound furnace (9.5" long) with vermiculite insulation above and below it in the steel liner. A chromel-alumel thermocouple between the bulb and the liner was used for measuring the specimen temperature with a Rubicon Type potentiometer. Four chromel-alumel thermocouples in series (not shown) close to the furnace winding were used for controlling the furnace temperature with a Leeds and Northrup recording-controlling potentiometer. B is a bulb of 111.9 cm.8 capacity used for calibrating the volume of the system. C is the constant volume manometer, constructed from 16 mm. i.d. Pyrex tubing, and connected to the manifold of a high vacuum line. A cobalt glass indicating needle inside the manometer at D was used to set the level of the mercury meniscus in the Rhort limb. The difference in the heights of the mercury levels in the manometer was measured with a cathetometer. Calibration of the gas-accessible volume of the system above the compound was accomplished by admitting argon to the system including the calibration bulb and measuring the pressure. The calibration bulb was then closed off and the system was evacuated to 10-6 mm. through stopcock E. Stopcock E was then closed and the gas in the calibration bulb was expanded into the system and the pressure remeasured. Argon gas, purified from oxygen by passage through a heated column of finely divided copper on diatomaceous earth,E was admitted to the quartz bulb at a pressure of 10 to 25 cm. and accurately measured. Pressure measurements were made a t a series of furnace temperatures up to about 700'. In general, about one hour was required for temperature equilibrium to be established a t each temperature. Frequently the temperature of the furnace was lowered to check the possibility of leaks in the system and t? determine the times required to attain thermal equilibrium. It was not generally possibIe to retrace the measurements once the indium antimonide had melted (map. 525") because the quartz bulb usually broke under the stresses set up by expansion during solidification. Figure 2 shows the variation of pressure with temperature for a typical good run. Unexpected difficulties were encountered in the first two runs, which were traced to the release of a gas during melting of the indium antimonide. The gas was presumably hydrogen, which had been employed in the zone-refining of the compound. When recognized, the trouble was eliminated by vacuum melting in the quartz tube prior to its attachment to the manometer system. To prevent breakage of the quartz tube it was necessary to solidify the liquid from the bottom upward by partial immersion of the bulb in a water-bath. The density of indium antimonide was determined by (5) H.P. Mokrovskii and A. R. Repel. J . Technical Phys., 22, 1282 (1952). (6) F. R. Meyer and G. Ronge, 2. angew. Chem., 62, 637 (1939).
t
.
June, 1958
VOLUMECHANGE OF INDIUM ANTIMONIDE DURING FUSION
conventional means ?t 25” and found to be 5.780 g./cm.*, in good agreement with the value of 5.783 g./cm.8 as calculated from Liu and Peretti’s’ recise measurement of the lattice constant (a, = 6.4760 A.Y. The indium antimonide used waa n-type, of quality sufficiently pure for thermodynamic measurements, but not of high quality from the standpoint of its electronic properties. Analysis for antimony gave 51.44 f 0.16~0,as compared with the theoretical value of 51.48% for the composition InSb. Semi-quantitative spectrographic analysis revealed Fe (0.001%), Pb (0.001%), Sn (0.001%), Mg (0.001%1), Si (0.0001%), and c u (0.0001%).
v
626’
Calculations and Results Since the gas temperature varied from room temperature in the manometer up to the temperature of the furnace, the system was not in true thermal equilibrium throughout. A suitable approximation was made, however, by treating the system as consisting of two sub-systems with a common pressure and different, but separately uniform temperatures. The approximation was valid in the present case because the temperature gradient lay wholly within the negligibly small volume of the capillary connecting the quartz bulb with the manometer. Moreover, the capillary radius was small, so that convection currents within it were unimportant. Let the volume of gas above the solid indium antimonide at its m e l h g temperature T , be VZ, and let the volume of gas outside the furnace be VI at room temperature, To. Further, let the pressure in the system a t the melting point of the compound be P, above the solid and P1 above the liquid. The volume change of the compound on fusion is designated by -AV. Then it is readily seen from the ideal gas law that This equation neglects the expansion of the quartz bulb and the indium antimonide, both of which separately lie within the experimental error and tend to cancel one another. For each run the total gas volume (VI 4- V,) was obtained a t room temperature by expanding gas into the evacuated system from the calibration bulb. The volume Vl was measured in the same manner after a run was completed by sealing off the quartz capillary a t the point where it emerged from the furnace, and V 2 was obtained by difference. A check of the accuracy of this determination and a validation of the aforementioned approximations was provided by the (P,T) data of each run. It is shown readily that up to the melting point of the compound
749
I
I
I
I 200
0
I
400
TEMPERATURE
Fig. 2.-Pressure
I
I BOO
600 (*C.j.
vs. temperature (run V).
1 -
0
.
.02
.O 4 P
Fig. 3.-Determination
I
(7,
.06 t
.08
-
of
“1
(run V).
melting the InSb was not appreciated at that time. Discussion An accurate theoretical accounting of the magniwhere T0”and Po are the initial temperature and tude of the various factors which enter into the pressure, and T1and P are the subsequent room change in volume of fusion is not yet generally postemperatures and system pressures; TZis the tem- sible, although considerable success has been perature of the gas in the furnace region. A plot had with argon.8 I n the intermetallic compounds, V,) (Po/To- P/Tz) yields VI as the slope to an even greater extent than in metals and ionic of (VI (Fig. 3). The volume VI was usually about 5 cm.a, salts, the phenomenon is complex. Apart from and the agreement between the two methods was the still imperfect knowledge of the structure of within 1%. Table I summarizes the results ob- liquids, there are two additional effects which tained for all runs. The values obtained for runs enter when substances having spa bonding melt: 1 and 2 are low because the necessity for vacuum (1) the large increase in coordination number, and
+
(7)
T.S. Liu and E. A. Peretti, Trans. J . Metals, 8, 791 (1951).
( 8 ) F. Sauerwald, 2. MetaEEk., 41, 07 (1950).
NOTES
750
Vol. 62
TABLE I VOLUMECHANGE O N FUSION OF INDIUM ANTIMONIDE Wt. InSb, Run
I" 11" I11 IV V VI VI1 VI11
TO (OK.)
g.
VS
(vacuo)
(cm.8)
(cm.)
(cm.)
(om.*)
VZ (cm.8)
(cm.3)
- 100 A X vs
297 297 297 298 298 298 30 I 303
224.26 246.88 234.49 183.44 172.65 147.93 131.57 158.72
38.80 42.71 40.57 31.74 29.87 25.59 22.76 27.46
14.640 18.270 25.600 45.560 45.800 42.080 50.180 56.040
12.460 15.200 10.920 39.160 40.000 36.720 43.880 49.260
7.40 7.40 4.68 4.95 5.08 4.63 4.82 4.93
5.95 5.36 6.02 13.21 13.11 12.75 10.14 12.82
4.54 5.12 5.56 4.33 3.88 3.67 3.30 3.55
11.7 12.0 13.7 13.6 13.0 14.4 14.5 12.9
VI
PI
P8
--4V
I
Av. 13.7 & 0 . 5 a
Not included in average because of gas evolved.
(2) the change in bond character from largely densely packed structures below the melting point, covalent in the solid to something intermediate but calculation of the volume change were they t o melt directly may be made. Nothing is known between metallic and ionic in the liquid. Were the transition simply an increase in the about the density of liquid CdTe, but the other coordination number of hard spheres from 4 to 8 substances show a regular decrease in volume conthe contraction would be 50%. The observed tractionfromgraysn ( - 1 7 . 5 % ) - t o y A g I ( ~ + 3 % ) . decrease is far less, one of the major reasons being No correlation of this trend with melting ,temperathe increased kinetic energy of the liquid, with ture or transition temperature exists, but there is larger amplitudes of atom vibrations about their a regular variation with the electronegativity difmean positions. Voids of varying size, present ference for the two elements of each c o m p ~ u n d . ~ because packing in the liquid only roughly ap- It thus appears that the effect of increased bond proximates the regularity of a crystalline lattice, ionicity, not evident in the interatomic distances also diminish the effect. in the solids, becomes effective in the liquid state. For the zinc blende type substances an additional Acknowledgments.-The research described in important factor appears t o be the increase in this communication was in part supported by the interatomic distance in the liquid associated with Air Force Office of Scientific Research under Conincreasing ionic character in the bonding. This is tract No. AF-18(600)-1489 with the University of suggested by a comparison of the volume changes Chicago. The authors wish t o express their in the isosteric sequence: Sn (gray), InSb, CdTe thanks to the Chicago Midway Laboratories for and y-AgI. All are iso-electronic, with a mean supplying the indium antimonide used, and t o atomic number of 50. The observed interatomic M. C. Bachelder and A. Leoni for their work in distances are almost exactly the same (2.80 A.) analyzing the material. for the solids. Two of the substances (Sn and y-AgI) undergo phase transformations t o more (9) E. Mooser and W. B. Pearson, J . Electronics, i, 629 (195G).
*
NOTES SOLID-LIQUID EQUILIBRIA OF T H E SYSTEM URANIUM HEXAFLUORIDECHLORINE TRIFLUORIDEl BY W. S. WENDOLKOWSKI A N D E. J. BARBER TechnieaE Division, Oak Ridge Gaseous Diii'usion Plant, Union Carbide Nuclear Company, Oak Ridge, Tennessee Received December 19, 1367
Investigation of the solid-liquid equilibria of the system uranium hexafluoride-chlorine trifluoride was undertaken as a part of a series of studies of the basic chemical and physical properties of the interhalogens. The entire range of compositions from ( 1 ) This document is based on work performed at the Oak Ridge Gaseous Diffusion Plant operated by Union Carbide Corporation for the U. S. Atomic Energy Commission. Presented at the 132nd National MeeLing of the American Chemical Societj, New York City, September 8-13, 1957.
0-100 mole % uranium hexafluoride has been studied using the techniques described by Skau2but modified so as to insure equilibrium during the melting and freezing cycles. Experimental Materials.-Commercial uranium hexafluoride containing less than 0.015 weight yo impurities, principally hydrogen fluoride, was purified further by repeated removal of the vapor phase over the liquid. The resulting material melted a t 64.04' and was not less than 99.9 mole % uranium hexafluoride. Purified chlorine trifluoride was produced by passing the commercial material over pellet,ized sodium fluoride a t 25' to remove any hydrogen fluoride and then distilling in a twenty plate, nickel column packed with inch nickel helices. The distillate which boiled a t 11.75' at 760 mm. pressure and melted at -76.34", was found to be 99.96 mole % chlorine trifluoride by thermal analysis (assuming ClFs to be monomolecular). (2) E. L. Skau, Proc. A m . Acad. Arts Sci., 67, 551 (1933).
c
