KOTES
37s
T'ol. 65
TABLE I X-RAY( H I G ITEMPERATURE ~ CAMERA) RESULTS FOR VARIOUS HEATTREAThIEPL'TS OF TIIE 90: 10 CsCI-RhC1 Film no.
La-31
PrehEat,b
C
398
Subsequent treatment
Exposed to X-rays a t oncec
X-Ray lines after 4 hr. Exposure to Mo rays Pm3m Fm3m
Remarks
Above completion temp. of Pm3mFm3m previously found a t 395" La-40 392 Evposed t o X-rays a t onceC Weak Strong Below completion temp. of Pm3mFm3m La-41 392 Cooled to 1%'-exposed to X-rays at oncecjld Medium Strong With Pm3m initially present, the amt. of this phase became greater upon cooling La-30 423 Cooled to 68°-exposed to X-rays a t once Strong Medium Strong Pm3m lines-low reappearstrong ance temp.-delayed unmixing of Fm3m solid soln. indicated This mixture was melted, cooled to room temperature and reduced to a fine powder by grinding. The fine powder was screened through a 200 mesh sieve and placed in a fine capillary tube for X-ray analysis. After each X-ray exposure, the sample was allowed to cool to room temperature (this wa8 necessary for the removal of the film from the camera). This temperature was: approached from below and maintained constant (&0.75O) by careful hand control for 30 minutes before X-ray exposure. Temperature maintained constant (10.75') during X-ray exposure by means of thyratron control. This temperature was approached from above and care was taken not to drop below this selected temperature a t any time.
Rapid cooling of melts containing one to five mole per cent. of rubidium chloride exhibited the click phenomenon but slow cooling (cooling over a period of from three to five hours) of these mixtures brought about gradual unmixing of the solid solution and no sudden evolution of heat corresponding to the click phenomenon was observed.2 The high temperature solid solutions were readily formed again by reheating from below the click temperature (curve B). Upon cooling these reformed solid solutions however, the click phenomenon never was observed although the high temperature X-ray camera showed definitely that the phenomenon of delayed unmixing again occurred. It can now be concluded that the audible sound observed simultaneously with the click phenomenon 1i3 caused by the sudden shattering of the relatively large solid solution crystals obtained directly from .the melt. The white mass resulting from the delayed unmixing of these large crystals was found to be made up of extremely fine crystals3 of Pm3m cesium chloride and residual Fm3m solid solution and the extreme brittleness of the white mass (described above) obviously is due to this mixture of fine crystals. Heating these small crystals to a temperature above curve A forms only small crystals of the Fm3m solid solution which crystals do not produce an audible click as they unmix upon cooling. Working with a 9O:lO mixture of these small crystals it wa,sfound possible to delay greatly the beginning of uinmixing by rapid cooling in a capillary tube. Th.e 90: 10 mixture was first heated in (2) I n 1910, S. Zernczuzny and F. Rambach reported (2.anorg. Chem., 6 5 , 418 (1910)) freezing curves for small additions of either potassium chloride or rubidium. chloride to cesium chloride in rough approximate agreement with the first part of curve A rather than curve B. This report would seem t o indicate that rapid cooling might be required t o cause a delayed Fm3m-Pm3m transition as represented by curve B. (3) A small amount of a n 85: 15 molar mixture of cesium chloride and rubidium chloride w & s melted a n d drawn into a capillary sample tube where i t was allowed to freeze and then cool through the click temperature range t o room temperature. Even though the sample was not ground and screened as is usually done, satisfactory X-ray lines were nevertheless obtained which showed clearly t h a t the unmixing of the d i d solution associated with the click phenomenon produced a mixture of very fine powders.
None
>\IIXTCREn
Strong
the high temperature X-ray camera t o a few degrees above curve A (423"-Table I) until re-formation of Fm3m solid solution was complete after which the sample was cooled to a series of successively lower and lower temperatures (with reheating to 423" between each test) until the appearance of the low temperature (Pm3m) form of cesium chloride was first observed a t 68" (La-30). This long delay in unmixing was avoided by beginning the cooling from just below curve .A at which point the mixture still contained a trace of t>he low temperature cesium chloride (La-41).
HEATS OF FORMSTIOIV OF a-PHASE SILVER-INDIUM -4LLOYS' BY RAYMOND L. ORR A Y D RALPHHULTGRES Department of Mznernl Technologzi, Unzaersit?~of Californza, Berkeleu, Cali/omza Recezued Julu 29, 1960
Heats of formation of the Ag-rich terminal CYsolid solutions of Cd, In, Sn and Sb in Ag a t 723" K. have been measured by Kleppa.2-i The trend in the experimental values showed the heats of formation to become less exothermic with increasing atomic number of the solute except for In, which forms a more exothermic solution than any of the others. This could be interpreted as indicating an anomalously high affinity between Ag and In. However, in other criteria of bond strength such as the effect of solutes on the lattice constant of silver, In falls in a normal sequence between Cd and Sn. It therefore seemed worthwhile to independently measure heats of formation of solid solutions of In in Ag. This has been done as reported in this paper. The relationship between heats of formation and bond strengths also is discussed. (1) This work sponsored by Office of Ordnance Research. U. 9. Army. (2) 0. J. Kleppa, J . Am. Chem. Soc., 7 6 , 6028 (1034). (3) 0.J. Kleppa, Acta M e t . , 3, 255 (1955). (4) 0.J. Kleppa, THIS JOURX.AL, 60, 846 (1956).
NOTES
Feh., 1961
379
Experimental Preparation of Alloys .-Four Ag-In alloys containing 5 .O, 9.0, 15.0 and 17.0 at. % In, all in the f.c.c. a-solid solution range, were prepared by melting the pure metals togethe: in sealed evacuated Vycor tubes and homogenizing about 50 below the respective solidus temperatures for two weeks. The Ag and I n used in the preparations and also for meas% purity. urements on the pure metals were of 99.9 Sharp well-resolved X-ray diffraction lines obtained from annealed filings taken from both ends of each ingot indicated the alloys to be homogeneous. Measured lattice constants were in good agreement with published data.s-6 Apparatus and Methods.-Heats of solution in liquid Sn of Ag, I n and the alloys were measured using the calorimetric apparatus and methods described previously.7v8 Samples mere dropped from an initial temperature, Ti, near 317" K., into the tin bath a t temperature T f , near 700°K. The heat capacity of the calorimeter was determined by dropping specimens of pure Sn. The balanced heat effect method, described previously,' was used to reduce the magnitudes of the measured heat effects and the associated heat transfer corrections. Heats of formation a t temperature Ti were obtained by subtracting the heats of solution of the alloys from the heats of solution of corresponding amounts of the pure metals. During the runs the concentration of solute metals in the liquid Sn bath never exceeded 2 at. %. Within this dilute range any concentration effects were negligible within the experimental uncertainty.
+
Results Results for the pure metals are given in Table I. From the measured values together with known heat content dataj9the relative partial molar heats of solution of Ag(s) and In(s) in Sn(1) for xsn = 1 at 700°K. were evaluated and are given in the last column. Results for the alloys are given in Table 11. The heats of formation have been referred to a common temperature, 317"K., the mean value of T i for the alloys. The heats of formation are plotted in Fig. 1 together xyith those of Klema4 whose values a t 723" K. were measured with respect to Ag(s) and In(1). For purposes of comparison, the values plotted have been recalculated to refer to superheated In(s) a t 723"K., using 780 cal./g.-atom for the heat of fusion of 111.~ TABLE I HEATSOF SOLUTION OF PURE METALSIN LIQUIDTIN AHmem
Run no.
Solute
Ti,OK.
TI,OK.
cal.jp.? atom
45-3 45-11 46-4 46-12
Ag Ag Ag .4g
317.9 319.2 314.2 315.0
698.5 698.5 700.3 700.4
6271 6238 6303 6273
-% 45-4 45-12 46-11
In In In In
AH^,,^^.. ?noOK.. cal./g.-atom
Av. 317.9 319.3 314.7
698.6 699.0 700.4
3267 3186 3254 Av.
3865 3838 3863 3830 3850 -185 -260 -232 -226
Discussion The presently reported data and those of Kleppa are in excellent agreement. Kleppa's values at 19 ( 5 ) E. A. Owen and E. W. Roberts, Phil. Mag., 27, 294 11939).
(6) W. Hume-Rothery, G. F. Lewin and P. W. Reynolds, Proc. Roil. SOC.(London), 8 1 5 1 , 167 (1936). (7) R. L. Orr, A. Goldberg and R. Hultgren, Reu. Sci. Instr., 28, 767 (1957). ( 8 ) R. L. Orr, -4.Goldberg and R. Hultgren, THISJ o n ~ x a L 62, , 325 (1958). (9) K. K. Kelley, U. S. Bur. iMines Bull. 584, 1960.
I
-1500 0
l
4
2
I
l
8
1
1
1
12 14 16 ATOMIC PERCENT I n ,
6
IO
18
20
Fig. 1.-Heats of formation of a-phase Ag-In alloys.
HEATS O F
TABLE I1 FORMATION O F Ax-In ALLOYS AT 317°K. -
Run no.
Alloy comp., at. % I n
Ti, OK.
45-6 46-10 45-7 46-8 45-8 46-7 45-10 46-6
5.0 5.0 9.0 9.0 15.0 15.0 17.0 17.0
319.3 314.8 318.7 314.9 ,318.8 314.5 318.9 314.6
AHeo~n.,
Tf,OK. 698.7 700.3 698.7 700.3 698.7 700.3 698.8 700.3
d./g.-
AHform.d17OK.,
atom
cal./g.-atom
6559 6584 6763 6796 7004 7038 7041 7082
-
461 448 783 782 1206 - 1203 1304 1309
-
-
at. ?' & In have been included in Fig. 1, even though they were thought by that author to be well within (CY {) two phase region. The recent evaluation of Hansenlo indicates that the a-phase extends to 19.5 at. % In a t Kleppa's temperature of measurement, 723°K. The present data are well represented by the equation
+
AH
- = -9100
XIn
+ 49000X2I,
shown by the curve in Fig. 1,with an average devjation of less than 4 cal./g.-atom. The value of A H I ~ a t xhg = 1 is thus -9100 cal./g.-atom. Because of the extremely small scatter in the present results and their unusually excellent agreement with those of an independent investigation, the uncertainty in the selected curve is thought to be only about f10 cal./g.-atom. (10) M. Hansen and K. Anderko. "Constitution of Binary Alloys," 2nd Edition, MoGraw-Hill Book Co., Ino., New York, N. Y., 1958.
NOTES
380
The exact :agreement between the heats of formation a t 317 and 723°K. indicates that ACp = 0 for the a-phase alloys within this temperature range. The same observation was made for the a-phase Ag-Cd alloys,*where close agreement with Kleppa's data also was3 obtained. The solid solution of In in Ag is indeed more exothermically formed than that of Cd in Ag. Calculations by Kleppa4 based on a method by Friedel do prladict that the limiting heat of solution of In in Ag should be more exothermic than those of Cd, Sn and Rb, resulting from the relatively low first ionization potential for In. The quantitative agreement however is poor due to the approximations involved in the model. For one thing it seems unlikely that In, or the other solute metals, would contribute only one valence electron to the conduction band of Ag as that model assumes. For this series of alloys the concentration limits of a-phase stability decrease regularly with solute metal valence, and the electron to atom ratio at those limits is relatively constant (1.2-1.4 at room temperature) in accord with Brillouin-zone theory. This suggests that all the iralence electrons of the solute atoms enter the Ag conduction band. Heats of formation are not, however, an absolute measure of bond strength. Rather, they represent the difference between total bond energies of products and reactants, and thus for alloys are relative to the bond strengths of the pure component metals. The highly (exothermic result for the reaction (1 - z)Ag(,, zIn(,) = Agl-.In,(,) need not be taken as indicating an anomalously high stability for the alloy; it might just as well arise from an anomalously low stability for elementary In. Such considerations must always be kept in mind in attempts to relate intermetallic bond strengths to heats of formation.
1701.
05
sminoethy1)-pyridine wm prepared, m.p. 140°, literature4 138-139',' as well as a dipicrate, m.p. 102", l i t e r a t u r ~ ~ 192.8-1 95.2'.
The preparation of solutions of metal ions, measurements and calculations were performed as described previously.2 The results are assembled in Tables I1 and 111. Attempts to obtain values for Zn++ and Cd++ at 10' with 6-methyl-2-picolylmethylamine indicate that the complexes are too unstable for measurement. With Ag+ at 30" the calculated K's are not constant. With both 2(K-piperidin0)- and 2-(N-pyrrolidino)-ethylamine. in combination with Co++, Zn++ and Mn++, the formation of precipitates prevented the determination of any constants, With 2-(2-methylaminoethyl)-pyridine no consistent constants could be obtained for Cu++ and Ni++ while Ag+, Zn++ and Co++ yielded precipitates.
Discussion
The compounds under consideration here permit one to make comparisons with compounds which have less steric hindrance to coordination. The compounds 2-picolylamine, 2-picolymethylamine, 6-methyl-2-picolylamine and 6-methyl-2-picolylmethylamine show only slight differences in basicity (pK1a t 30" = 8.51-8.8). The effect of substitution of hydrogen is to increase basicity slightly, more when substitution is on the primary amine group than on the pyridine nucleus. (Substitution has little or no effect on pKz.) However, the formation constants of the copper derivatives decrease in the order in which the amines are listed log K ~ a t 30": 9.45, 7.80; 9.27, 6.55; 6.81, 5.65; 6.48, 4.94. The effect of methyl substitution is to decrease stability. For 2-picolylmethylamine the decrease is slight for the coordination of the first ligand and large for the second ligand. For the amines with substitution in the 6-position on the pyridine ring the decrease is large for the coordination of both ligands and slightly more so for the FORMATION COXSTANTS OF 6-METHYL-% coordination of the first ligand than for the second. PICOLYLMETHYLAMINE WITH SOME The changes in the heat of formation follow those in log K (or free energy). The same statements COMMON METAL IONS' hold for coordination with Xi++ except here the BY RODNEY E:. REICHARD ASD W. CONARD FERXELIUS presence of the methyl group in the &position on Department of Chemistry, The Pmnnylvania State L'nieersity, Uni?ers;tU the pyridine nucleus blocks the coordination of the Park, Pennsylvania third ligand molecule. Received August 10, I960 The relation between 2-(2-aminoethyl)-pyridine Formation constants for the association of some and 2-(2-methylaminoethyI)-pyridineparallels that common divallent metal ions with 2-picolylamine, between the corresponding picolyl compounds. 2-picolylmethylamine, 2-arninoethylpyridine,* and Methyl substitution on the primary amine group 6-methyl-2-picolylamine3 have been published. increases pK1 slightly and decreases pKz slightly. These studies are now extended to include 6- However, due to the general lowering of stability methyl-2-picolylmethylamine and 2-methylamino- by the increased size of chelate ring, the complexes ethylpyridine with incidental observations on 2- of the methyl-substituted compound are too small (N-pyrro1odino)- and 2-(S-pipcridino)-ethylamine. for detection by the potentiometric method. The N-piperidino- and N-pyrrolidino compounds Experimental The amines were commercial products which were first are cyclic substitution products of ethylenediamine distilled under va,cuum and then dissolved in triply-distilled, (p& and: at.30". = 9.81 and 6.79).* Here the effect air-free water. Roiling points and neutral equivalents are of substitution is to increase slightly the pK1 for a reported in Table I. The monopicrate of 2-(2-methyl(4) K. L6ffler, Ber., 37, 161 (1904). ( 5 ) H. E. Reich and R. Levine, J . A m . Chem. Soc., 77, 4913 (1955). (1) This investigation was carried out under contract AT(30-1)-907
+
between The Penniiylvania State University and the U. S. Atomic Energy Commission. ( 2 ) D. E. Goldberg and W. C. Fernellus, THISJOURNAL, 63, 1246
(1959).
(3) I I . R. Weimer and N. C. Fernelius. ibid., 64, 1961 (1960).
(6) J. Van Alphen, Rec. trau. chim., 68, 1105 (1939). (7) E. Munch a n d 0. Schlichting, German Patent 561,136, Dec. 19. 1930; c. A . , a7, 9959 (1933). (8) G. 11. McIntyre. Jr., B. P. Block and W, C. Ferneliue, J . A m . Chem. Soo., 81, 529 (1959).
P
