GENEF. DAYAND R A L PL~WLTGREK ~
1532
TABLE 111 DERIVED RESULTSAT 298.15'K., ------Valueu C0m p o u n d
COnd0naed atnto
4-Pluorotoluene 1 ,ZDifluorobmzene 1,3-Difluorobennene 1,4-Difluorohenzene m-Trifluorotoluic acid
Liquid Liquid Liquid Liquid Solid
AHGO
67 f 0 17 -707 33 f . l a -703.99 -17 -704 39 =I= -13 -796.14 f .14 -894
*
samples of 712characteristic NevertheIess, in other irn-
THERMODYNAMICS
~o~n-1
for condensed state---
AE?
apparent difficulty in preparing pure trifluorotoluic acid is an undesirable for a proposed reference sukstance. m-trifluorotoluic acid is BR tisfactory
KCAL.
Vol. 66
-896.56 & 0 17
-70'7,62 .13 -704 28 rt .17 -704.68f
.l3 -795.85 & .14
-7
ARf*
- 43.43 78 30 - 79.64 - 79.24 -251.78
-
AMl*
8.42 i 0.02 8 85 =I= 02
AIij" (W)
-34 01 -67.65
8 29 f .05
-71.35
8.51 +E .05
-70.69
portant respects, and the purity problem could be solved if an appropriate organization prepared a suitable large sample for distribution t o qualified investigators.
OF THE GOLD-NICKEL SYSTEM
BY GESE F, BAY'^ AND RALPHHTTLTCIRREE;'~ Department of Mineral Technologg,
v?ViUeTS~@of
California, Berkeley, Callfornaa
Rsoerved April 1.6, 106B
The heats of formation of five gold-nickel alloys have been nieasured at 1150OIC by liquid tin solution calorimetry. The results have been correlated with other thermodynamic data and the equilibrium diagram for the gold-nickel system. Yree energy, heat, and entropy values have been tabulated for the solid alloys. For a 10 atom %, nickel alloy, the enthalpy relative to room temperature has been measured to 125O"Ii.for comparison with ACp values in the literature. Lattice parameter and density measurements indicate that the vacancy concentration in the quenched alIoys is not great, in contradiction to previously reported results,
Introduction nearIy with measured densities,. As has already The gold-nickel system has recently been in- been rnen-lioned in a technical note,6 this fact was vestigated a number of times v i t h the objective of not confirmed in this rork. Seigle, Cohen, and Averbach' report e.m.f. elucidating crystal chemical principles. The system wag chosen as an example of an endothermic measurements of solid alloys. Free energies calalloy system, possessing a miscibility gap which culated from these data agree reasonably well with closes above 1084'11. and a minimum in the the miscibility gap boundaries except for x~~ c0.3. liquidus and solidus curves2 (Fig. 1). Results have Howe.\-er,entropies and heats of formation derived from their temperature coefficients seem improbabeen somewhat less than satisfying. Flinn, Averbach, and Gohens examined alloys bly high8 as do AC, values derived from the change for atomic arrangement by Fourier analysis of of these quantities with temperature.0 Oriani and Murphy, 10 studying gold-rich and X-ray diffraction patterns. They found, to their ' surprise, evidence of short-range order rat,her than nickel-rich compositions (2-22 and 95-98 atom % the expected tendency toward clustering (atoms Xi), found heats of formation of solid alloys much surrounded preferentially by like atoms). They smaller than those indicated by Seigle, Cohen, and concluded that the yuasichemical theory was iiot Averbach. I n another investigation,ll by direct adequate and at>tributedthe tendency t o order to reaction of the elements, they found heats of formaatomic size differences. IIowever, a fern years tion of liquid alloys much less endothermic than later Miinster and Sagel&repeated the study and those of the solid state. DpSorboi2and Orianiis measured heat capacities found clustering in the alloys. Ellwood and Bagley5 measured lattice param- and heat contents of a single alloy (48.3 atom % eters and densities of the alloys. At two composi- Xi). DeSorbo found that between 13 and 298.tions (20 and 90 atom yo Ni) they concluded that 15°K. a positive derivation from the Kopp-Keuabout 3y0of the lattice positions were vacant, while mann rule (AC, >0) accounted for about 0.51 a t other compositions X-ray densities agreed more cal./g.-atom deg. of excess entropy for the alloy. (1) (a) Graduate Research Engineer, Department of Mineral Technology, University of California, Berkeley. (b) Professor of Metallurgy, Department of Mineral Technology, Unirersity of California, Berkeley. (2) M. Hansen, "Constitution of Binary Alloys," McQraw-Hill Book Co., New York, N. Y., 1958. (3) P. A. Flinn, B L. -4verbach. and M. Cohen, Acto Met., 1, 604 (1953). (4) A. MUnster and IC. Sagel, Paper 2D, Proceedings, Symposium No. 9, National Physical Laboratory, The Physioal Chemistry of Metallic Solutions and Interrnetallio Compounds, H. M. S. O., London, 1959. (8) E. C. Ellwood and K. Q. B d e y , J . Inst. Metals, 80,617 (1952).
(6) G. F. Day, 0.3. ~
Experimental Gold and tiickel of 99.95% purity were used. Weighed amounts of each were sealed in evacua,ted capsules of fused quartz, then heated to temperatures 50-150' above the liquidus for each co.mposition. After several minutes of severe agitat.ion a t temperature, the capsules were plunged into cold water so that the ingots, which weighed from 5 Lo 10 g., would freeze with a minimum of macrosegregation. In every case the loss in weight amounted to less than 0.01 %, so that the final composition was taken LO be the sanie as that initially weighed out. After cold working, the ingots were sealed in evacuated fused quartz tubes and homogenized for more than a week a t temperatures about 50" below the solidus and m r e rapidly quenched. Filings were then taken from both ends of each ingot, annealed for 1 hr, in the single phase region, and quenched rapidly in cold water. Back-reflection X-ray lines proved to be sharp, assuring homogeneity of the ingots. Precision lattice constants were determined from these lines. Values obtained were found t o agree fairly well with those of Ellwood and Bagley, but follow a smoother curve with composition.6 Densities were det'crmined by measuring the buoyancy of the ingots in distilled water.* Thew results indicated very few vacancies, in contradiction t o the work of Ellwood and Bagley. The liqiiid tin solution calorimeter has been descrihcd elsewhere,'+ so the procedure will be described only briefly. [Small chips of the ~ l l o y swert: eticapsulated in gold foil to make mniplec: about 5 min. in diameter and weighing approximately 0.5 g. iipecimeriv were introduced into the dispenser and held there at about 1150'H. for about 15 min. before being chopped into the calorimeter bath which was contained in tjhe same evacuated space. Previous tests had shown that prolonged heating of the ~ramplesa t 1160'K. produced neg1.iyible reaction between the alloy and gold foil. The tin hath was maintained a t approximately 910°K.; at lower temperatures the pure nickel samples did not dissolve rapidly enough for accurate measurement of the heat evolved. Heats of solution were determined in the usual manner. After correct.ing for the heat effect of the gold foil, heats of solution of alloys minus heats of solution of their corn-. ponents yielded heats of formation of the alloys a t the initial. temperature, a,bout ll50'K. Concentrations of impurities in the tJin bath were held below a total of 0.9 atom %. Within these limits their effect on the heat of solution of pure gold was found to be negligible; the heat of solution of nickel in tin was found to depend on the nickel concentra(14)
R. L. Om, 4. Goldbera;, and R. Hultgren, RBU.Sci. Instr.,
767 (1957).
1533
THERMODYNAMICS OF THE GOLD-NIC:EEL SYSTEM
0
0.4 0.6 0.8 ATOMIC F R A C T I O N N I C K E L .
I. 0
0.2 X,i,
Fig. 1.-Phase diagram of the gold-nickel system. tion in the bath, however. A small correction was made for this de endence. The experinieiital results are shown in Tables and 11.
?
TABLE I HEATSOF S O L ~ ~ TAT I O910'K. N
Sample
Au
Ti,'I, The Physical Clieiiiisti y of Vetallic Solutions and Intermetallw Compounds, H M 3. 0 ,I,ondoh, 1959
I ,
riT
IC
800
I\'
900 1000 1100 1150 1200
1250
~ AChP4( Y 1'1 Ii
G 728 (i 857 6 987 7 115 7 178 7 241 7.312
6 838
7 7 7 7 8
065 280 609
793 040
8 387
ANI1
1
0 , I l CD\" - 0 , I Cpyi
C,' alloi
3243 3940 4655 5395 5780 6180 6590
H m
b 6130 0 ii31 b 8t12 0 002
BOH l H E LLLOY f i U o 9%
- Hms
-
T - 298 420 469 530 655
6 bl!)
SMC)UTIIEL) VAI,[JY:S 03' U N L ~ T I I A L I ' Y , H
1ip 2 -Integral heitts of formation of solid hu-Ki alloys
=
G G 0
3224 3851 ,3905 4728 5040 5260 ti202 0532
NI
x N ~
AI&,
- Hiss
X",,
0 100
198 ,2UJ
494 615
I799 1 075
them into agreemeiit with the-miscibility gap COW ditioas. The new values of AF,, are more negative and result in the integral free energy being 150 cal.jg.-atom more negative a t ~ C N= ~0 4 than was origiiially reported7 Table T' gives the thermodynamic fuiictions resulting from these data and the measured heats of formation. 6
TIHI 1 S B L h l I hl)
t'Hh€tM(JU1AAMl(
t%?
