The heats of formation of solid nickel-copper and nickel-gold alloys

THE HEATS

OF FORMATION

OF SOLID NICKEL-GOPPER R. A. ORIANII

and

AND NICKEL-GOLD

ALLOYS*

W. K. MURPHYf

The enthalpies of formation at 640°C of solid Ni-Cu and Ni-Au alloys have been measured as a function of composition by means of a differential solution calorimeter. Both systems are characterized by positive heats of formation. The conoentration variations of the partial molar heats of solution of Cu and of Ni in liquid Sn at 640°C have been explored. It is shown that Cu in Sn does not satisfy the requirements of the quasi chemical theory, whereas Ni in Sn does so within experimental uncertainty. LES CHALEURS

DE FORMATION

DES ALLIAGES

CUIVRE-NICKEL

ET OR-NICKEL

Los enthalpies de formation it 640°C des &ages solides de cuivre-nickel et d’or-nickel ont et&mosurees en fonction de la composition it I’aida d’un ealorimetre differentiel. Les deux systemes sent caracterises par des chafeurs de formations positives. Les auteurs ont Bgalement examine les variations, des chaleurs partielles molaires de solution du cuivre et du nickel dans l’etain liquid0 a 640°C en fonction de la concentration. 11s ont montre que pour le ouivre ces variations ne sat&font pas aux oxigences de la theorie quasi chimique tandis que celles du nickel dans l’etain y repondent bien, compte term des erreurs experimentales. WARMETONUNGEN

VON

NICKEL-KUPFER

UND

NICKEL-GOLD

MISCHKRISTALLEN

Die Bildungsenthalpien von Ni-Cu und Ni-Au Mischkristallen wurden bei 64O’C als Funktion der Zusammensetzung mit Hilfe sines differentiellen LBsungskalorimetersgomessen. Beide Systeme weisen eine positive Bildungswarme auf. Die Andernugen der partiellen molaren Lasungswiirmen van Cu und Ni in fltissigem Sn bei 640°C wurdan in Abhlingigkeit von der Konxentration untersucht. Es zeigt sick, dass Cu in Sn die Forderungen der quasiohemischen Theorie nicht erfiillt, wilhrend diese bei Ni in Sn innerhalb der experimentellen Unsicherheiten erftillt sind.

chambers until they have attained the same temperature as the solvent tin, whereupon the metals are dropped into the respective solvent containers. The difference between the heats of solution in the two solvent containers is observed through an amplified differential thermocouple signal which is recorded before, during, and after the dissolution of the metals. Each cell was calibrated electrically at various solute concentrations during the course of the experiments; when the metal concentration in the tin reached about 5 at. y$ that charge of tin was replaced by a fresh charge. If the in~~idual calibration factors of the two cells differed by more than the sum of the uncertainties in the knowledge of those calibration factors, then the apparent heats of formation were corrected for the deviation from twinness of the two cells. Because of the slow rate of dissolution of pure nickel and of the nickel alloys into liquid tin, the calorimeter was operated at 640°C at the fastest available stirring rate. This high temperature, however, causes an appreciable deviation from Newtonian cooling, leading to greater difficulty in a~~ount~g for the heat lost during the long dissolution process. These difficulties, coupled with the smallness of t,he heats of formation, account for the magnitude of scatter in the final results.

The solid solutions of nickel and copper are of interest because of the desirability of attempting to observe the energetic effect of the filling of the d-shell vacancies in nickel that occurs as copper is dissolved in the nickel. The nickel-gold alloy system is of interest because of the apparent anomaly represented by the finding(i) of positive short-range order in a miscibility gap system. The thermodynamics of this system has already been investigated(2) by a galvanic cell technique, but, because of the well known difficulties associated with the evaluation of properties that depend upon the temperature derivative of the cell e.m.f., it has been deemed wo~hwhile to carry out calorimetric measurements of the enthalpy of formation of the terminal solid solutions. EXPERIMENTAL

The calorimeter employed in this work has been described in detail elsewhere.c3) It is a d.iRerential solution calorimeter employing liquid tin as solvent, one cell of which receives the alloy and the other cell the corresponding amount of the pure metals. The alloy and the metals are held in separate discharge * Received March 6, 1959.

7 General Electric Research Laboratory, Schenectady, New York. Now at U.S. Steel Corporation, Edgar C. Bain Laboratory for Fundamer&al Research, Monroeville, Pennsylvania. ACTA METALLWRGICA,

VOL. 8, JANUARY

1960

23

ACTA

24 TABLE

Ag (5) Ni (s)

VOL.

8,

1960 DISCUSSION

1. Partial molar heats of solution in liquid tin

/ Deviation from ’ lea&-squares

aH% (8) (c&/g atom)

cu (s) i

METALLURGICA,

425 640 306 450 640 640

It has previously been pointed out(4) that the variation with concentration of the partial molar heats of solution of the liquid noble metals in liquid tin at low concentrations cannot be described by any variant of the quasi-chemical model that assumes the constancy of the pairwise interaction energies. The same statement can be made for the present data for Cu in liquid Sn at 640°C. However, it is interesting, though fortuitous, that the concentration variation for liquid nickel dissolved in liquid tin does agree, within experimental uncertainty, with the Bragg-Williams approximation.

RESULTS

The variation with concentration of the partial molar enthalpy of solution of solid copper and of solid nickel into Iiquid tin at 64O’C has been obtained incidentally to the main investigation. This information is of interest in connection with the adequacy of statisticalmodels for describing verydilutesolutions.(Q The present results, to which have been added relevant data from prior work,(*) are collected in Table 1. The equations for ms(.s) for solid Cu and Ni at f14O”Crepresent the present experimental work up to a solute concentration in tin of 0.013 mole fraction, whereas the equations based on prior work(p) at the lower temperatures represent data up to a solute concentration of 0.02 mole fraction. Fig. 1 presents the enthalpy of formation of solid Ni-Cu solutions from the solid components at 640°C. The vertical bars represent the mean deviation of the data, based on at least three totally independent determinations at any one composition. The accuracy of the data may be partially evaluated from the estimated inaccuracies of shout &0.5 per cent in the knowledge of the calibration factors, and about 10.2 per cent for the chemical composition of the alloys. The enthalpy of formation of solid Ni-Au solutions is shown in Fig. 2; a dotted line represents the course of the curve in the two-phase field.

0.2

0.4 Atom

0.6 fraction,

O-8

I.0

Ni

Fm. 1. The enthalpy of formation of nickel-copper solid solutions at 640%; the reference state is the pure components a& 640°C.

The results in Table I show that (~A~~/~x~)~ for both Cu and Ag varies markedly with temperature, but the physical reason for this varia#tion is not at all understood.

‘~ 1000

900

‘\

'Y

800

x

600

I

-

‘l

4

9-JE

500

IA

% 400

‘\ \ \

\ ‘1

200 100 300

\ ‘;

ATOM

FRACTION

Ni

FIG. 2. The enthalpy of formation of nickel-gold solid solutions at 640°C; the reference state is the pure components a,t 6W.C.

~ubaschewski et I&.(S) have obtained a value of about 540 Cal/g atom for the enthalpy of formation of equiatomic Ni-Cu solution at 722°C by means of a reaction calorimeter. Since the AH, of these alloys may have some temperature variation because of the ferromagnetic character of nickel, it cannot be stated whether or not there is agreement between these authors’ work and the present data at 640°C. The same comment applies more strongly to the preliminary results of Leach(“) for the AH, of solutions in the cornposition range 20-40 at y,bnickel in copper

ORIANI

at 0°C. of

AND

FORMATION

MURPHY:

The present results confirm calculated

AH,

for

markedly

Cu-Ni

with

Verma(@,

by

the

Meijering”)

calculations

who propose

a AH,

but

of

OF

values disagree

Rastogi

and

curve rising to 2000

NICKEL-COPPER

instead The

AND

of the

excess

1.47 Cal/g atom-deg

entropy

of formation

compared with the value of 1.07 f measured

by

DeSorboos)

and

Cal/g atom at xxi = 0.3, and dropping to -7500

Cal/g

vibrational

contribution

to

atom at xxi = 0.8.

AH,

formation.

This

that

The positive

character

of

means

for Ni-Cu found in the present work is in qualitative

alloy has a magnetic

agreement with the positive excess free energy of solution found by Naniscg) and by Pratto”), both by

formation

electrochemical

exhibits

cells, and that calculated by Alcock

from the measurements the

solubility

positive

of

of Fukusima

hydrogen

and Mitui(i2) on

in Ni-Cu

nature of the AH,

alloys.

The

leads one, according

to

the quasi-chemical model, to expect clustering (negative short-range order) in the Ni-Cu solid solutions. It is interesting that Kiister and Schi_ile(13) have

concluded

that

clustering

of reference

2.

of 0.4 must

be

0.2 Cal/g atom-deg @iani

for

excess

the equitomic

to the entropy

short-range

disagrees with that of Flinn et al.(l) in finding negative, not positive,

short-range

order.

The present

because,

even

ambiguously

though

associates

quasi-chemical a positive

theory

there need not be a correlation

such

the two.c4)

This is basically

susceptibility

upon neutron

extent upon

of short-range the

relative

energies among

The scatter in the present results for Ni-Cu prevents

pure components; magnitude

due to the completion

the properties

in nickel

feature of the AH,

of the filling

at

xcU = 0.6.

of the d-shell An

interesting

curve is the marked assymmetry,

such that the addition of Cu to pure Ni leads to a much larger endothermic

effect than does the addition

of

Ni to pure Cu. The present results for the Ni-Au 640°C

show

positive

values

expected for a miscibility are smaller, by

Seigle

technique

at 900°C.

of about

cannot

surmise enthalpy

alloy.

the two

be reconciled

through

of Kubaschewski of formation

as evidencedo5)

of formation

present

cell

between

variation of the AH,, The

than those

a galvanic

The disparity

by the smallness of the AC, equitomic

two,

aZ.t2) using

et

sets of data probably the temperature

AH,, as is to be The magnitudes

gap system.

by a factor

obtained

for

solid solutions at

results

of an almost confirm

the

and Catterall(16) that the

is probably

smaller than that

given by Seigle et al. and agree qualitatively with the preliminary calorimetric results of Genta. If one assumes that the excess free energy of formation as measured by Seigle et al. is correct, though the quantities depending on the temperature dependence of the galvanic cell e.m.f. are not, and if one adopts a value, extrapolated from the present work, of about 1500 cal/g atom for the heat of formation at 900°C for Ni,,, Au,,~, one obtains

ABe m 0.4 Cal/g atom-deg

order, physically because

and more

the various

of the

between

the kind and

order in the solution

values

exist in the solution,

us from seeing the effect, if any, upon the energetics vacancies

short-range

un-

heat of formation

with negative

of magnetic

work

cannot help decide between these two investigations

realistically

irradiation.

an

open one, since recent work of Miinster and Sageldg)

the

the variation

system

order is at present

and

a conclusion can only be a tentative one. The same conclusion has been reached by Ryan et aZ.(l4) from

of

Cal/g atom-deg.

from

of Ni-Cu alloys, although

of

Ni-Au

of whether or not the Ni-Au

positive

the

entropy

behavior during ageing of the electrical resistivity of the Hall coefficient

exists,

The question

the

contribution

of about -0.7

25

NICKEL-GOLD

depend

pa,irwise bonding

kinds of pairs as these

and not on the energies in the

on the other hand, the sign and

of the AH,

values depend markedly

upon

of the pure components. REFERENCES

P. A. FLINN, B. L. AVERBACH and M. COHEN, Acta Met. 1, 664 (1953). L. L. SEICLE, M. COHEN and B. L. AVERBACH, J. Met&, N.Y. 4. 1320 (1952). R. A. BRIANI and ‘W. K. MURPHY, J. Phys. Chem. 62, 327 --- I19m\. R. A. ORIANI and W. K. MURPHY, Proceedings of the Symposium on Physical Chemistry of Metallic Solutions, National Physical Laboratory, Teddingt’on (1958). 5. 0. KUBASCHEWSKI, W. A. DENCH and V. GENTA, Proceerl\----I.

ings of the Symposium on Physical Chemistry of Metallic Solutions, National Physical Laboratory, Teddington (1958).

J. S. LL. LEACH 6. J. S. LL. LEACH. Private communication; and M. B. BEVER, Tmns. Amer. Inst. Min. (Metall.) Engrs. 215, 708 (1959). 7. J. L. MEIJERING. Private communica.tion. 8. R. P. RASTOGI and K. T. R. VERMA, Current Science, India 24, 336 (1955). 9* . L. S. NANIS. Master’s Thesis, Massachusetts Institute of Technology (1954). 10. J. PRATT. Private communication. of the Symposium on Physical 11. C. B. ALCOCK, Proceedings Chemistry of Metallic Solutions, National Physical Laboratory, Teddington (1958). 12. M. FUKUSIMA and S. MITUI, Sci. Rep. Tohoku Univ., Honda Anniv. Vol. 940 (1936). 13. W. K~STER and W. SCALE, 2. Met&l. 48, 592 (1957). 14. F. M. RYAN, E. W. PUGH and R. SMOL~CHO~SKI. Private communication; Bull. Amer. Phys. Sot. (March 1959). 15. R. A. ORIANI, Acta Met. 3, 232 (1955). 16. 0. KUBASCHEWSKI and J. A. CATTERALL, Thermochemical Data of Alloys. Pergamon Press, London (1956). V. GENTA, ref. 16, p. 50. W. DESORBO, Acta Met. 3, 227 (1955). A. M~;NSTER and K. SAGEL, Proceedings of the Symposium on Physical Chemistry qf Metallic Solutions. National Physical Laboratory, Teddington (1958).