Experimental and Calculated Ag + Au + Ge Phase Diagram

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I.

BIBLIOGRAPHIC SURVEY

THIS survey deals only with the phase equilibrium temperatures of the binary alloys Ag + Au, Ag + Ge, Au + Ge and of the ternary alloys Ag + Au + Ge; the values relating to the necessary thermodynamic functions will be examined in Section IV. A. Ag + Au System Both metals have a similar crystal structure (fcc) and can be mixed in any proportion in the solid and liquid states as well. Jaenecke, 4 Raydt, 5 Wagner, 6 White, 7'8 Markali, 9 Cooke, 1~ and Miane 11 contributed to establish the equilibrium phase diagram. The liquidus and solidus lines are very close together since they are only 1.7 K apart at XAu = 0.59']~ (Figure l(a)). Wagner6 estimated from a calculation this temperature difference to be 1.3 K. In spite of many contradictory papers about the solid phase,t2-22 it seems that continuous solid solutions do exist above 650 K.

in the solid state; Tables I and II compile these values. Moreover, in the solid state, the solubility of silver is considered as negligible. C. Au + Ge System This binary alloy exhibits a deep eutectic ]2'13'14 which is shifted toward the gold-rich side (see Table I and Figure l(c)). In 1984 Okamoto and Massalski 29 compiled all the thermodynamic values of this binary system. Informa-

T

Ag.Au 1320"

%

B. Ag + Ge System The equilibrium phase diagram of this alloy exhibits a deep eutectic which is shifted toward the silver-rich region (Figure l(b)). Phase equilibrium temperatures and structural parameters of this binary system have been gathered by Hansen, ]4 Shunk, ~3 and Elliott. ~2 Recently Okamoto and Massalski23 published a provisional compilation of the thermodynamic properties and equilibrium temperatures of this system. From these compilations we kept the coordinates of the eutectic point and the values of the solubility of germanium

S. HASSAM, Maitre-Assistant, and M. GAMBINO, Maitre de Conference, are with Universit6 de Provence, Place V. Hugo 13331, Marseille Cedex 3, France. M. GAUNE-ESCARD, Directeur de Recherche, and J. P. BROS, Professeur, are with Syst~mes Energrtiques et Transferts Tbermiques, Centre de Saint-Jrrrme, Rue H. Poincarr, 13397 Marseille Cedex 13, France. J. AGREN is Research Associate, Division of Physical Metallurgy, Royal Institute of Technology, S-100 44 Stockholm, Sweden. Manuscript submitted December 15, 1986. METALLURGICALTRANSACTIONSA

12B0" O

S

1240~234

XAu ~_~

0

015 (.)

Fig. 1--(a) Equilibrium phase diagram of the Ag + Au system. Liquidus: A;4 .k;5 0;6 A;7 __;~2 + . , Solidus: ~.;4 0;5 Q;6 [S];7 ___;J2 V.4, VOLUME 19A, MARCH 1988--409

!I

Table I. Coordinates of the Ag + Ge and Au + Ge Eutectic Points

,o.o.

Ag + Ge

234 1210,

12OO

I000

\

o

Xce

T/K

0.260 0.241 0.239 0.239

923 922 924 --

Au + Ge

X~e

T/K

0.240 0.270 -0.280 0.270 0.280 *according to Malmejac (see Reference 26)

632 629 636 630 637 635

Ref. 24 25 26 *

Ref. 30 31 32 33 34 35

Table II. Solubilities of Germanium in Silver and Gold in the Solid State

80(:}

Ag + Ge

XG~ t 0

0,5

(b)

Xce

T/K

0.0650 0.0800 0.0810 0.096* 0.0792 0.0567

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