
Metals 1.10 Noble Metals and Noble Metal Alloys 333
Table 3.1-119 Molar heat capacities of solid Ag and Au,
c
p
= 4.1868 (a +10
−3
bT +10
−5
T
−2
)J/K [1.222, p. 219]
Element a b c Temperature
range (K)
Ag 5.09 2.04 0.36 298–mp
∗
Au 5.66 1.24 – 298–mp
∗
∗
= melting point
Table 3.1-120 Latent heat and temperatures of transition of
Ag and Au intermediate compounds [1.222, p. 189]
Phase N
2
Transition T
t
L
t
β-AgCd 50 β
–β 211 712
AgZn 50 order–disorder 258 2449
AuCu 50 order–disorder 408 1779
AuCu
3
75 order–disorder 390 1214
AuSb
2
66.7 β–γ 355 335
T
t
= transition temperature, L
t
= latent heat of transition,
N
2
= mole fraction of the second component
Table 3.1-121 Latent heats and temperatures of fusion of
Ag and Au intermediate compounds [1.222, p. 188]
Phase N
2
T
m
(
◦
C) L
m
(hJ/g-at.)
β-AgCd 67.5 592 8.46 0.42
γ -AgZn 61.8 664 7.79 0.33
AgZn 72.1 632 8.75 0.42
δ-AuCd 50.0 627 8.96 0.50
AuSn 50.0 418 12.81 0.33
β-AuZn 50.0 760 12.31 0.54
N
2
= mole fraction of the second component, T
m
= melting
point, L
m
= Latent heat of fusion.
For compositions and crystal structures, see
Tables 3.1-122–3.1-124 [1.217, 218, 223,224]. Primary
solid solutions have the fcc structure of Ag and the lat-
tice parameters correspond roughly to Vegard’s rule with
a few exceptions. Alloys with Pt, In, Mg, Cd, and Zn
form superlattice phases with tetrahedral and rhombo-
Table 3.1-118 Thermodynamic data of Ag [1.217, p. 107]
T c
p
H S G p
(K)
(J/K mol) (J/K mol) (J/mol) (J/mol) (at)
298.15 25.397 42.551 0 −12.687 1.09 × 10
−43
400 25.812 50.069 2.606 −17.421 5.02 ×10
−31
800 28.279 68.661 13.392 −41.537 1.45×10
−12
T = Temperature, c
p
= specific heat capacity, S = Entropy,
H = Enthalpy, G = free Enthalpy,
p = partial pressure of the pure elements
Cu
Ag
Zn
20 40 60 80
20
40
60
80 20
40
60
80
(at. %)
α(Cu-Zn)
α(Ag-Zn)
β
γ
ε
δ
η
a
b
c
Fig. 3.1-198 Ternary phase diagram: Ag
−
Cu
−
Zn [1.220, p. 153]
hedral symmetry. A characteristic series of structures
of intermetallic phases are formed with B-metals at
compositions corresponding to e/a values (valence elec-
trons per atom) of 3/2, 21/13, and 7/4 (Hume-Rothery
phases) [1.225].
Part 3 1.10