E: eutectic

1
Reaction Scheme Ce-Cu-Pu
E eutectic P peritectic U all of the above
being invariant pts
2
dissociating binary compounds a) upper Temp limit
of stability (stable compound Tmax)
invariant pts are E1 E2 what about R ? at R,
LAB ? AB (p4), but not the final
solidification pt because AB exists on the binary
side
3

• 1) X ? ?A-C-AB (finally at E1)
• L ? LA ? (along XE1) LAAB ? A being
  resorbed but not completely ? (at E1)
  LAAB? ACAB
• 2) Y ? ?C-B-AB (finally at E2)
• L ? LA ? (along e2R) LAB ? at R, where
  to go, E1 or E2 ?
• due to geometrical and thermodynamic reasons,
  proceeding from R to E1 LAB ? LAAB, along
  RE1 A is being resorbed and completely at X (on
  RE1) ? LAB ? (at l on mE2) LABC ? (at E2)
  LABC? ABCB
• check pt what about the cooling path of the comp
  Z ?

Y
excluding Y
including Y
4
3) V ? ?C-B-AB (finally at E2) L ? LA ?
(along e2R) LAB ? (along RE2) LABB ? (at E2)
CBAB due the same reason of the case Y,
Liq cannot move from R to E1 4) K ? ?C-B-AB
(finally at E2) L ? LAB ? (along l E2)
LABC ? (at E2) ABCB 5) W ? on a C-AB join,
also on the boundary line btw AL and ABL
?
?
?
along ? ? no way ? the phase field is AB but W is
off L-AB along ? ? yes ? the phase field is AB
and the corresponding solid is AB along ? ? no
way ? W is outside the L-A-AB ? along ? then LAB
? ABC at m ? all the comp pts on C-AB finally
solidify at and the phase is
5

• b) lower limit stability stable compound
  Tmin

all the solidification path terminate at E at R
A, B, AB, L participate in equil, ? f0 at E
A, B, C, L participate in equil ? f0
6

• in considering a ternary compound, ABC
• a) congruently melting ABC (comp of ABC inside
  the ABC primary phase field)

C
? A-ABC-C E1 ? B-ABC-A E2 ? C-ABC-B E3
for the polymorphic phase transformation of ABC
ABC
A
B
7
when a binary compound (AB) and a ternary
compound (ABC) coexist
phase tansf of ABC
phase transf of AB
8

• b) melting ternary compound
  (comp of ABC outside the ABC primary phase field)

C
? A-C-ABC P1 ? C-B-ABC E ? B-A-ABC P2
in cooling the comp of ABC, the first solid to
appear is not ABC but A in this case L ? LA ?
at m, LA ? ABC (100)
e1
C
X L ? (at TX) LA ? (along XX) LAABC ? (on
XX) LABC ? (along XE) LABCC ? (at
E) ABCCB
P1
X
E
e3
X
ABC
X
X
A
m
ABC
B
P2
A
B
e2
9
? A-C-ABC P1 ? C-B-ABC E ? B-A-ABC P2
C
Y L ? (at TY) LA ? (along YY) LAABC ?
(on YY) LABC ? (along YE) LABCB ? (at
E) ABCBC
e1
C
P1
E
e3
ABC
A
m
Y
Y
ABC
Y
B
Y
P2
B
A
e2
10
? A-C-ABC P1 ? C-B-ABC E ? B-A-ABC P2
C
Z ? ? A-C-ABC (at P1) L ? LA ? (along mP1)
LAABC ? (at P1) ACABC
e1
C
P1
E
e3
ABC
Z
A
m
ABC
B
P2
B
A
e2
11
double incongruency in cooling the comp of ABC
L ? LA ? (at K) LAC ? (finally at P) LAC ?
ABC namely, two different solids (crystals)
show up before precipitating ABC check pts try
cooling paths of comps X, K, Y
C
P ? A-C-ABC E1 ? C-B-ABC E2 ? B-A-ABC
ABC
B
A