1 (506)

Prévia do material em texto

154 5 SIMPLEMIXTURES
5E Phase diagrams of ternary systems
Answers to discussion questions
D5E.2 �e lever rule, [5C.6–170], applies in a ternary system, but with an important
caveat. For binary systems the tie lines to which the rule appplies are always
horizontal and so can be added to the phase diagram at will. In contrast, for
a ternary system the tie lines have no such simple orientation and have to be
determined experimentally. �us the lever rule applies, but in order to use
it additional information is needed about the tie lines at the composition of
interest.
D5E.4 �e composition represented by point c is approximately xNi = 0.73, xFe = 0.20,
xCr = 0.07.�is is a three-phase region, with Fe, Ni and γFeNi present.
Solutions to exercises
E5E.1(b) �e ternary phase diagram is shown in Fig 5.27.
0.0
0.2
0.4
0.6
0.8
1.0
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
(i)
(ii)
(iii)
A
BC
xAxC
xB
Figure 5.27
E5E.2(b) �e composition by mass needs to be converted to mole fractions, which re-
quires the molar masses: MNaCl = 58.44 gmol−1, MH2O = 18.016 gmol−1, and
MNa2SO4 ⋅ 10 H2O = 322.20 gmol−1. Imagine that the solution contains 33 gNaCl,
33 g Na2SO4 ⋅ 10H2O and hence (100−33−33) = 34 g H2O.�e mole fraction
of NaCl is
xNaCl =
mNaCl/MNaCl
mNaCl/MNaCl +mNa2SO4 ⋅ 10 H2O/MNa2SO4 ⋅ 10 H2O +mH2O/MH2O
= (33 g)/(58.44 gmol−1)
(33 g)/(58.44 gmol−1) + (33 g)/(322.20 gmol−1) + (34 g)/(18.016 gmol−1)
= 0.22