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 Chem 263 Winter 2015
Problem Set #3
Due: Mar 6
1. Sketch the phase diagram of the NiO-Al2O3 system from 1500-2200 °C using
the following information. NiO melts at 1985 °C. Al2O3 melts at 2070 °C. There is a
single compound, NiAl2O4, that melts congruently at 2100 °C. Eutectics occur at
two points: 15% Al2O3, 1875 °C and 90% Al2O3, 1980 °C. NiO forms a solid solution
with a maximum Al2O3 content of 5%. The nickel spinel also forms a solid solution
for Al-rich compositions up to 35% NiO, 65% Al2O3, but no solid solution forms for
Ni-rich compositions.
2. Sketch a phase diagram for a system A-B that has the following features. Three
binary compounds are present, A4B, AB, and AB3. A4B melts incongruently to give A
plus liquid. AB melts congruently. AB3 has an upper limit of stability.
3. For the phase diagram shown in West Ch. 7, Figure 7.16, describe the reactions
that would be expected to occur upon equilibrium cooling of a melt of composition
48% A and 52% B. How might the product differ if the melt is cooled rapidly?
4. Construct a triangular grid for representing three-component phase diagrams.
Let the three components be Na2O, CaO, and SiO2. Mark on your triangle, using a
mole% scale, the compositions of the following phases: Na2SiO3, Na2Si2O5, CaSiO3,
Ca3Si2O7, Ca2SiO4, Ca3SiO5, Na2CaSiO4, Na2Ca3Si6O16, Na2Ca2Si3O9, Na4CaSi3O9,
Na2CaSi5O12.
5. a) Label each of the fields in the following simplified phase diagram, except the
tiny one on the right.
b) Use the Phase Rule to determine the degrees of freedom at points L, P and E.
c) Envision this system as a slowly cooling magma chamber. Start with a liquid of
bulk composition d. In the circles below, show schematically the appearance of the
system at temperatures T3 + 0.01°C, T3 - 0.01°C, T4 and T5. When drawing, think
about the crystallization process, not just the numbers! Also, try to portray the
proportions of phases somewhat correctly. In the blanks, list the phases present,
and the amount & composition of each. Not every text line will be needed.
d) Given a solid of composition Mg2Si2O6, at what temperature will the solid first
melt? What will be the product(s) of melting? What are their compositions?