Unary and Binary Phase Diagrams

1
Unary and Binary Phase Diagrams

• GLY 4200
• Fall, 2009

2
Unary Diagrams

• Unary diagrams have a single component
• We therefore usually choose to plot both P
  (pressure) and T (temperature) since composition
  is not a variable
• Examples
• Water
• Silica
• Carbon

3
Phase Rule for Unary Systems

• f c - p 2 1- p 2 3 - p
• If one phase is present, there are two degrees of
  freedom (both T and P)
• If two phases are present, there is one degree of
  freedom (either T or P)
• If three phases are present, there are no degrees
  of freedom

4
H2O Diagram
5
Terminology
6
Water ice
7
Silica Phase Diagram
8
Snowflake Obsidian

• The white patches are crystals of cristobolite,
  formed at high temperature
• The magma-crystal mix then erupted, chilling the
  magma and forming a volcanic glass matrix around
  the metastable cristobolite, which cooled too
  quickly to revert to tridymite

9
Carbon Phase Diagram
10
Climate Change Application

• Greenhouse Warming on Terrestrial Planets