Themes of the Day:

• Introduction to Phase Diagrams
• Applying the Phase Rule and Lever Rule
• Equilibrium Crystallization in Binary Systems

A Useful Web Resource on Phase Diagrams from Brock University

Introduction to Phase Diagrams

• What do they show? What are they useful for? How are they made?
• Phases (P) - physically seperable matter - solids: different mineral phases; liquids: e.g., vinegar and oil; gasses: air; fluids: supercritical H₂O
• Components (C) - Minimum number of chemical species required to describe the chemical variation in a system
• Degrees of Freedom (F) - How many variables (P,T,X) can be varied independently?
• (General) Phase Rule: F = C - P + 2

Applying the Phase Rule and Lever Rule

• Divariant, Univariant, and Invariant Systems
• One component, P-T variable system - SiO₂ F = C - P + 2
• Binary T-X system (Pressure constant) - An-Di F = C - P + 1
• Applying the Lever Rule - An-Di

Equilibrium Crystallization in Binary Systems

• (Simple) Eutectic System (with no solid solution): Diopside-Anorthite
• Peritectic System (incongruent melting) - Forsterite-SiO₂
• Complete Solid Solution System - Anorthite-Albite, Forsterite-Fayalite
• Partial Solid Solution System - Albite-Orthoclase - at differing pressures