# Lecture 24: Building Binary Phase Diagrams, Part II | Summary and Q&A

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October 23, 2023
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MIT OpenCourseWare
Lecture 24: Building Binary Phase Diagrams, Part II

## TL;DR

This content discusses binary phase diagrams, focusing on peritectic reactions, intermediate phases, and the use of Thermo-Calc software for analysis.

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### Q: What is a peritectic reaction?

A peritectic reaction is a transformation that involves a liquid and a solid at high temperatures, resulting in the formation of a solid. This reaction is characterized by a peritectic point on the phase diagram.

### Q: Can you provide an example of a peritectic reaction?

In the copper-zinc system, there is a peritectic reaction between pure copper and a solid solution of copper with zinc, resulting in the formation of a different solid phase. This can be observed on the phase diagram as a peritectic point.

### Q: What are intermediate phases?

Intermediate phases are phases that are stable for some intermediate compositions but do not exist in the pure component cases. They represent structurally distinct phases that form when two components are combined in specific proportions.

### Q: How is Thermo-Calc software used in the analysis of binary phase diagrams?

Thermo-Calc software is used to calculate equilibrium properties of binary systems and generate phase diagrams. It allows for the analysis of free energy composition diagrams and the identification of different phases present in the system.

## Summary & Key Takeaways

• The professor discusses peritectic reactions, which involve a liquid and a solid transforming into a solid at high temperatures.

• Examples of peritectic reactions in the copper-zinc system are explored, highlighting the presence of peritectic points on the phase diagram.

• The concept of intermediate phases is introduced, referring to phases that are stable for intermediate compositions, but not for pure components.

• The Thermo-Calc software is used to analyze the iron-chromium phase diagram, showing the existence of an intermediate phase and illustrating the construction of free energy composition diagrams.