# Eutectic Point

Entry by Emily Redston

 www.tulane.edu/.../geol212/2compphasdiag.html Figure 1 shows a common and relatively simple binary phase diagram known as a eutectic phase diagram. A eutectic diagram can be thought of as the intersection of two solid solution diagrams. At the intersection of the two liquidus lines, the melt is in equilibrium with the two solid phases. In other words,a liquid phase is transformed into two solid phases upon cooling, and the opposite occurs upon heating. This is called a eutectic reaction, and can be written as $L \rightleftharpoons A + B$ According to Gibbs Phase Rule, we know that the number of degrees of freedom is $F=\left( C+2-P \right)=2+2-3=1$. Zero degrees of freedom means that we cannot have a solidification range, and thus the melt must solitify at exactly one point --- the eutectic point!

## References

[1] Spaepen, Frans. Applied Physics 282: Solids: Structure and Defects. Harvard University

[2] Haasen, Peter. Physical Metallurgy. Cambridge: Cambridge UP, 1996.

[3] Callister, William D. Materials Science and Engineering: an Introduction. New York: John Wiley & Sons, 2007.