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A eutectic reaction is one in which, upon cooling, a liquid transforms to two solid phases: L --> A + B

My textbook defines a congruent phase transformation as: "A transformation for which there is no change in composition for the phases involved".

The book gives eutectic reactions as an example of an incongruous phase transformation.

However, I do not understand why. If there is no solid phase present initially, how can the solid phase be considered to have changed composition?

Could anyone perhaps give me a clearer explanation of what a congruent reaction is? I have searched around but all references I can find give the same short sentence about composition.

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A congruent phase transformation is "A transformation that the initial phase and the final phase have the same composition", no matter the initial phase is the solid phase or the liquid phase.

source: Phase Diagrams in Metallurgy, written by Frederick N Rhines enter image description here

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  • $\begingroup$ can you cite your source please $\endgroup$
    – pentane
    Dec 24 '17 at 9:10

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