eutectic: a standalone construct

Frederick Guthrie coined the term in his 1884 paper On eutexia in The Philosophical Magazine, from the Greek for easily melted, to name a mixture whose components, blended in one particular ratio, melt and freeze at a single fixed temperature that is lower than the melting point of either pure component on its own. That special ratio is the eutectic composition and the shared temperature is the eutectic point: at it the liquid solidifies directly into a fine, interlocked mixture of the two solid phases at the same instant, instead of one component crystallising out first. Kenneth Jackson and John Hunt's 1966 analysis of lamellar and rod eutectic growth gave the modern quantitative account of how those two solids grow side by side out of the cooling liquid, tying the spacing of the resulting microstructure to how fast the mixture freezes. The construct is distinctive because it marks a single fixed point on a phase diagram, the chart that maps which solid or liquid states a mixture takes at each composition and temperature: the one composition and temperature at which a liquid and two solids can coexist together, which is why the eutectic serves as a reference landmark for designing solders and casting alloys, reading how rocks and minerals form, and lowering melting points in pharmacy and food science.[1][2]

Unit

A paired composition and temperature on a phase diagram at which a liquid freezes into two solid phases simultaneously

Recovery means

Not applicable

Measured by

Located experimentally by thermal analysis such as differential scanning calorimetry and cooling curves, and by mapping the phase diagram to find the lowest-melting composition