eutektinen

Eutektinen, in Finnish, corresponds to the term eutectic in materials science. It describes a special composition in a multi-component system that has the lowest melting point of all mixtures in that system, and that solidifies from liquid at a single temperature into a mixture of two or more solid phases.

On a binary phase diagram, the eutectic point is where the liquidus lines converge at the minimum melting temperature. At the eutectic temperature, a liquid solution can transform directly into two solid phases simultaneously, expressed as L → α + β. The resulting microstructure is typically a fine lamellar or rod-like mixture of the two solids.

Eutectic compositions are found in many metal systems and in some alloy systems. Notable examples include the tin–lead (Sn–Pb) solder, which has a eutectic composition around 61.9% tin and 38.1% lead with a melting point of about 183°C; the aluminum–silicon (Al–Si) system has a eutectic near 12.6 wt% silicon and a eutectic temperature around 577–580°C; and in iron–carbon (Fe–C), a eutectic occurs at about 4.3 wt% carbon and roughly 1147°C, producing cementite and austenite upon solidification. A broader, non-metal example is the NaCl–H2O system, which has a eutectic composition near 23.3 wt% NaCl and a eutectic temperature around −21°C.

Eutectic structures influence properties such as melting behavior, castability, machinability, and mechanical performance. Understanding eutectic points aids alloy design, soldering practices, and casting processes.