Eutectic point - eutectic point

In a solid-liquid equilibrium system of two or more components, the temperature at which each component simultaneously precipitates from the melt, or conversely, the temperature at which the solid crystals of each component simultaneously melt. In the case where two components A and B do not form a solid solution, generally, when component B is dissolved in a liquid of pure component A, the freezing point drops, and pure component A crystals precipitate during solidification. The same is true for component B. At a certain composition, the freezing point of this two-component liquid mixture is at its lowest, and crystals of components A and B precipitate simultaneously. In this case, the system is two-component, three-phase, so if the pressure is constant, it becomes an invariant system according to the phase rule, and the temperature remains constant until solidification is complete as long as the three phases coexist. The precipitated solid phases of both components are an intimate mixture of crystals of A and B, and are called a eutectic mixture or eutectic. In a ternary system, a system in which one liquid phase and two solid phases coexist is a univariant system, so the eutectic point of the above pair of two components decreases with the increase in the third component, and eventually reaches a ternary eutectic point, which is lower than any of the binary eutectic points. [See other terms] Melting point diagram

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

二成分系以上の固液平衡において，各成分が融液から同時に析出する温度，逆にいえば，各成分の固体結晶が同時に融解する温度．二成分AとBとが固溶体をつくらない場合は，一般に純成分Aの液体にほかの成分Bを溶かすと凝固点は低下し，凝固のとき純成分Aの結晶を析出する．成分Bについても同様である．そして，ある特定の組成のとき，この二成分混合液体の凝固点は最低となり，成分AとBの結晶を同時に析出する．この場合，系は二成分三相となるから，圧力を一定とすれば相律により不変系となり，三相が共存するかぎり凝固が完了するまで温度は一定である．析出した両成分の固相はA，Bの結晶の緊密な混合物であり，共融混合物または共晶という．三成分系では一液相二固相の共存する系は一変系であるから，上記の一対の二成分の共融点は第三成分の増加とともに低下し，ついにはどの二元共融点よりも低い三元共融点に達する．[別用語参照]融点図

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