Phase transformation

Japanese: 相変態 - そうへんたい（英語表記）phase transformation

The various states of a substance that have the same chemical composition but different physical properties and atomic arrangements are called transformations. For crystalline phases, the term allotrope is used to mean the same thing as polymorphism, and for transformations of simple substances, but for metallic elements, the term transformation is more commonly used. In particular, the change in the collective state of the same element that occurs when steel or alloys are heat-treated, that is, the transformation, is generally called a phase transformation. Iron has the allotropes α-iron, γ-iron, and δ-iron, and α-iron has a body-centered cubic lattice, but at approximately 910°C it changes to γ-iron with a face-centered cubic lattice.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

化学組成は同一であるが，物理的性質や原子配列が異なる物質のそれぞれの状態を変態という。結晶相では多形と同じ意味に，単体の変態には同素体という語が用いられるが，金属元素の場合には変態という語を用いることが多い。とくに鋼や合金を熱処理した場合に起こる同一元素の集合状態の異なる変化，つまり変態を一般に相変態と呼んでいる。鉄にはα鉄，γ鉄，δ鉄という同素体があって，α鉄は体心立方格子であるが，約910℃で面心立方格子のγ鉄に変わる。

出典　株式会社平凡社世界大百科事典第２版について　情報

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