Crystallization of Highly Supercooled Silicate Melts

Crystallization of liquids in the system CaO‐MgO‐Al₂O₃‐SiO₂ at one atmosphere has been studied at temperatures between the glass transition (T_g) and the solidus. To determine the textures, compositions and unit‐cell parameters of the crystalline phases, the authors have characterized the experimental charges over a wide range of length scales by scanning and transmission electron microscopy, electron microprobe analyses, X‐ray diffraction, and Raman spectroscopy. With increasing temperature, crystals tend to reach the equilibrium composition, but the relative importance of thermodynamic and kinetic factors is a single function of T‐T_g, regardless of liquid composition. This feature is of considerable practical interest as it provides the possibility, not only to predict, but also to control the composition of the crystallizing phases.