The growth of calcium metasilicate polymorphs from supercooled melts and glasses

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Abstract
Summary: The morphology of calcium metasilicate produced during the crystallization of glasses and melts of approximately metasilicate composition has been investigated. Both isothermal heat treatments and a dynamic crystal-pulling technique were employed. The crystallization took place by a dendritic or spherulitic mechanism, according to which of the crystal polymorphs is stable under the prevailing conditions. The morphology of the crystals is controlled by the ease with which the anionic groups present in the amorphous phase can be incorporated into the growing crystals. This is reflected in the values of the activation energies of crystal growth found for α-CaSiO3 (160 kJ mol−1) and for β-CaSiO3 (319 to 383 kJ mol−1). The Keith and Padden theory of spherulitic crystallization was verified for the growth of β-CaSiO3 over a range of supercoolings. Time-temperature-transformation diagrams have been constructed from the experimental data.
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