The crystallization kinetics of Na2O · 3SiO2 have been determined over the temperature range between 600°C and 800°C. The (metastable) melting point of this material has been determined as 811 ± 3°C. The growth rate vs. temperature relation exhibits the maximum generally found for glass-forming systems, with the maximum growth rate (3.3 x 10-6 cm sec-1) observed at 735 °C. Under all conditions of growth, the crystal-liquid interfaces are faceted. This is indicative of significant growth rate anisotropy, and suggests that the entropy of fusion is large in Jackson's sense (ΔSfM &62- 4R, where ΔSfM is the molar entropy of fusion). Assuming ΔSfM = 4R, by analogy with the characteristics of Na2O · 2SiO2, the reduced growth rate versus undercooling relation has been constructed. The form of this relation - a straight line of positive slope passing through the origin - is suggestive of growth by a screw dislocation mechanism. The magnitudes of the growth rates are in close accord with the predictions of the standard model for such growth.
ASJC Scopus subject areas
- Condensed Matter Physics