Internal Nucleation of Highly Undercooled Magnesium Metasilicate Melts

Reid F. Cooper, Wooyoung Yoon, John H. Perepezko

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Abstract

Crystallization and vitrification in undercooled, fine magnesium silicate droplets, with compositions ranging from 34.5 ≤ wt% MgO ≤ 39.9, were examined following containerless drop tube processing. From an initial phase assemblage of a mixture of the metasilicate (MgSiO3) polymorphs orthoenstatite and clinoenstatite, three morphological powder types were observed following processing: unmelted shards, glass spheres, and melted/recrystallized spheres. The primary phase in the powders processed at a maximum temperature of ∼1650°C is the high‐temperature metasilicate polymorph protoenstatite, with metastable forsterite (Mg2SiO4) also appearing. The melted/recrystallized spheres have the uniform, submicrometer texture of a glass ceramic, decisively different from the surface crystallization textures normally seen for melts/glasses of these compositions. Transmission electron microscopy results indicate that the glass‐ceramic texture occurs because the process technique allows a liquid‐phase immiscibility to precede crystallization. The phases and textures developed during containerless solidification processing of these metsilicate compositions are analyzed thermodynamically; the minimum amount of undercooling required for amorphous phase separation is evaluated using the metastable extensions of the forsterite + liquid and the silica‐rich, twoliquid miscibility phase boundaries. The application of metastable phase diagram analysis is demonstrated as an effective guide for identifying potential compositions for development of novel glass‐ceramics.

Original languageEnglish
Pages (from-to)1312-1319
Number of pages8
JournalJournal of the American Ceramic Society
Volume74
Issue number6
DOIs
Publication statusPublished - 1991
Externally publishedYes

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Keywords

  • crystallization
  • glass‐ceramics
  • melts
  • nucleation
  • phase separation

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry

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