Premium
Internal Nucleation of Highly Undercooled Magnesium Metasilicate Melts
Author(s) -
Cooper Reid F.,
Yoon Woo Young,
Perepezko John H.
Publication year - 1991
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1991.tb04104.x
Subject(s) - materials science , crystallization , supercooling , nucleation , forsterite , texture (cosmology) , phase (matter) , ceramic , mineralogy , chemical engineering , glass ceramic , metastability , metallurgy , thermodynamics , chemistry , physics , organic chemistry , artificial intelligence , computer science , engineering , image (mathematics)
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 (MgSiO 3 ) 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 (Mg 2 SiO 4 ) 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.