Development of Two‐Phase Structure in Glasses, with Special Reference to the System BaO‐SiO2


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Vapor deposition was used to obtain homogeneous glass films of several BaO‐SiO2 compositions in the region of the metastable miscibility gap. The films were electron‐beam heated in the electron microscope, and the phase separation process was observed. At low BaO contents, separation was characterized by the appearance of discrete, amorphous, second‐phase particles. For compositions near the center of the miscibility gap, separation resulted in two continuously interconnected phases similar to those in the corresponding bulk glasses. In the thinnest of these films, the process proceeded by the coalescence of isolated particles into the interconnected second‐phase submicrostructure. At high BaO contents, rapid crystallization of the films prevented study of the separation process. Two processes which could lead to coalescence of discrete second‐phase particles into an interconnected submicrostructure are discussed. It is suggested that coalescence may occur when either of these processes results in the particles approaching within some small distance of each other. It is indicated that under appropriate conditions, this requirement may be satisfied by either process. These conclusions, together with the present observations of BaO‐SO2 thin films and those previously reported for bulk samples, indicate that observations of final phase‐separated morphologies are inadequate for specifying the processes by which those morphologies arose.

Original languageEnglish (US)
Pages (from-to)634-642
Number of pages9
JournalJournal of the American Ceramic Society
Issue number11
StatePublished - Nov 1968

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry


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