Phase Separation in the System BaO‐SiO2

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Abstract
A simple, rapid‐quenching device was used to investigate the extent of liquid‐liquid immiscibility in the system BaO‐SiO2. A metastable miscibility gap was found with an upper consolute point at about 10 mole % BaO and 146OOC. Bulk glass samples of different compositions and heat treatments were examined by direct‐transmission electron microscopy to determine the phase separation morphology. At low BaO contents the separation was characterized by spherical barium‐rich particles in a silica‐rich matrix. For compositions near the center of the gap, the structure consisted of two phases continuously interconnected throughout the bulk of the glass. At higher BaO contents, spherical silica‐rich particles were found in a barium‐rich matrix. The dependence of the morphology on quench rate and heat treatment was investigated. Predictions of other authors concerning the occurrence of BaO‐SiO2 immiscibility are compared with the present results.

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