On the Development of Two-Phase Structure in Glasses with Special Reference to the System Bao-SIO2

摘要

The technique of 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 process of phase separation was observed. At low BaO contents, the separation was characterized by the appearance of discrete, amorphous, second-phase particles. For compositions near the center of the miscibility gap, the separation process resulted in two continuously interconnected phases similar to those found in the corresponding bulk glasses. In the thinnest of these films the process was observed to proceed 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 the coalescence of discrete second-phase particles into an interconnected submicrostructure are discussed. It is suggested that coalescence may take place when either of these processes results in the particles approaching within some small distance of each other. The results indicate that observations of final phase-separated morphologies are inadequate for specifying the processes by which those morphologies arose. (Author)