Electron Micrographs of Some Borosilicate Glasses and Their Internal Structure

Many electron micrographs were obtained for borosilicate glass which had been subjected to chemical attack after heat-treatment at various temperatures and durations in order to study changes in internal structure, the so-called "phase separation." Both replica and direct-transmission methods were applied to Vycor-type glass. The two kinds of picture showed good agreement with each other. The conclusions obtained are as follows: (1) So-called quenched-state glass contains a glassy microphase of alkali borate, with dimensions less than 100 a.u., which corresponds to the so-called low-melting component; (2) the longer the heat-treatment time under constant temperature the larger the size of this glassy microphase becomes; (3) another kind of glassy microphase (SiO₂-rich) which corresponds to the so-called high-melting component is also enlarged with increasing heat-treatment time; (4) the size of both glassy microphases shows different values with different heat-treatment temperatures. Based on the experimental results described, a discussion of the relation between the internal structure and some physical properties of the glass is presented.