Phase Separation in Borosilicate Glasses as Seen by Electron Microscopy and Scanning Electron Microscopy

Microstructures of two sodium borosilicate glasses were examined. Electron micrographs of replicas of water‐etched fracture surfaces show that the microphases increase in size with the temperature and time of heat treatment. The relative amounts of soluble and insoluble microphases remain essentially unchanged. Scanning electron micrographs of completely leached glasses show that the insoluble phase is randomly interconnected. Scanning electron micrographs of colloidal deposits in the pores of the leached glass, which result from acid leaching of the heat‐treated base glass, are shown. Electron micrographs showing re‐solution of the phases are also included.