Micron order structural inhomogeneities in vitreous silica observed by etching technique

Etching of various vitreous silica samples over a long period (similar to 2 000 min) with hydrofluoric acid revealed a high contrast configuration of m icron to sub-millimeter order boundaries similar to the grain boundaries of crystalline materials. In order to better understand this new result, vari ous parameters, such as the vitreous silica preparation processes, the type of basic insume, the grain size of silica powder, the surface roughness, a nd the OH-content, were studied. They showed no correlation with the config uration of "amorphous-grain". A possibility of an anisotropic micro-strain configuration induced by heterogeneous distribution of defects and impuriti es in the vitreous silica structure is suggested to explain the appearance of such grain boundary-like contrast.