Micron order structural inhomogeneities in vitreous silica observed by etching technique

Etching of various vitreous silica samples over a long period (∼ 200 min) with hydrofluoric acid revealed a high contrast configuration of micron to sub-millimeter order boundaries similar to the grain boundaries of crystalline materials. In order to better understand this new result, various parameters, such as the vitreous silica preparation processes, the type of basic insume, the grain size of silica powder, the surface roughness, and the OH-content, were studied. They should no correlation with the configuration of "amorphous-grain". A possibility of an anistropic micro-strain configuration induced by heterogeneous distribution of defects and impurities in the vitreous silica structure is suggested to explain the appearance of such grain boundary-like contrast.