Raman Study of the Interface between Hot-Pressed Silica Parts

We present a Raman spectroscopy study of silica glasses prepared by hot‐pressing of gels. Our particular interest is the structure at the interfaces formed during hot‐pressing of small parts to obtain large pieces, such as silica tubes for optical‐fiber preforms. A specific feature of the interface that distinguishes this layer from the bulk is its fractal structure. The parameters of the fractal units, including their maximum dimensions in real space, are determined by the pre‐hot‐pressing mechanical processing. We attribute this structure to residual microcracks inherent in the surface layer of polished plates. There are no fractals at the interfaces sintered at temperatures higher than the glass transition temperature.