A silica-rich surface layer of Fe3+-containing aluminosilicate glass fibres is created by means of an inward diffusion process of divalent network modifying cations. The latter is caused by the reduction of Fe3+ to Fe2+ when the fibres undergo a heat treatment at temperatures around the glass transition temperature (Tg) in a reducing H2/N2 atmosphere. The thickness of the surface layer can be adjusted by varying the temperature or the duration of the heat treatment. The reduction process has a significant impact on the glass transition and crystallization behaviour, high temperature stability (HTS), and chemical durability of the fibres. The reduction deteriorates the HTS of the fibres in argon due to the decrease of Tg and increase of the crystallization temperatures. However, the crystallization behaviour and HTS in air are not affected by the reduction. This is because a re-oxidation of Fe2+` to Fe3+ occurs during the heating process in air. The formation of the silica-rich surface layer enhances the chemical durability of the fibres.
|Journal||Physics and Chemistry of Glasses-European Journal of Glass Science and Technology Part B|
|Publication status||Published - 2010|