Thermal evolution and mechanical properties of vitreous fibres in the SiO₂-Li₂O-TiO₂-Al₂O₃ system

Abstract

The thermal evolution of glass fibres of the SiO₂-Li₂O-TiO₂-Al₂O₃ system has been investigated by X-ray diffraction, DTA and SEM. Within the range of the compositions investigated (2 to 10 mol % TiO₂) SEM and SAXS measurements on bulk materials have shown that a small addition of Al₂O₃ (3 mol %) does not modify the limits of the immiscibility region present in the ternary system SiO₂-LiO₂-TiO₂. Within this region TiO₂-rich droplets are more than likely to be formed. As to tensile strength, the “asquenched” fibres of the composition placed within the immiscibility dome give higher values than that obtained outside the liquid-liquid region and these values are higher than those measured on E-glass fibres. A slight crystallization in all the fibres leads to a continuous decrease of the initial tensile strength. With regards to the crystal phases presented by the crystallized fibres, the first exothermic peak is due to the simultaneous crystallization ofβ-quartz (ss) and lithium disilicate whereas the second peak is due, most probably, to aβ-quartz (ss) →β-spodumene (ss) phase transformation as well as to the formation of Li₂TiSiO₅. The path of crystallization of the other detected Ti-compounds is similar to that proposed by Furukawa and White.