Effect of solid content on formation of sol–gel derived mullite fibres

Abstract

Continuous mullite fibres were prepared from dry spinning a sol prepared from aluminium nitrate, aluminium isopropoxide and tetraethylorthosilicate. By adjusting temperature, gelling degree could stabilise at a certain value and the sol–gel transition could be transferred to the spinning line. Continuous fibres could be formed from such spinnable sols immediately before complete gelling by controlling the spinning temperature and the various processing parameters. The samples were characterised by thermal gravity analysis/differential scanning calorimetry, scanning electron microscopy and X-ray diffraction. The results show that sintering of the precursor fibres from sols with solid content above 50% at 1100°C yields crack free mullite ceramic fibres. The calcined fibres were flexible with good handing characteristics and had smooth surfaces. Sintering of the precursor fibres at 1100°C yields complete crystal, which is a tetragonal metric like mullite.