Mullite fibre mats by a sol-gel spinning technique

Fine grained, microcrystalline mullite (Al4+2xSi2-2xO10-x) fibre mats with a web-like structure were fabricated by a sol-gel spinning technique using a multi-orifice spinneret. Points of contact in gel fibre mats helped in the formation of a web-like fibrous body having reasonable strength and very little dust formation after calcination. Strong and resilient fibres with diameters in the range 3-12 mum were obtained by a single-step sol-gel method from spinnable sols devoid of organics as the binder aid. Crystallization of gamma-alumina and mullite at about 900degreesC and 1250degreesC, respectively was confirmed by differential thermal analysis (DTA) and X-ray diffraction (XRD). Thermogravimetry (TG) indicated the removal of most of the volatiles at about 500degreesC accompanied by a weight loss of about 48%. Scanning electron microscopy (SEM) shows the presence of small grains (80-150 nm in size) in the fibres calcined at 1250degreesC. Fourier transformed infrared spectroscopy (FTIR) indicated the sequence of transformations taking place during heat-treatment of gel fibres at different temperatures. The individual fibres in the mats calcined at 1250degreesC exhibited a tensile strength of 1300-1600 MPa.