Sol-gel alumina fibre mats for high-temperature applications

Polycrystalline, high-alumina fibre mats (with 4 wt.% SiO 2), for application as high-temperature thermal insulation materials having a web-like structure, were fabricated in situ by a single-step sol-gel spinning technique using a multi-orifice spinneret. Strong and resilient fibres with diameters in the range 3–10 μm were obtained from spinnable alumina–silica sols devoid of organics as the binder aid. Incorporation of 4 wt.% SiO 2 as an additive increased the stability of the metastable transition alumina phases, which helped to increase the strength of the fibre mats. The mats exhibited a small linear shrinkage of about 2.75% at 1600 °C. Disintegration of the mats was also found to be negligible (about 2.25 wt.%) at 1600 °C. The health hazard involved with airborne fibres was drastically minimised in the developed fibre mats by applying sol-gel coatings on their surfaces and subsequent calcination at 1200 °C. The oxide-coated fibres exhibited coherent coatings by anchoring loose surface fibres in a network of alumina.