Sol–gel mullite as the self-bonding material for refractory applications

The physico-chemical properties of permanent binders used in refractories play a vital role in deciding high temperature mechanical properties. The presence of a glassy phase in the matrix of the refractory may not affect the low temperature properties significantly, however the high temperature properties are very much reduced. In the present study, the mullite precursor derived from the sol–gel route has been used as the self-bonding material to the fused mullite aggregates. The sol–gel mullite as the permanent binder yields density up to 2.48 g/cc. The room temperature flexural strength (172 kg/cm2) and compressive strength (785 kg/cm2) of the self-bonded fused mullite are comparable to that of the conventional clay/alumina bonded mullite products. However, superior high temperature mechanical properties such as Hot Modulus of Rupture (HMOR) (48 kg/cm2 at 1300°C), the retention flexural strength of 116 kg/cm2 after 10 thermal cycles of ΔT=1000°C and Refractoriness under load (RUL) (>1800°C) were obtained for the samples of fused mullite bonded by sol–gel mullite.