The bonding phases of refractory castables play a central role in their performance. Especially their behaviour at high temperature is decisively responsible for the performance of a refractory lining. While calcium aluminate cements have established themselves as "workhorse" for refractory castables (reliable and cost-effective), they nonetheless have some drawbacks (high risk of explosive spalling during drying, limited resistance to acidic slags and ashes) and, after years of optimization, only limited potential left for further improvements. By contrast, sols bonded castables experience a growing use in the industry (silica sols) and, despite their current limitations (low green strength, limited refractoriness), have much to offer. Especially alternative sols such mullite and spinel sols are starting to draw attention in order to improve the refractoriness and resistance to corrosion of sols bonded castables, but studies regarding their performance at high temperature are extremely sparse.
The thermomechanical and thermochemical behaviour of silica and spinel sols bonded high alumina refractory castables was investigated using wedge splitting measurements, high temperature thermal shocks and induction furnace tests. Silica sol bonded high alumina refractory castables are rather weak when compared to cement bonded high alumina refractory castables, but displayed an improved resistance to high temperature thermal shocks. The use of spinel sols improved greatly the high temperature mechanical and fracture resistance of the sol bonded high alumina refractory castables without degrading their resistance to thermal shocks and even slightly improving their resistance to corrosion.