High-alumina refractory castables bonded with novel alumina-silica-based powdered binders

In recent years, nano-binders (mainly colloidal suspensions) have been proposed as alternative materials for applications that require CaO-free refractory lining or improved mechanical behavior at intermediate temperatures (700 °C< T < 1200 °C). Despite the benefits of these suspensions, nano-bonded castables usually present limited green mechanical strength and different on site logistics to handle the liquid. Considering the availability of novel alumina-silica-based powdered binders, this work investigated the role of submicron alumina and SioxX®-Zero (both supplied by Elkem company) on rheological and mechanical properties of vibratable high-alumina castables, aiming to identify whether they can be suitable options to replace colloidal silica suspensions. Cold and hot mechanical strength and apparent porosity in the range of 110-1400 °C, cyclic thermal shock resistance, creep tests and hot elastic modulus of the designed formulations were evaluated. According to the results, SioxX®-Zero-bonded compositions presented good flowability levels and their sintering process started around 800 °C. Adding boron carbide to the same formulations resulted in transient liquid sintering of the silica-containing refractories, which allowed the development of compositions with improved thermo-mechanical performance in the 600-1400 °C temperature range. Furthermore, the submicron alumina-bonded samples presented fast sintering, resulting in E values close to 200 GPa (the highest value so far registered in our lab for a coarse grain size formulation) after one heating-cooling thermal-cycle up to 1400 °C.