Novel colloidal silica technology for MgO-containing refractories – Part 1: Anti-hydroxylation binder

Refractory castables play major roles in high-temperature applications and two important types are MgO-containing and colloidal silica-bonded castables. Whereas the former shows high refractoriness and resistance to slag corrosion, the latter offers straightforward mixing, curing, and drying processes. However, their association in a same system has not been synergistic. During mixing, MgO particles release Mg2+ions that trigger the gelling of colloidal silica. Therefore, small MgO additions gradually hard high-alumina colloidal silica-bonded castables; conversely, larger amounts instantly set the system, hindering homogenization and casting. Despite the challenges, there is potential for making these systems compatible towards technological application. This study successfully combined fine MgO sinter with a novel aqueous dispersion of epoxysilane-modified colloidal silica, creating self-flowing suspensions of good workability. Cured samples exhibited no signs of damage by MgO hydroxylation, sufficient strength for demolding and safer drying. Thermal treatments resulted in a dense microstructure with MgO grains surrounded by Mg2SiO4.