Novel silanized colloidal silica-MgO self-flowing dispersions with improved hydroxylation resistance

Abstract

MgO-containing and colloidal silica-bonded are important classes of refractory castables of, respectively, high refractoriness and straightforward processing. On the other hand, their combination is not synergetic. Although 0.1–1 wt% additions of MgO set and harden typical colloidal silica-bonded castables in a 1-hour time frame, greater amounts gel the system instantaneously. This paper addresses the combination of fine MgO sinter with a novel aqueous dispersion of colloidal silica whose particles’ surfaces were modified with an epoxysilane-based coupling agent. Their low reactivity produced self-flowing MgO-colloidal silica suspensions of excellent workability and, after curing, generated a packed magnesium silicate hydroxide hydrate (Mg5Si8O20(OH)2.8H2O) protective coating over MgO particles, hindering their hydroxylation and preventing volumetric expansion. The cast structures attained displayed safer drying and suitable strength. During thermal treatment, silica particles softened and promoted viscous flow, favoring grains densification. Therefore, after sintering, the microstructure comprised dense MgO grains surrounded by thin layers of forsterite (Mg2SiO4).