Colloidal silica as an anti-hydroxylation binder for pressed MgO structures

MgO-bricks for steelmaking require thermoset resin-based binders and pre-sintering steps above 1400ºC before installation to ensure strength and dimensional stability. Replacing resins with aqueous-based binders and employing shorter sintering schedules would save energy. An authors' study combined MgO particles and aqueous dispersion of silanized colloidal silica in a self-flowing suspension, reducing hydroxylation damages and improving strength before and after sintering. This study evaluated the same combination of raw materials in a pressed system. Fine MgO was sprayed with colloidal silica (0–0.04 SiO₂-MgO molar ratio) and shaped by conventional uniaxial pressing. A thin magnesium silicate hydrate (4MgO.5SiO₂·H₂O) coating formed at the surfaces of MgO particles and prevented hydroxylation damage. During sintering, it softened and became a mixture of amorphous silica and Forsterite (Mg₂SiO₄). Compared to the silica-free reference, samples containing colloidal silica showed a two-to-three-fold green strength increase and higher densification levels after sintering at lower temperatures.