From Macro to Nanomagnesia: Designing the in situ Spinel Expansion

Abstract

Magnesia grain size affects the in situ spinel formation kinetics and expansion of alumina–magnesia refractory castables. The use of coarse grains results in a large expansion and delays the reaction's starting temperature. In this work, the addition of an MgO source with different grain sizes (from macro, D max ≤0.1 mm, to nano, D 50 ≤20 nm) led to a broad linear expansion range (6%–2%), considering the spinel and the CA 6 formation. The addition of nanomagnesia, produced by a centrifugal‐type high‐energy ball milling, to high‐alumina refractory castables affected the spinel expansion and its starting temperature. The objective to estimate the reaction starting temperature was attained, reducing it from 1200° to 900°C. Nevertheless, the decrease of spinel expansion was not totally fulfilled, as a portion of the nanoparticles partly reagglomerated before mixing and behaved as coarser magnesia grains.