Role of Mg(OH)2 in pore evolution and properties of lightweight brine magnesia aggregates

Abstract

Lightweight magnesia aggregates were fabricated using high-purity MgO agglomerates with the addition of Mg(OH)2 as a pore former. The pore evolution and its relationship to the resulting properties were investigated. Mg(OH)2 decomposition increased the number of inter-agglomerate pores, which subsequently affected the porosity and pore structure. When Mg(OH)2 was 0–20 wt%, the inter-agglomerate pores were converted to both open and closed small pores, which effectively reduced the thermal conductivity and improved the thermal shock resistance (TSR) by accommodating thermal stress and inducing crack deflection. Small pores also favored the formation of a dense (Mg, Fe)O corrosion layer, preventing further slag penetration. However, large open pores occurred with further increasing Mg(OH)2 content, which dramatically deteriorated the TSR and slag resistance. The specimen with 20 wt% Mg(OH)2 exhibited the best overall performance, with a thermal conductivity of 16.6 W/(m·K) at 500 °C, and a residual flexural strength ratio of 32.3%; its slag resistance was comparable with that of dense magnesia.