Hydration-resistant lime refractories from Egyptian limestone and ilmenite raw materials

Four refractory lime batches were processed from the pure limestone economically available at Beni Khaled, El Menia, Egypt up to firing at 1550°C using a two-stage firing process. The ferri-ilmenite ore existing at Abu Ghalaga, Eastern Desert was added as a dopant material in amounts of 0.5, 1.0, 2.0, 3.0%. Densification parameters and hydration resistance of the fired grains were investigated. The most dense hydration resistant grains were selected to assess their refractory quality by determining load-bearing capacity and thermal shock resistance. These results were interpreted in the light of phase composition and microstructure of the fired grains. It is concluded that dense and hydration resistant lime grains can be processed by doping the pure limestone powder with 2.0–3.0 wt.% of ferri-ilmenite before firing up to 1550°C. Such level of ilmenite content has contributed in the densification of lime particles in the solid state and also by limited amount of the developed liquid phase. Hence, direct-bonded lime network is formed with partial interruption by a platey calcium–alumino–ferrite–titanate phase, which crystallized on cooling from the liquid phase at the grain boundaries of the lime–lime network. This improves the bulk density of fired grains to about 3.2–3.3 g/cm3 and its rate of hydration to 4.15–3.80 g/h without significant deterioration of its load-bearing capacity and thermal shock resistance.