Why Tabular, Calcined and Reactive Alumina for Refractories?

When formulating high-performance unshaped refractories, tabular alumina, calcined alumina and reactive alumina are the three most frequently used alumina-based materials. They act respectively as skeletons, fillers and sintering aids, jointly governing the thermal shock resistance, densification and corrosion resistance of castables or ramming mixes. A small addition of mullite can further refine the high-temperature mechanical behaviour.

Tabular alumina is produced by rapidly sintering high-purity alumina above 1900°C. It develops plate-like crystals with abundant closed micropores and extremely low apparent porosity. This structure delivers high refractoriness, outstanding thermal shock resistance and creep resistance. In areas exposed to severe temperature fluctuations, such as ladle impact zones and cement rotary kiln outlets, tabular alumina aggregates resist spalling effectively while maintaining the lining's volume stability.

High temperature calcined alumina micro powder has completed complete alpha phase transformation, with complete crystal development and low chemical activity. It is mainly used to fill the gaps between coarse particles and improve the packing density. Activated alumina micro powder is controlled by low-temperature calcination to retain a high specific surface area and reactivity. At high temperatures, it preferentially forms a sintering neck, promotes matrix densification, reduces the sintering temperature of the material, significantly improves the strength at room temperature and medium temperature, and enhances the ability to resist slag penetration.

In a typical formula, plate-like corundum forms an aggregate network, calcined alumina micro powder fills the intermediate gaps, and activated alumina micro powder provides sintering activity, forming a tight particle size distribution among the three. When a small amount of mullite is introduced, its needle shaped crystals are generated in situ at high temperatures, which can further improve the thermal shock resistance and high-temperature flexural strength, and reduce structural peeling caused by temperature difference stress. Thoroughly understanding the characteristic differences of these raw materials has direct engineering significance for extending the life of kiln lining and reducing the consumption of refractory materials per ton of steel.

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