Challenge: How does the uniqueness of tabular alumina improve my refractory performance?
Solution: The dense structure of Tabular Alumina allows less slag and metal infiltration of your refractory. For more than 50 years Tabular Alumina has been widely used in high performance refractories for many applications in steel, foundries, petrochemicals, and ceramics. Its superior refractoriness, thermal shock-, creep-, and abrasion resistance has made Tabular Alumina the dominant synthetic high purity Al2O3 aggregate. Tabular Alumina is a dense, sintered α-Al2O3 with large 50-400 µm crystals forming an aggregate structure. The tablet like shape gives Tabular its name. The material is produced by rapid heating of granulated balls of super fine α-Al2O3 up to temperatures shortly below fusing. After heat treatment, about 20 mm sized balls are crushed and ground into a variety of different sizes. Due to the sintering process, Tabular Alumina (T60/T64) shows very homogeneous properties, such as low impurity level, high bulk specific gravity, and low open porosity (Figure 1). It is superior to other natural and synthetic material, like fused aluminas. Whereas Tabular Alumina production provides a very homogenous alumina aggregate, the cooling of a fused alumina block results in a quite inhomogeneous product. Rapid cooling at the outside results in small crystals, whereas slower cooling towards the center of the block results in larger crystals. Impurities with the lowest melting point (e.g. ß-alumina= Na2O*11Al2O3) are concentrated in the center of the block. Due to the lower hardness of ß-alumina (Mohs hardness = 6) than α-Al2O3 (Mohs hardness = 9), ß-alumina concentrates in fused alumina fines. White fused alumina fines can carry a significant amount of impurities, e.g. soluble soda, which has a tremendous negative impact on castable setting behavior and overall refractoriness. Also, due to foaming in the production process, white fused alumina can show very high porosity, which is obvious in the picture below [Figure 2]. Such pores can be easily infiltrated by molten slag or metal and would reduce the wear resistance of refractories.