Characteristics of Tabular Alumina (Tabular Corundum) and Its Application in Refractories for the Steel Industry

Tabular alumina is also known as tabular corundum in China. It is a pure sintered alumina that shrinks without any additives such as MgO and B2O3. It has a coarse crystal and well-developed α-Al2O3 crystal structure. Since it is sintered at a temperature slightly lower than 2035℃, close to the melting point of Al2O3, the Al2O3 has been transformed into corundum α-Al2O3. It is called "tabular alumina" because this material is composed of hexagonal tabular α-Al2O3 crystals with a median diameter of 40 to 200μm. During rapid sintering, the coarse crystals formed by submicron-sized α-Al2O3 crystals contain closed spherical pores, which make tabular alumina have excellent heating volume stability and good thermal shock resistance.

The application of tabular alumina as a large-scale refractory aggregate began in the mid-1950s, when new refractory binders were developed, such as high-purity calcium aluminate cement and phosphate binders. The application of these binders greatly improves the erosion resistance and wear resistance oftabular alumina refractory materials.

1. Characteristics of Tabular alumina

Ordinary sintered alumina is generally fired in a rotary kiln or tunnel transport. Due to temperature restrictions, a small amount of sintering promoters such as MgO and CaO are usually added to promote its density. Therefore, the porosity of ordinary sintered alumina is low, and the crystals are fine and dense, resulting in poor thermal shock resistance.

Tabular alumina is a recrystallized α-Al2O3 that is rapidly sintered and sintered at a high temperature above 1900℃. It does not contain any additives and has the following microstructure characteristics:

① It is composed of well-developed α-Al2O3 crystals;

② The α-Al2O3 crystals are coarse, with a median diameter of 40~200μm, and its two-dimensional crystal morphology is flat and interlaced with each other;

③ The α-Al2O3 crystals contain many 5~15μm circular closed pores; and the open pores are less, generally 2%~3%;

④ Due to the presence of (about 0.16%), there is β-Al2O3 in the structure, but all of them grow at the grain boundaries of the α-Al2O3 crystals.

 Due to the above structural characteristics of plate-shaped alumina, it has the following physical properties:

① High melting point, about 2040℃;

② Large grain hardness, Mohs hardness 9, Knoop hardness 2000;

③ Chemical corrosion resistance, except for hydrofluoric acid and phosphoric acid, most alkalis and mineral acids have no effect on plate-shaped alumina;

④ Due to the absence of microcracks and large internal pores, its strength is relatively high; at the same time, its strength does not decrease much when subjected to thermal shock, so the thermal shock stability is better (see Table 1);

⑤ high thermal conductivity and high resistivity, with good electrical properties at high frequency and high temperature.

The typical properties of Tabular alumina are listed in Table 1.tabular alumina is mostly used as refractory aggregate, and is also used as an additive to enter the matrix. When combined with other refractory raw materials, it has the following advantages: high refractoriness; high heat load strength; small creep; high density; low permeability; good thermal shock stability and wear resistance; low thermal shrinkage; high purity, reducing the impact of impurities on the high-temperature performance of the material.

2. Application of tabular alumina in refractory materials for steel industry

Due to a series of properties of tabular alumina, it becomes an ideal refractory raw material. It can be used as aggregate in refractory materials such as Al2O3-C, Al2O3-SiO2-C and Al2O3-Cr2O3, and can also be added to other high-alumina amorphous refractory materials.tabular alumina amorphous refractory materials bonded with phosphate and calcium aluminate cement are widely used. All parts where fused corundum or white corundum is used can be replaced by tabular alumina to improve the performance of refractory materials.

The application oftabular alumina in the steel industry includes almost all parts where alumina refractory materials are used, from blast furnaces, hot blast furnaces, mixing iron furnaces, fish tanks to converters, secondary refining furnaces, mold casting and continuous casting ladle, tundish, soaking furnaces and heating furnaces (Table 2).

In the ceramic industry, tabular alumina is used in kiln furniture to significantly improve its performance. For example, it can be used in ceramic rollers to improve their thermal shock stability and deformation resistance; it can be used in the manufacture of saggers and shelves for firing spark plugs, alumina balls and other high-temperature ceramics, and its life span is significantly improved. tabular alumina can also be used as insulators, as well as catalyst carriers for high-temperature reactions that require low porosity, high strength and high purity.