A táblázatos alumínium-oxid jellemzői és alkalmazásai

Tabular alumina, also called tabular corundum, is a pure sintered alumina that shrinks completely without adding any additives such as MgO, B2O3, stb. It has a coarse and well-developed α-Al2O3 crystal structure. Since it is sintered at a temperature slightly lower than 2035°C, close to the melting point of Al2O3, the Al2O3 has been transformed into corundum α-Al2O3. The reason why it is called “tabular-shaped alumina” is that this material is composed of hexagonal plate-shaped α-Al2O3 crystals with a median diameter of 40 to 200 μm. During rapid sintering, the coarse crystals formed by submicron α-Al2O3 crystals contain closed spherical pores, giving the tabular-shaped alumina excellent heating volume stability and good thermal shock resistance.

Characteristics of tabular alumina 

Ordinary sintered alumina is generally fired in a rotary kiln or tunnel. Due to temperature restrictions, a small amount of sintering accelerators such as MgO, CaO, stb. are usually added to promote its density. Ebből adódóan, ordinary sintered alumina has low porosity and fine and dense crystals, resulting in poor thermal shock resistance. Tabular alumina is recrystallized α-Al2O3 that is rapidly fired and completely sintered at a high temperature above 1900°C. It does not contain any additives. Its microstructure has the following characteristics:

1. Composed of well-developed α-Al2O3 crystals;
2. α-Al2O3 crystals are coarse, with a median diameter of 40 to 200 μm. The two-dimensional morphology of the crystals is flat and intertwined;
3. The α-Al2O3 crystal contains many 5~15μm circular closed pores; while the open pores are less, generally 2%~3%;
4. Due to the presence of α-Al2O3 (about 0.16%), β-Al2O3 exists in the structure, but It grows at the grain boundaries of α-Al2O3 crystals. Due to the above structural characteristics of the wrench-shaped alumina, it has the following physical properties: ① high melting point, about 2040°C; ② high grain hardness, Mohs hardness 9, Knoop hardness (Knoop) 2000; ③ chemical corrosion resistance, except Except for hydrofluoric acid and phosphoric acid, most alkalis and mineral acids have no effect on plate-shaped alumina;④ Since it does not have microcracks and large internal pores, its strength is high; at the same time, its strength does not drop much when subjected to thermal shock, so its thermal shock stability is good ;
5. High thermal conductivity and high resistivity, with good electrical properties at high frequency and high temperature.

Application of tabular alumina in refractory materials

Due to a series of strong properties of tabular corundum, 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-aluminum formálatlan tűzálló anyagok. Phosphate-bonded and calcium aluminate cement-bonded tabular corundum unshaped refractories are widely used. All areas where fused corundum or white corundum are used can be replaced with tabular alumina to improve the performance of refractory materials.

Applications in the steel industry

The applications of tabular alumina in the steel industry include almost everything from blast furnaces, forró kohók, mixing furnaces, fish pots to converters, secondary refining furnaces, mold casting and continuous casting ladles, tundishes and soaking furnaces and heating furnaces, and other parts that use alumina refractory materials.

Applications in the ceramic industry

In the ceramic industry, tabular alumina  is used in kiln furniture to significantly improve its performance. For example, when used in ceramic rollers, its thermal shock stability and deformation resistance can be improved; when used in the manufacture of saggers and shed plates for high-temperature ceramics such as fired spark plugs and alumina balls, the service life is significantly improved. Tabular alumina  can also be used as insulators and catalyst carriers for high-temperature reactions that require low pores, nagy szilárdságú, and high purity.