Properties and Applications of 2-5mm Tabular Alumina
Tabular alumina powder, also known as tabular corundum, is a pure sintered alumina that is completely sintered without any additives such as MgO and B2O3. It has a coarse crystal structure with well-developed α-Al2O3. During rapid sintering, the coarse crystals formed by the submicron α-Al2O3 crystals contain closed spherical pores, which makes the tabular alumina powder have excellent heating volume stability and good thermal shock resistance.
The application of tabular alumina powder as a large-scale refractory aggregate began in the mid-1950s, when new refractory binders such as high-purity calcium aluminate cement and phosphate binders were developed. The application of these binders greatly improves the corrosion resistance and wear resistance of tabular alumina refractory materials.
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 powder is a recrystallized α-Al2O3 that is sintered quickly and thoroughly at a high temperature above 1900℃. It does not contain any additives and has the following microstructure characteristics:
It is composed of well-developed α-Al2O3 crystals;
The α-Al2O3 crystals are coarse, with a median diameter of 40~200μm, and its two-dimensional crystal morphology is flat and interlaced;
The α-Al2O3 crystals contain many 5~15μm circular closed pores; while the open pores are less, generally 2%~3%;
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 tabular alumina, it has the following physical properties:
High melting point, about 2040℃;
High grain hardness, Mohs hardness 9, Knoop hardness 2000;
Chemical erosion resistance, except for hydrofluoric acid and phosphoric acid, most alkalis and mineral acids have no effect on tabular alumina;
Because it does not have microcracks and large internal pores, its strength is relatively high; at the same time, its strength does not drop much when subjected to thermal shock, so its thermal shock stability is good;
High thermal conductivity and high resistivity, with good electrical properties at high frequency and high temperature.
Tabular alumina powder is mostly used as refractory aggregate, and some are added into the matrix. It will have the following advantages when combined with other refractory raw materials: high refractoriness, high heat load strength, small creep, high density, low permeability, thermal shock stability, good wear resistance, low thermal shrinkage, high purity, and reduced influence of impurities on the high temperature performance of the material.
Due to a series of properties of tabular alumina powder, 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 of tabular alumina powder in the steel industry includes almost all parts where alumina refractory materials are used, from blast furnaces, hot blast furnaces, iron mixing furnaces, fish tanks to converters, secondary refining furnaces, mold casting and continuous casting ladle, tundish, soaking furnaces and heating furnaces.
In the ceramic industry, tabular alumina powder 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 slabs for firing high-temperature ceramics such as spark plugs and alumina balls, and its service life is significantly improved. Tabulae alumina powder can also be used as insulators, as well as catalyst carriers for high-temperature reactions that require low porosity, high strength and high purity.
