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The difference between sintered corundum and tabular alumina

1.Sintered alumina

Sintered alumina is also called sintered corundum. It is a refractory clinker made of calcined alumina or industrial alumina powder as raw material, finely ground into balls or green bodies, and sintered at a high temperature of 1750-1900°C. Sintered alumina with a W(Al2O3) over 99% is mostly made of uniform fine-grained corundum directly combined, the apparent porosity is below 3.0%, the bulk density reaches 3.60g/cm3, and the refractoriness is close to the melting point of corundum. It has good volume stability and chemical stability, is not easily corroded by reducing atmosphere, molten glass and molten metal, and has good mechanical strength and wear resistance at room temperature and high temperature.

The bulk density and crystal size of sintered alumina are closely related to factors such as the type of raw materials used in the sintering process, the method of pelletizing or forming, the initial density of the body, the type and quantity of additives, and the calcination temperature. Adding less than 1% (mass fraction) of TiO2 can reduce the sintering temperature and increase the density of sintered alumina; adding more than 2% to 3% (mass fraction) of TiO2 will reduce its density; another effect of adding TiO2 is to make Obtain large-particle clinker, large-particle crystallized sintered alumina has good resistance to slag erosion. It is also possible to add 1% to 2% (mass fraction) of H3BO3 to promote the growth of corundum grains. Another purpose of adding H3BO3 is to react with the Na2O in the raw material to generate Na3BO3 and volatilize, reducing the Na2O content in the raw material. Sometimes in order to inhibit the abnormal growth of corundum crystals, a small amount of MgO can be added.

The calcination of sintered alumina is mostly carried out in an inverted flame kiln or a rotary kiln.

Sintered alumina is mainly used as a raw material for the production of sintered corundum bricks and amorphous refractories, and its usable temperature is quite high.

However, this kind of raw material causes crystal growth when the secondary heating time is long, and as a result, the solid solution limit may be lowered, and precipitates are generated at the grain boundary, which affects its high temperature performance.

2. Tabular alumina

Tabular alumina, also known as tabular corundum in China, is a pure, sintered alumina that has been fired without any additives and is completely shrunk.

Plate-shaped alumina is made of alumina powder. After being ground, shaped and dried, it is sintered in an ultra-high temperature kiln at a temperature slightly lower than the melting point of corundum, under the conditions of rapid heating and cooling, forming many tight bonds. The slab-columnar crystals are large, with a median diameter of 40-200 microns. The two-dimensional morphology of the crystals is flat and interspersed with each other. The crystal contains many circular closed pores of 5-15 microns, with fewer open pores. , Generally 2% to 3%.

Because the slab alumina does not add any additives, it has high purity, high melting point, high crystal grain hardness, high thermal load strength, low thermal shrinkage, high density, low air permeability, and good wear resistance, especially because there are many crystal grains. The small pores are closed, and the thermal shock stability is good. Except for hydrofluoric acid and phosphoric acid, most alkalis and inorganic acids have no effect on tabular corundum and are resistant to chemical attack.

Due to a series of characteristics of plate alumina, it becomes an ideal refractory raw material. It can be used as aggregate in refractory materials such as A12O3-C, A12O3-SiO2-C and Al2O3-Cr2O3, or it can be added to other refractories In high-alumina unshaped refractory materials. Plate-shaped alumina monolithic refractories combined with phosphate and calcium aluminate cement have been widely used. Any part where fused corundum or white corundum is used can be replaced with plate-shaped alumina, so that the performance of refractory materials can be improved.

The calcination of plate-shaped alumina is mostly carried out in a high-temperature shaft kiln.

The application of plate alumina in the iron and steel industry almost includes from blast furnaces, hot blast furnaces, mixing furnaces, torpedo tanks to converters, secondary refining furnaces, ladle, tundish, soaking furnaces and heating furnaces for die casting and continuous casting. Wait for all parts where alumina refractories are used.

In the ceramic industry, plate-shaped alumina is used in kiln furniture to significantly improve its performance. For example, it can improve the thermal shock stability and anti-deformation ability of ceramic rollers; it can be used to make saggers and slabs for high-temperature ceramics such as spark plugs, alumina balls, etc., and its service life has been significantly improved. Plate-shaped alumina can also be used as an insulator, and as a raw material for manufacturing catalyst carriers for high-temperature reactions requiring low porosity, high strength, and high purity.

Although sintered mullite and sintered spinel are also refractory clinker, they are synthetic raw materials.

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