Introduction:
Tabular alumina has been widely used in high performance refractories for steel, foundry, petrochemical and ceramics for 40 years. Tabular alumina is the dominant synthetic high-purity alumina aggregate due to its high refractoriness, excellent thermal shock resistance, creep resistance and wear resistance. Although the overall consumption of refractory materials has fallen sharply, especially in the application of steel manufacturing, the use of tabular alumina has not only increased relatively, but increased absolutely. The steady increase in the proportion of monolithic refractories introduced in continuous casting and the violent trend of high-quality steel are the driving forces for the development of tabular alumina-based refractories.
Performance:
Tabular corundum is a dense, fully shrunk, sintered α-Al2O3 aggregate structure composed of 50-400 μm grains. Tabular corundum gets its name from the shape of its grains like slabs. Tabular alumina was prepared by rapidly calcining ultrafine α-Al2O3 pellets at a temperature slightly lower than the melting temperature. After heat treatment, crush or grind 18-20mm pellets to obtain tabular corundum of various sizes.
The low content of silicon oxide, iron oxide and titanium oxide in corundum is very important for excellent high temperature performance. Ultra-low levels of dissolved iron oxides, typically less than 0.002%, are very important for phosphate-bonded refractories. Comparing sintered tabular alumina with other synthetic high-alumina aggregates, such as fused white corundum, the biggest difference is found to have a finer-sized impurity content. This can cause huge performance differences, especially high temperature performance. The introduction of higher impurity content in finer size greatly reduces the high temperature bulk stability and creep resistance. Comparing the porosity of fused white corundum and tabular corundum, a huge difference can be seen. Although the total porosity of the two aggregates is the same, the grain porosity is significantly different.
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The open porosity of fused grains is 2-3 times that of sintered grains. Most of the pores of fused alumina are composed of large open pores, while more than half of the pores of tabular corundum are closed pores. A high proportion of closed pores is necessary for high thermal shock resistance, which is typical of tabular alumina.
Tabular alumina exhibits high thermal shock resistance and high strength. Scanning electron microscope photos show that the surface of tabular corundum grains is not as smooth as that of fused corundum grains, but rather rough with shallow hemispherical pores. This surface structure promotes its reaction and mechanical interlocking with the matrix to increase the strength of the refractory.
The main properties of tabular corundum are as follows:
1. High-purity Al2O3 concentration of 99.4%;
2. Very high crystal hardness;
3. Low open porosity and 2-3 times higher closed porosity;
4. High particle packing density 3.55-3.6g/cm3;
5, high melting point: 2000 ℃ ;
6, chemical inertness;
7, good thermal shock resistance;
8, excellent volume stability;
9, the existence of microcracks;
10, high single grain strength.
The main application fields of tabular alumina:
The properties of tabular alumina have many applications in the field of refractories. The main field of application of tabular alumina, tabular alumina is suitable for ceramic, chemical and water-bound matrices. Tabular alumina can be used alone and in combination systems or with calcined and/or activated alumina. Because tabular corundum exhibits extremely high purity even as a fine powder, it can be used to improve the properties of lower alumina aggregates. For example, bauxite and fused brown corundum, coarse particles of these aggregates and medium and fine powders of tabular corundum are used. It has already been mentioned that the increase in the consumption of tabular alumina mainly comes from the continuous casting of steel. Especially for skids, dip tubes and nozzles, the use of tabular alumina is an industry standard requirement.
