Tabular alumina is a dense, fully shrunk, sintered α-Al2O3 aggregate structure consisting of 50-400μm grains. Tabular corundum is named for its plate-like grain shape. Tabular alumina is prepared by rapid calcination of ultrafine α-Al2O3 pellets at slightly below the melting temperature. After heat treatment, the 18-20mm pellets are crushed or ground to obtain tabular corundum of various sizes.
For excellent high temperature properties, low levels of silicon oxide, iron oxide and titanium oxide in the corundum are very important. The ultra-low content of soluble iron is typically less than 0.002% for phosphate bonded refractories. When comparing sintered tabular alumina with other synthetic high alumina aggregates, such as fused white corundum, the biggest difference is the impurity content with finer size. This can cause huge performance differences, especially high temperature performance. Higher impurity content introduced in finer size greatly reduces high temperature volume stability and creep resistance. A huge difference can be seen when comparing the porosity of fused white corundum and tabular corundum. Although the total porosity of the two aggregates is the same, there is a significant difference in the grain pores.
The open porosity of the fused grains is 2-3 times that of the sintered grains. Most of the pores of fused alumina are composed of large open pores, while more than half of the pores of tabular alumina are closed pores. A high proportion of closed pores is necessary for high thermal shock resistance, which is a typical feature of tabular corundum.
Tabular alumina exhibits high thermal shock resistance and high strength. Scanning electron micrographs show that the surface of tabular corundum grains is not as smooth as that of fused alumina grains, but is rougher with shallow hemispherical pores. This surface structure promotes its reaction and mechanical interlocking with the matrix, thereby improving the strength of the refractory.
The main properties of tabular alumina are as follows:
1. High-purity Al2O3 concentration of 99.4%;
2. Extremely high hardness of the crystal;
3. Low open porosity and 2-3 times higher closed porosity;
4. High particle packing density of 3.55-3.6g/cm3;
5. High melting point: 2000℃;
6. Chemical inertness;
7. Good thermal shock resistance;
8. Excellent volume stability;
9. The presence of microcracks;
10. High single grain strength.
