描述
Specification of tabular alumina:
Tabular alumina is also known as tabular corundum in China. It is a pure sintered alumina that shrinks without any additives such as MgO and B2O3. It has a coarse crystal and well-developed α-Al2O3 crystal structure. Since it is sintered at a temperature slightly lower than 2035℃, close to the melting point of Al2O3, the Al2O3 has been transformed into corundum α-Al2O3. It is called “tabular alumina” because this material is composed of hexagonal tabular α-Al2O3 crystals with a median diameter of 40 to 200μm. During rapid sintering, the coarse crystals formed by submicron-sized α-Al2O3 crystals contain closed spherical pores, which make tabular alumina have excellent heating volume stability and good thermal shock resistance.
The application of tabular alumina as a large-scale refractory aggregate began in the mid-1950s, when new refractory binders were developed, such as high-purity calcium aluminate cement and phosphate binders. The application of these binders greatly improves the erosion resistance and wear resistance oftabular alumina refractory materials.
1-3mm Grain size index of tabular corundum：
| Size | 1-3mm | ||
| Particle size range | 1-3mm | 2-3mm | 1-2mm |
| Typical value（%） | 99 | 52 | 47 |
| Value（%） | 90 | 30 | 30 |
1-3mm Physical and chemical indexes of tabular corundum：
| Particle | Al2O3
（％） |
Fe2O3
（％） |
Na2O
（％） |
SiO2
（％） |
Density
g/cm3 |
Apparent porosity
（％） |
Water absorption（％） | |
| 1-3mm | Standard | ≥99.2 | ≤0.2 | ≤0.4 | ≤0.2 | ≥3.5 | ≤5.0 | ≤1.5 |
| Test | 99.26 | 0.06 | 0.3 | 0.08 | 3.56 | 3.8 | 1.2 | |
Tabular alumina is a recrystallized α-Al2O3 that is rapidly sintered and sintered 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 with each other;
- The α-Al2O3 crystals contain many 5~15μm circular closed pores; and 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 plate-shaped alumina, it has the following physical properties:
- High melting point, about 2040℃;
- Large grain hardness, Mohs hardness 9, Knoop hardness 2000;
- Chemical corrosion resistance, except for hydrofluoric acid and phosphoric acid, most alkalis and mineral acids have no effect on plate-shaped alumina;
- Due to the absence of microcracks and large internal pores, its strength is relatively high; at the same time, its strength does not decrease much when subjected to thermal shock, so the thermal shock stability is better (see Table 1);
- High thermal conductivity and high resistivity, with good electrical properties at high frequency and high temperature.
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