What is the thermal expansion coefficient of high alumina castables at different temperatures?

The thermal expansion coefficient of high alumina castables exhibits periodic characteristics with temperature changes, and the specific values and variation patterns are as follows:

1、 Normal to medium temperature range (20~600 ℃)

Initial stage (20~200 ℃)

The coefficient of thermal expansion rapidly increases, especially for castables containing calcium aluminate cement (such as CAH10), which experience volume expansion due to cement dehydration reaction, with a coefficient of up to 7.0~8.0 × 10 ⁻⁶/℃.

The expansion coefficient of pure high alumina castable (without cement) is relatively low, about 5.0~6.0 × 10 ⁻⁶/℃.

Medium temperature stage (200~600 ℃)

The transformation of cement crystal structure (such as CAH10 → C3AH6) is accompanied by shrinkage, offsetting some expansion, and the thermal expansion coefficient drops to 5.5~6.5 × 10 ⁻⁶/℃.

2、 High temperature range (600~1200 ℃)

600~1000℃

The formation of calcium aluminate phase and sintering shrinkage are dominant, and the thermal expansion coefficient slowly increases to 6.0~7.0 × 10 ⁻⁶/℃.

The low cement formula (CaO<1%) has a lower expansion coefficient (about 5.0~6.0 × 10 ⁻⁶/℃) due to the reduction of the formation of low melting phases.

1000~1200℃

The densification of the material accelerates, and the expansion coefficient further increases to 7.0~8.0 × 10 ⁻⁶/℃, but high-purity corundum aggregate can suppress the growth (maintaining 6.5 × 10 ⁻⁶/℃).

3、 Ultra high temperature range (1200~1500 ℃)

1200~1400℃

The appearance of liquid phase leads to a reduction in particle spacing and a decrease in expansion coefficient to 5.0~6.0 × 10 ⁻⁶/℃.

1400~1500℃

The Mo Lai petrochemical reaction is completed, the structure is stable, and the expansion coefficient is maintained at 4.5~5.5 × 10 ⁻⁶/℃.

4、 Key influencing factors

Compositional differences

The expansion coefficient of corundum quality (Al ₂ O ∝ ≥ 90%) is lower than that of high alumina bauxite base (Al ₂ O ∝ 55-80%).

The addition of silicon carbide (SiC) can reduce the coefficient of expansion to 4.5 × 10 ⁻⁶/℃ (1000 ℃).

Type of binder

Phosphate binders are more stable than calcium aluminate cement and have less fluctuation in high-temperature expansion coefficient.

Temperature range (℃) coefficient of thermal expansion (× 10 ⁻⁶/℃) Material type: 20~2007.0~8.0 Cement bonded high alumina material 200~6005.5~6.5 Low cement high alumina material 600~10006.0~7.0 Corundum silicon carbide composite 1000~12007.0~8.0 Ordinary high alumina material 1200~15004.5~5.5 Ultra low cement corundum material

summary

The thermal expansion coefficient of high alumina castables is affected by temperature, composition, and bonding system, and the formula should be selected according to the working conditions during design. Low cement/non cement technology can significantly improve high-temperature stability.