What are the main components of high alumina bricks?

High alumina brick is a refractory material mainly composed of alumina (Al ₂ O3), with an Al ₂ O3 content usually ≥ 48%, and is classified into different grades according to the content. The following are its main components and related information:

1. Main components

Aluminum oxide (Al ₂ O3): the core component of high alumina bricks, with a content usually above 48%, and some advanced products (such as corundum bricks) can reach over 90%.

Silicates and other impurities, including SiO ₂, Fe ₂ O3, TiO ₂, etc., can affect refractoriness and slag resistance.

2. Classification

High alumina bricks are divided into three categories based on their Al ₂ O ∝ content:

Grade I high alumina brick: Al ₂ O ∝ ≥ 75%, with a fire resistance of up to 1800 ℃, suitable for high-temperature furnace lining (such as electric furnace top).

Grade II high alumina brick: Al ₂ O ∝ 60%~75%, used for hot blast furnaces, rotary kilns, etc.

Grade III high alumina brick: Al ₂ O ∝ 48%~60%, suitable for medium temperature environments (such as glass melting furnaces).

3. Mineral composition

The microstructure of high alumina bricks is mainly composed of the following phases:

Mullite (3Al ₂ O ∝· 2SiO ₂): When the Al ₂ O ∝ content is low (such as grade II and III), it dominates and affects the thermal shock resistance.

Corundum (α - Al ₂ O3): When the content of Al ₂ O3 is high (such as grade I), it becomes the main crystalline phase, improving the refractoriness and high-temperature strength.

Glass phase: a low melting point phase formed by impurities that affects the load softening temperature.

4. Source of raw materials

High alumina alumina: The main raw material contains monohydrate alumina (α - Al ₂ O ∝· H ₂ O) and kaolinite.

Synthetic raw materials: such as fused alumina and mullite, used for high-purity products.

5. Performance characteristics

Fire resistance: 1750~1790 ℃, better than clay bricks.

Slag resistance: Near neutral, acid resistant slag is superior to alkaline slag.

Load softening temperature: 1400~1550 ℃, which increases with the increase of Al ₂ O3 content.

High alumina bricks are widely used in industrial equipment such as blast furnaces, electric furnaces, and cement rotary kilns due to their excellent high temperature resistance and corrosion resistance.