Main Types of Corundum Bricks

Corundum bricks are high-grade refractory bricks primarily composed of corundum, which is crystalline aluminum oxide (Al₂O₃). Corundum can be naturally occurring or synthetically produced through processes such as electric arc melting or sintering. Compared with conventional high-alumina bricks, corundum bricks offer:

• Higher refractoriness under load

• Superior mechanical strength at elevated temperatures

• Excellent resistance to slag erosion

• Strong chemical stability in oxidizing and reducing atmospheres

• Low porosity and high density (depending on type)

Because of these properties, corundum bricks are typically used in extremely demanding thermal environments where ordinary refractory materials would fail.

1. Sintered Corundum Bricks

Production Process

Sintered corundum bricks are manufactured by mixing high-purity alumina raw materials (such as calcined alumina or fused corundum), adding binders, shaping through pressing, and firing at high temperatures (usually above 1700°C).

During sintering, particles bond together without melting completely, forming a dense and strong microstructure.

Key Characteristics

• Alumina content: generally 90%–99%

• High refractoriness

• Good thermal shock resistance

• Excellent compressive strength

• Moderate porosity compared to fused types

Applications

Sintered corundum bricks are widely used in:

• Blast furnace hearths

• Ladles and tundishes

• Cement rotary kilns

• Glass furnace superstructures

They offer a good balance between performance and cost, making them one of the most commonly used types of corundum bricks in industrial applications.

2. Fused Cast Corundum Bricks

Production Process

Fused cast corundum bricks are produced by melting high-purity alumina in an electric arc furnace at extremely high temperatures. The molten material is then cast into molds and slowly cooled to form a dense crystalline structure.

This casting process results in very low porosity and a highly compact microstructure.

Key Characteristics

• Extremely high density

• Very low apparent porosity

• Superior resistance to slag and glass corrosion

• Outstanding wear resistance

• Excellent performance under high mechanical stress

Applications

Fused cast corundum bricks are often selected for:

• Glass melting furnaces

• Petrochemical reactors

• Non-ferrous metal smelting furnaces

• Waste incineration systems

Because of their outstanding corrosion resistance, they are particularly suitable for contact with molten glass or aggressive slags.

3. Mullite-Bonded Corundum Bricks

Mullite-bonded corundum bricks combine corundum aggregates with mullite as the bonding phase. Mullite (3Al₂O₃·2SiO₂) improves thermal shock resistance while maintaining high refractoriness.

Characteristics

• High thermal shock resistance

• Good structural stability

• Moderate thermal expansion

• Strong resistance to mechanical spalling

Advantages

The mullite bonding phase enhances flexibility in the structure, making these bricks less prone to cracking under rapid temperature changes.

Applications

They are commonly used in:

• Ceramic kilns

• Tunnel kilns

• Rotary kilns

• Heat treatment furnaces

Mullite-bonded corundum bricks are ideal where temperature fluctuations are frequent.

4. Chrome Corundum Bricks

Chrome corundum bricks are produced by combining corundum with chromium oxide (Cr₂O₃). The addition of chromium significantly enhances resistance to chemical corrosion and slag penetration.

Characteristics

• High refractoriness

• Exceptional slag resistance

• Excellent high-temperature strength

• Strong resistance to acidic and basic slags

Applications

These bricks are widely used in:

• Glass furnaces (particularly in contact with molten glass)

• Copper and nickel smelting furnaces

• Waste incinerators

• Chemical reactors

However, environmental regulations in some regions may limit the use of chromium-containing refractories due to potential environmental concerns.

5. Zirconia Corundum Bricks (AZS Bricks)

Zirconia corundum bricks, often known as AZS bricks (Alumina-Zirconia-Silica), contain zirconium oxide (ZrO₂) in addition to alumina.

Characteristics

• Extremely strong resistance to glass corrosion

• High density

• Excellent thermal stability

• Good resistance to erosion

Applications

AZS bricks are extensively used in:

• Glass melting tanks

• Float glass production lines

• Fiberglass furnaces

Their resistance to molten glass makes them one of the most important refractory materials in the glass industry.

6. Phosphate-Bonded Corundum Bricks

Phosphate-bonded corundum bricks use phosphoric acid or aluminum phosphate as a binder instead of high-temperature ceramic bonding.

Characteristics

• High early strength

• Good abrasion resistance

• Lower firing temperature required

• Excellent mechanical performance

Applications

These bricks are often applied in:

• Cement kilns

• Rotary kilns

• Areas subject to high mechanical wear

Because they can achieve strong bonding at relatively lower temperatures, they are suitable for applications requiring quick installation and fast commissioning.

7. Lightweight Corundum Insulating Bricks

Unlike dense corundum bricks, lightweight corundum insulating bricks are designed to provide both refractoriness and thermal insulation.

Characteristics

• Lower bulk density

• Higher porosity

• Reduced thermal conductivity

• Adequate high-temperature strength

Applications

They are used in:

• Backup linings

• Furnace insulation layers

• Energy-saving kiln designs

Although they do not match the mechanical strength of dense corundum bricks, their insulation properties help reduce heat loss and improve energy efficiency.