What Are Alumina Carbon Refractory Bricks and Their Functions?

1. Introduction to Alumina Carbon Refractory Bricks

Alumina carbon refractory bricks (Al₂O₃-C bricks) are advanced composite materials made primarily from alumina (Al₂O₃) and carbon (C), often supplemented with additives like silicon carbide (SiC) or metallic silicon. These bricks are classified into two types: fired Al₂O₃-C bricks (ceramic-bonded) and unfired Al₂O₃-SiC-C bricks (carbon-bonded). They are widely used in high-temperature industrial applications due to their exceptional thermal stability and resistance to chemical erosion.

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2. Key Components and Raw Materials

The primary raw materials include high-grade bauxite, fused corundum, or white alumina as Al₂O₃ sources, and flake graphite for carbon content. Additives like SiC (4–10%) enhance oxidation resistance, while phenolic resin (4–6%) serves as a binder. Some formulations incorporate zirconia (ZrO₂) to improve thermal shock resistance and strength.

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3. Manufacturing Process

Fired Al₂O₃-C bricks undergo high-temperature treatment in reducing atmospheres, forming a ceramic-carbon composite structure. Unfired Al₂O₃-SiC-C bricks skip this step, relying on carbon bonding for integrity. The process involves mixing, pressing, and curing, similar to magnesia-carbon bricks. Optimal particle size distribution (e.g., 40–60% coarse aggregate) ensures density and performance.

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4. Superior Performance Characteristics

These bricks excel in:

• Thermal shock resistance: Low thermal expansion from graphite minimizes cracking.

• Slag resistance: Carbon’s non-wettability shields against acidic/neutral slags.

• Mechanical strength: Fired bricks achieve 110–120 MPa compressive strength.

• Oxidation resistance: SiC and metal additives inhibit carbon oxidation.

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5. Industrial Applications

Fired Al₂O₃-C bricks are ideal for continuous casting (e.g., slide gates, submerged nozzles). Unfired bricks dominate iron pretreatment (e.g., torpedo ladle linings, blast furnaces) due to alkali/Na₂O slag resistance. They also replace traditional bricks in blast furnaces, cutting costs by 2/3.

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6. Advantages Over Traditional Refractories

Compared to high-alumina or magnesia-carbon bricks, Al₂O₃-C bricks offer:

• Longer lifespan in corrosive environments (e.g., iron/steel ladles).

• Better thermal conductivity and lower creep rates.

• Cost efficiency with comparable performance to Si₃N₄-bonded SiC bricks.

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7. Limitations and Mitigation Strategies

Weaknesses include vulnerability to:

• Alkaline slags (Na₂O/CaO): Add ZrO₂ or increase Al₂O₃ content to counteract.

• Reductive gases (CO/H₂): Al₄SiC₄ phases enhance stability.
  Regular maintenance and antioxidant coatings further extend service life.

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8. Future Trends and Innovations

Emerging variants like Al-Zr-C bricks leverage ZrO₂’s phase transformation for higher strength (2700°C melting point). Research focuses on nano-additives and hybrid composites (e.g., Al₂O₃-MgO-C) for extreme conditions. Their role in sustainable steelmaking and energy-efficient furnaces is expanding globally.

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