Refractory materials encompass a wide range of types and applications, and thus, can be classified through various methods. The most widely adopted classification systems are based on chemical properties and chemical-mineral composition, as they effectively reflect the material structure, composition, et performances. Below is a comprehensive classification of refractory materials.

1. Classification by Chemical Properties

Refractory materials are typically divided into three categories based on their chemical properties:

  • Acidic Refractories
    Mainly composed of silicon dioxide (SiO₂). Typical products include silica bricks and zircon bricks, which are resistant to acidic slags.

  • Basic Refractories
    Primarily composed of magnesium oxide (MgO) and calcium oxide (CaO). This group includes magnesia bricks, magnesia-alumina bricks, magnesia-chrome bricks, and dolomite bricks, suitable for resisting basic slags.

  • Neutral Refractories
    Based on alumina (Al₂O₃), chromia (Cr₂O₃), and carbon, these include corundum bricks, high alumina bricks, and carbon bricks, offering resistance to both acidic and basic slags.

2. Classification by Chemical-Mineral Composition

This is the most widely used classification method in the industry. It includes:

  • Silica Refractories:
    Silica bricks, fused quartz products.

  • Silica-Alumina Refractories:
    Clay bricks, semi-silica bricks, high alumina bricks, mullite bricks, corundum bricks.

  • Magnesia-Based Refractories:
    Magnesia bricks, magnesia-alumina bricks, magnesia-chrome bricks, dolomite bricks.

  • Carbon-Based Refractories:
    Carbon bricks, graphite-clay products.

  • Zirconia-Based Refractories:
    Zircon bricks, zircon-mullite bricks, zirconia-corundum bricks (AZS).

  • Special Refractories:
    High-purity materials with melting points above 2000°C, such as pure oxides, carbides, nitrides, borides, and metal ceramics.

3. Classification by Refractoriness

  • Common Refractories: 1580–1770°C

  • Advanced Refractories: 1770–2000°C

  • Super Refractories: >2000°C

4. Classification by Forming Process

  • Natural rock materials

  • Slurry casting refractories

  • Plastic forming refractories

  • Semi-dry pressed refractories

  • Ramming refractories (mechanical or manual)

  • Fused cast products

5. Classification by Firing Method

  • Unfired Bricks

  • Fired Bricks

  • Monolithic Refractories (Unshaped Materials)

6. Classification by Apparent Porosity

  • <3%: Ultra-dense products

  • 3–10%: High-density products

  • 10–16%: Dense products

  • 16–20%: Sintered products

  • 20–30%: Ordinary products

  • 45–85%: Lightweight products

  • 85%: Ultra-lightweight products

7. Classification by Chemical-Mineral Composition: Product Examples

Silica-Alumina Refractory Series

  • Silica Bricks (SiO₂ > 93%): for coke ovens, hot blast stoves, glass kilns

  • Semi-silica Bricks

  • Fireclay Bricks (Al₂O₃ 30–48%): for blast furnaces, hot blast stoves

  • High Alumina Bricks (Al₂O₃ 48–90%): including sillimanite, mullite, and corundum bricks

  • Mullite Bricks

  • Corundum Bricks: sintered, fused, chrome-corundum, corundum-mullite

Basic Refractory Series

  • Magnesia Bricks: fired, chemically bonded, asphalt bonded

  • Magnesia-Alumina Bricks

  • Magnesia-Chrome Bricks: direct bonded, fused cast

  • Dolomite Bricks

  • Magnesia-Dolomite Bricks

  • Magnesia-Silica Bricks

Zirconia-Containing Refractories

  • Zircon Bricks

  • Fused Cast AZS Bricks

  • Zircon-Mullite Bricks

Carbon-Containing Refractories

  • Alumina-Carbon Bricks: for ladles, sliding gates

  • Magnesia-Carbon Bricks: for converters, electric arc furnaces

  • Zirconia-Carbon Bricks

  • Dolomite-Carbon Bricks

  • Graphite-Clay Refractories

  • Silicon Carbide Bricks: clay-bonded, nitride-bonded, recrystallized

  • Carbon Bricks: for blast furnaces, electrolytic cells

Monolithic Refractories (Unshaped Materials)

  • Refractory Aggregates: dense and lightweight

  • Refractory Powder

  • Refractory Castables: dense, lightweight

  • Refractory Cement and Mortar

  • Ramming Mixes, Plastic Refractories, Spraying Mixes

  • Conclusion

    Understanding the classification of refractory materials provides a systematic approach to selecting the right material for each industrial application. Among the numerous classification systems, chemical-mineral composition is the most comprehensive and widely adopted, as it directly reflects the refractory’s structure, performance, and suitability for high-temperature environments.

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