Refractory materials are materials capable of maintaining their structural integrity and performance stability in high-temperature environments; they are widely used in equipment such as high-temperature industrial furnaces, kilns, and furnace linings across industries including metallurgy, ceramics, glass, and cement. The following are the types of refractory materials and their primary applications:
I. Classification by composition
1. Acidic refractory materials
Quartz bricks: Made from quartz sand; characterized by high refractoriness and good acid resistance, but poor alkali resistance.
Aluminum silicate bricks: Contain bauxite; widely used and possess good thermal and chemical stability.
Clay bricks: Made primarily from fireclay (containing 30%–46% alumina); feature good thermal shock resistance and resistance to acidic slag corrosion.
Main composition: Primarily silicon dioxide (SiO₂).
Characteristics: Good acid resistance, but prone to reacting with basic slag.
Types:
Applications: Primarily used in thermal equipment such as coke ovens, glass melting furnaces, and acidic steelmaking furnaces.
2. Basic Refractories
Magnesia bricks: Composed primarily of magnesium oxide; they offer high-temperature resistance, alkali resistance, and excellent resistance to slag erosion.
Lime bricks: Made from quicklime (converting to calcium oxide); primarily used for blast furnace linings.
Magnesia-chrome bricks, chrome-magnesia bricks, magnesia-alumina bricks, dolomite bricks, forsterite bricks, etc.
Main constituents: Primarily magnesium oxide (MgO) or calcium oxide (CaO).
Characteristics: High refractoriness and strong resistance to basic slag.
Applications: Primarily used in basic steelmaking furnaces, non-ferrous metal smelting furnaces, cement kilns, etc.
3. Neutral Refractories
Chrome bricks: Materials containing chromium; they offer high-temperature and corrosion resistance and are primarily used in industries such as iron and steel smelting.
Mullite bricks: Composed mainly of mullite and produced by high-temperature sintering of clay minerals; they possess good thermal stability and strength, with a refractoriness generally ranging from 1200°C to 1400°C.
Zirconia-based refractories: Characterized by excellent high-temperature resistance and chemical stability; suitable for specialized applications in sectors such as papermaking and aerospace.
High-alumina refractories: Produced by firing bauxite; they feature high alumina content and high refractoriness, making them suitable for the high-temperature zones of high-temperature furnaces.
Characteristics: They do not readily react significantly with acidic or basic slags at high temperatures.
Applications: Widely used for the linings of various high-temperature furnaces, such as iron and steel smelting furnaces and ceramic kilns.
II. Classification by shape and manufacturing process
1. Refractory Bricks
Characteristics: The most common form of refractory material; possesses good strength and resistance to erosion/corrosion.
Applications: Widely used for lining equipment such as blast furnaces and industrial furnaces.
2. Refractory Coatings
Characteristics: Coating materials made from refractory particles and binders; they enhance the refractory performance of linings and reduce heat loss.
Applications: Applied to the surface of linings to improve their fire resistance and service life.
3. Refractory Castables
Characteristics: A mixture of refractory particles and binders (such as cement or gypsum) that is cast into shape; used for repairing high-temperature furnace linings.
Applications: Used for repairing and reinforcing high-temperature furnace linings.
4. Ceramic Fibers
Characteristics: Fibrous materials produced from high-purity bauxite via high-temperature processing; they offer excellent thermal insulation and fire resistance.
Applications: Widely used for high-temperature thermal insulation and protection, such as insulation layers for kilns and thermal piping.
5. Unshaped Refractory Materials (Monolithic Refractories)
Characteristics: Mixtures composed of refractory aggregates, powders, binders, and sometimes additives; they can be used directly or after mixing with an appropriate liquid.
Types: Furnace repair mixes, refractory ramming mixes, refractory castables (a broader concept here than item #3, encompassing various forms of unshaped refractories), refractory plastics, refractory mortars, refractory gunning mixes, refractory projecting mixes, refractory coatings (similar to item #2 but classified here as a type of unshaped refractory), lightweight refractory castables, etc.
Applications: Used for lining repairs, thermal insulation, and more in various high-temperature equipment.
III. Special Refractory Materials
1. Fused-cast refractories
Characteristics: Refractory products formed by melting raw material mixtures at high temperatures and casting them into specific shapes.
Applications: Used for specialized components in high-temperature equipment, such as blast furnace tapholes and steelmaking furnace mouths.
2. Carbonaceous refractories
Characteristics: Primarily composed of carbon materials; they feature high electrical conductivity and high-temperature resistance but are susceptible to oxidation in strongly oxidizing environments.
Applications: Widely used in electric arc furnaces and for lining high-temperature reactors.
3. Special refractories
Characteristics: A new class of inorganic non-metallic materials developed from traditional ceramics and conventional refractories, possessing unique physical and chemical properties.
Types: Includes non-oxide refractories such as silicon nitride-bonded silicon carbide bricks, as well as nitrides, silicides, sulfides, borides, and carbides.
Applications: Used for specialized components in high-temperature equipment and for specific applications in high-temperature environments, such as thermal protection systems for spacecraft and shielding materials for nuclear reactors.
In summary, there is a wide variety of refractory materials, each with its own unique composition, characteristics, and applications. When selecting a refractory material, the appropriate type must be determined based on the specific operating environment and requirements.