Chromium corundum castables are primarily made from high-strength refractory raw materials such as corundum and chromium oxide, with the addition of micro-powders. These materials belong to the composite corundum castable series and are classified as neutral refractory castables. They consist of coarse aggregates, fine aggregates, and powders mixed in specific proportions, along with precisely measured binders and additives.
These castables are suitable for casting and forming applications. During construction, binders, setting agents, and an appropriate amount of water are added to the mix, resulting in castables with excellent flowability. They offer a longer service life compared to traditional corundum castables.
Composition & Structure
Main Raw Materials
Chrome Corundum Aggregate:
Base material: Industrial alumina (Al₂O₃ ≥99%) blended with 5–15% Cr₂O₃, processed by high-temperature melting (above 2000°C) or sintering.
Main crystal phases: α-Al₂O₃ (corundum) and a small amount of chrome corundum solid solution (with dissolved Cr₂O₃). The dense crystal structure and increased lattice distortion enhance chemical stability.
Color: Varies from light red to dark red depending on Cr₂O₃ content.
Binders:
Includes calcium aluminate cement, phosphates (e.g., aluminum dihydrogen phosphate), silicates, etc., which provide low-temperature curing and high-temperature bonding.
Fine Powders:
Corundum micropowder, silica fume, chrome corundum micropowder, etc., are used to fill pores and improve density and strength.
Additives:
Dispersants, water reducers, and antioxidants (e.g., metallic aluminum powder) are added to enhance workability and high-temperature performance.
Structural Characteristics
The aggregates and matrix form a dense structure through ceramic bonding or eutectic bonding. This structure resists the formation of intergranular glass phases at high temperatures and provides strong resistance to slag penetration.
Advantage
High-Temperature Resistance
Service temperature: 1600–1800°C, which is higher than that of ordinary corundum castables (1500–1650°C).
Reason: Cr₂O₃ increases the liquidus temperature and inhibits the formation of low-melting compounds at high temperatures.
Erosion Resistance
Slag Resistance: Excellent resistance to acidic slags (e.g., silicate slags in glass kilns, sulfur-containing slags in chemical furnaces) and oxidizing atmospheres (e.g., FeO, VOx in steelmaking).
Mechanism: Cr₂O₃ reacts with acidic oxides to form high-melting-point chromates (e.g., Cr₂O₃ + SiO₂ → Cr₂Si₂O₇, melting point 1780°C), creating a dense protective layer.
Oxidation Resistance: In oxidizing atmospheres at high temperatures, Cr₂O₃ forms a stable protective film that prevents further oxidation of the internal Al₂O₃.
Thermal Shock Stability
With a low thermal expansion coefficient (~8×10⁻⁶/°C) and lattice distortion in the chrome corundum solid solution, thermal stress is reduced. This makes the material suitable for environments with frequent temperature fluctuations (e.g., batch kilns).
Mechanical Strength
Room temperature compressive strength: 80–150 MPa
Strength retention at 1400°C: ≥80%, with excellent erosion and wear resistance
Comparison with other castables：
| Material type | Main components | Advantageous performance | Typical Application Scenarios |
| Chrome corundum castables | Al₂O₃+Cr₂O₃ | Resistant to acid slag, oxidation, high temperature strength | Glass kiln, metallurgical acid furnace |
| Magnesium-aluminum spinel castables | MgAl₂O₄+Al₂O₃ | Good resistance to alkaline slag and thermal shock | Steel furnaces, cement kilns |
| Ordinary corundum castables | Al₂O₃(≥90%) | Wear resistance and high strength at medium–high temperatures | Cement kiln cyclone, heating furnace |
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Physical and Chemical Specifications
| Grade / Specifications |
GDC-1 |
GDC-2 |
GDC-3 |
|
|
Chemical Composition (%) |
Al2O3 ≥ |
90 |
93.5 |
96 |
|
Cr2O3 ≥ |
3 |
3 |
3 |
|
|
Bulk Density (g/cm3) ≥ |
110℃ x 24 hr |
3.05 |
3.10 |
3.15 |
|
Linear Change (%) |
1500℃ x 3 hr |
±0.5 |
±0.5 |
±0.5 |
|
Crushing Strength (Mpa) ≥ |
110℃ x 24 hr |
75 |
95 |
115 |
|
1500℃ x 3 hr |
85 |
105 |
125 |
|
|
HMOP Hot Modulus of Rupture (Mpa) ≥ |
110℃ x 24 hr |
10 |
12 |
14 |
|
1500℃ x 3 hr |
12 |
14 |
16 |
|
|
Classification Temperature (℃) |
1670 |
1690 |
1710 |
|
Application
Metallurgical Industry
Steelmaking Furnaces (e.g., tapping holes, ladle slag lines): Resist erosion from high-basicity slags (CaO-SiO₂-Al₂O₃ systems) and FeO.
Non-ferrous Metal Smelting Furnaces: Withstand corrosion from acidic slags containing sulfur or copper (e.g., copper/nickel smelting).
Glass Industry
High-Temperature Zones in Glass Kilns (e.g., melting zones, flow channels): Resist erosion by silicate melts and Na₂O vapor.
Advantage: Cr₂O₃ reacts with Na₂O to form a viscous Cr-Na silicate layer that blocks further penetration.
Chemical and Ceramic Industries
Chemical Furnaces: Ideal for processes involving acidic gases such as SO₂ and HCl.
Ceramic Sintering Furnaces: Perform well under oxidizing conditions and frequent thermal cycling.
Other High-temperature Fields
Used in environments such as waste incinerators and refractory testing furnaces where extreme corrosion and temperature resistance are required.
Construction and Precautions
Construction Key Points
Use a forced-action mixer and mix for at least 6 minutes to ensure even distribution of Cr₂O₃ aggregates and matrix materials.
Vibrate until surface bleeding occurs to prevent aggregate settlement, due to the high density of Cr₂O₃ (~4.0 g/cm³).
Baking Process
Follow a stepped heating process:
Low-temperature stage (<300°C): Evaporate free water slowly.
Mid-temperature stage (600–800°C): Promote binder sintering.
High-temperature stage (>1200°C): Develop ceramic bonding.
Avoid rapid heating or cooling to prevent stress cracking due to intergranular tension in Cr₂O₃.
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