Aluminum magnesia spinel castables are refractory materials primarily composed of corundum, super-grade bauxite clinker, fused or high-purity magnesia, and alumina-magnesia spinel, using low-cement technology.
Magnesium aluminate spinel castable is a high-performance refractory material made with magnesium aluminate spinel (MgAl₂O₄) as the main raw material, combined with aggregates, a matrix (binder + fine powder), and additives. Its properties integrate the alkali resistance of magnesia-based materials with the high-temperature and acid resistance of corundum (alumina), making it suitable for complex industrial environments involving high temperatures, strong corrosion, and frequent thermal cycling.
The raw materials used in aluminum magnesia spinel castables are typically selected from premium-grade refractory sources. Particle size distribution and the maximum particle size of aggregates are scientifically designed according to the thickness of the working lining, such as in steel ladles.
Core Composition and Structure
Aggregate
Magnesium Aluminate Spinel Particles:
The main crystal phase is MgAl₂O₄, typically with a content ≥60%. Based on purity and synthesis method:
Pre-synthesized spinel: Produced via high-temperature fusion or sintering with high purity (MgO + Al₂O₃ ≥90%) and a stable structure.
In-situ synthesized spinel: Formed during construction through the reaction of magnesia and alumina raw materials. It is more cost-effective but requires strict control of reaction conditions.
Auxiliary Aggregates:
Corundum (Al₂O₃) or magnesia (MgO) is often added to improve high-temperature or alkali resistance.
Matrix
Binders:
Include calcium aluminate cement, phosphates, silicates, and micro powders (e.g., silica fume), which bond the aggregates and provide strength at medium and low temperatures.
Fine Powders:
Spinel micro powder, corundum micro powder, silica fume, etc., fill pores and improve density and impermeability.
Additives
Dispersants, water reducers (to enhance workability), explosion-proof fibers (e.g., metal fibers to prevent cracking during curing), and anti-spalling agents (to improve structural stability at high temperatures).
Advantage
Excellent Erosion Resistance
Strong Alkali Resistance:
Spinel shows significantly greater resistance to alkaline slag erosion (e.g., CaO, MgO in steelmaking slags) than corundum-based materials, making it ideal for alkaline environments in metallurgy.
Acid Resistance:
When combined with corundum, it can also withstand acidic gas erosion (e.g., SO₂, CO₂), making it suitable for kilns in the chemical industry.
High-Temperature Stability and Thermal Shock Resistance
High-Temperature Resistance:
Service temperatures range from 1500–1700°C, outperforming ordinary magnesia-based materials (e.g., magnesia sand tends to sinter and harden).
Thermal Shock Resistance:
Spinel has a low thermal expansion coefficient (~7.6×10⁻⁶/°C), and the matrix's micro-crack structure helps relieve thermal stress. This makes it suitable for kilns with frequent start-stops (e.g., blast furnaces, glass kilns).
High Strength and Wear Resistance
Compressive strength at room temperature ranges from 60–120 MPa (higher than conventional castables).
Strength retention at high temperature (1400°C) is ≥70%.
Excellent erosion resistance, applicable to iron troughs and cement kiln cyclones.
Convenient Construction and Maintenance
The castable can be molded on-site, making it adaptable to complex geometries (e.g., elbows, cones).
Localized damage can be repaired without replacing the entire lining.
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Physical and Chemical Specifications
|
Grade / Specifications |
FMA-70 |
FMA-75 |
HMA-65 |
GMA-90 |
|
|
Chemical Composition (%) |
Al2O3 ≥ |
70 |
75 |
65 |
90 |
|
MgO ≥ |
10 |
10 |
28 |
5 |
|
|
Bulk Density (g/cm3) ≥ |
110℃ x 24 hr |
2.70 |
2.80 |
2.65 |
3.00 |
|
Linear Change (%) |
1000℃ x 3 hr |
0+0.3 |
0+0.3 |
0+0.3 |
0+0.3 |
|
1500℃ x 3 hr |
0+1.5 |
0+1.5 |
0+1.5 |
0+1.5 |
|
|
Crushing Strength (Mpa) ≥ |
110℃ x 24 hr |
40 |
45 |
30 |
60 |
|
1000℃ x 3 hr |
50 |
60 |
50 |
80 |
|
|
1500℃ x 3 hr |
70 |
60 |
75 |
100 |
|
|
HMOP Hot Modulus of Rupture (Mpa) ≥ |
110℃ x 24 hr |
6 |
7 |
6 |
8 |
|
1000℃ x 3 hr |
7 |
7 |
8 |
11 |
|
|
1500℃ x 3 hr |
9 |
9 |
11 |
>11 |
|
|
Classification Temperature (℃) |
1500 |
1600 |
1600 |
1650 |
|
Features
Aluminum magnesia spinel castables exhibit the following key features:
High Temperature Resistance:
Capable of withstanding extreme heat.
Strong Resistance to Structural Spalling:
Maintains integrity under thermal stress.
Chemical Erosion Resistance:
Resists corrosion from steel slag and other aggressive agents.
Thermal Shock Resistance:
Withstands rapid temperature changes.
Non-wetting to Molten Steel:
Prevents molten steel adhesion.
Erosion Resistance:
Resists wear and abrasion.
These characteristics make them widely used in steel ladles, where they are also referred to as ladle castables. Their excellent performance includes strong resistance to erosion, corrosion, and spalling, combined with high wear resistance and thermal shock stability.Additionally, aluminum magnesia spinel castables offer high cost-effectiveness and long service life, making them a preferred choice in industrial applications.
Application
| Sector | Application site | Matching Performance Requirements |
| Metallurgical industry | Converter linings, electric furnace roofs, blast furnace trenches, ladle slag lines | Resistance to alkaline slag, thermal shock, and wear |
| Building materials industry | Cement kiln firing zones (alkaline environments), glass kiln regenerators | High temperature resistance, alkali dust resistance, and thermal shock stability |
| Chemical & Energy | Coal gasifiers (CO₂/H₂O corrosion), waste incinerator linings | Resistance to both acidic and alkaline corrosion and high-temperature gas erosion |
| Non-ferrous metals | Aluminum smelters (Na₂O erosion), copper slag lines | Resistance to metal oxide erosion and structural stability at high temperatures |
Construction and Maintenance Points
Baking Process
A stepped heating curve must be followed.
Low-temperature stage (<300°C): Slow removal of free water.
Medium-temperature stage (500–800°C): Activation of binders.
Rapid water discharge can cause cracking and must be avoided.
Key Selection Criteria
Spinel Type:
Pre-synthesized spinel: For high-erosion environments.
In-situ synthesized spinel: For medium-temperature conditions with cost constraints.
Binder Selection:
Magnesia-based binders: Best for alkaline environments.
Phosphate binders: Suitable for acidic environments.
Construction Control
Mixing: Minimum 5 minutes to ensure uniform dispersion of aggregates and matrix.
Vibration: Continue until surface bleeding appears to eliminate air pockets.
Environmental Conditions:
In winter: Ensure ambient temperature ≥5°C and apply insulation.
In summer: Use shading or other cooling methods; initial setting time is <30 minutes.
Conclusion
Combining alkali resistance, corrosion resistance, thermal shock stability, and high strength, aluminum magnesia spinel castables have become the preferred materials for high-temperature, alkaline environments in industries such as metallurgy and building materials. Their core value lies in effectively balancing erosion resistance and thermal shock performance-overcoming the rapid erosion problem of traditional corundum materials in alkaline environments. These castables are a critical technical solution for the long-life design of modern industrial kilns.
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