Corundum vs Mullite Castable: Differences and Selection

Corundum vs Mullite Castable: Differences and Selection

1. The Fundamental Difference

Corundum castable uses fused or sintered corundum aggregate with α-Al₂O₃ as the main phase (Al₂O₃ usually above 85%); mullite castable uses mullite clinker or synthetic mullite aggregate with mullite (3Al₂O₃·2SiO₂) as the main phase (Al₂O₃ usually 70–80%). The mineral difference sets fundamentally different performance orientations: corundum is "hard," mullite is "stable."

2. Key Performance Comparison

Temperature rating: corundum castable reaches 1750–1800℃ max, mullite about 1650–1700℃. Strength: corundum CCS can exceed 90–100MPa, clearly higher than mullite. Thermal shock: mullite's lower expansion and inter-granular microcracks absorb thermal stress, giving notably better thermal-shock stability than corundum. Creep: mullite has high RUL and hot creep resistance for long-term load-bearing stability. Erosion: corundum is chemically stable with strong washout/slag resistance; mullite resists alkali attack better (corundum reacts with alkali).

3. Typical Applications

Corundum castable for: ladle working linings and slag lines (slag resistance), iron runners (washout), reheating furnace hot hearths (hot load), petrochemical cracking furnaces (high temperature), CFB wear zones (abrasion). Mullite castable for: hot stove pipes (thermal shock), glass regenerators and crowns (temperature cycling), ceramic kilns (thermal shock and creep), cement kiln inlet chambers (alkali), heat-treatment furnaces (long-term stability).

4. Selection Decision Points

Four steps: ① temperature—above 1700℃ choose corundum, below either works; ② thermal shock—frequent swings and rapid cycling favor mullite; ③ erosion—heavy slag/washout favors corundum, alkali environments favor mullite; ④ cost—mullite is generally more economical, prefer it when duty permits. Temperature cycling is the most common reason for mullite; slag/iron scouring the most common for corundum.

5. Composite Solutions

The two are not exclusive: corundum-mullite composite (Al₂O₃ ~80%) combines corundum hot strength with mullite thermal-shock resistance—the preferred compromise for hot thermal-cycling duty; layered designs of "corundum working layer + mullite backup" balance erosion and stability.

6. Conclusion

Corundum and mullite castables each have clear performance boundaries: choose corundum for ultimate temperature, strength and washout resistance; choose mullite for thermal-shock stability, creep resistance and alkali resistance. Lay out temperature, thermal shock, erosion and cost, and selection is straightforward. Henan Songrui New Refractory Materials Co., Ltd. supplies both with corundum-mullite composite customization.