Andalusite Bricks for Hot Blast Pipes & Their Mullitization Behavior

Blast furnace ironmaking is the world’s dominant process, where hot blast stoves supply 1200–1300°C air via pipeline networks (branches, mains, uptakes, bustle pipes).

Why Andalusite Bricks?

  • Low creep at high temperatures

  • Superior thermal shock resistance (>50 cycles)

  • Erosion/chemical corrosion resistance

Our Products:
✔ Full range of andalusite brick grades
✔ Certified performance (1450°C tested)
✔ Eco-friendly (raw material requires no pre-firing)

Item RH155 RH150 RH145 RH140 RH135
Al2O3  % ≥69 ≥65  ≥61 ≥57 ≥53
Fe2O3  % ≤1.0 ≤1.0 ≤1.2 ≤1.2 ≤1.5
TiO2  % ≤0.5 ≤0.5 ≤0.5 ≤0.6 ≤0.6
Open Porosity  % ≤20 ≤20 ≤20 ≤20 ≤20
Bulk Density g/cm3 2.55~2.70 2.50~2.65 2.45~2.60 2.40~2.55 2.35~2.50
Cold Crushing Strength MPa ≥55 ≥55 ≥50 ≥50 ≥40
Refractoriness Under Load 0,2 MPa °C ≥1700 ≥1700 ≥1650 ≥1600 ≥1520
Linear Change on Reheating % 1500°C×2h ±0.2 1500°C×2h ±0.2  1500°C×2h ±0.2 1450°C×2h ±0.2 1450°C×2h ±0.2
Creep Rate % 0.2 MPa 0~50h ≤0.8 1550°C ≤0.8 1500°C ≤0.8 1450°C ≤0.8 1400°C ≤0.8 1350°C

Andalusite is a high-quality natural refractory raw material that can be used directly without firing, which is significant for energy conservation and emission reduction. At high temperatures, andalusite undergoes a decomposition reaction:

  1. Primary Mullitization (1200–1600°C):

    2Al2SiO5→3Al2O3⋅2SiO2+SiO2+ΔV1

    • 20% volume expansion (glass phase reduces creep resistance)

This reaction is called the primary mullitization of andalusite. The complete decomposition temperatures are: Andalusite particles: 1450-1600°C; Andalusite fine powder: 1200-1300°C; The decomposition products of andalusite are: Mullite 3Al2O3·2SiO2; Silica-rich glass phase SiO2; Accompanied by volume expansion.

The content of silica-rich glass phase is related to temperature and impurity content. Under low impurity content, the silica-rich glass phase content is about 20%.

The silica-rich glass phase produced by andalusite decomposition adversely affects the material’s high-temperature performance, reducing creep resistance.

To mitigate this, alumina (Al₂O₃) is added to react with the glass phase and form mullite. This process is termed secondary mullitization:

  1. Secondary Mullitization (with Al₂O₃ additive):

    3SiO2+2Al2O3→3Al2O3⋅2SiO2+ΔV2

    • Compensates expansion (+7–8%), enhances creep resistance

The process principle of andalusite bricks for hot blast stoves is to utilize two-stage mullitization reactions of andalusite to achieve the product’s high-temperature performance.