What is the principle of high temperature resistance of high alumina bricks?

The high temperature resistance of high alumina bricks mainly comes from their chemical composition, mineral phase composition, and microstructure design. The following is a detailed analysis of their high temperature resistance principle:

1、 High Al ₂ O ∝ content and crystal phase stability

The dominant role of alumina (Al ₂ O3)

The Al ₂ O3 content of high alumina bricks is usually above 48%, with first grade high alumina bricks reaching over 75%, and corundum products even exceeding 90%.

The melting point of Al ₂ O ∝ is as high as 2054 ℃, endowing the material with extremely high refractoriness (1750-1790 ℃).

When the content of Al ₂ O3 is greater than 71.8%, the high-temperature stable crystal phase changes from mullite (3Al ₂ O3 · 2SiO ₂) to corundum (α - Al ₂ O3), which has strong chemical inertness and significantly improved resistance to acid and alkali slag erosion.

The synergistic effect of mullite and corundum

Mullite forms a network structure, providing high-temperature strength; Jadeite crystals fill the gaps in the skeleton to enhance creep resistance.

The proportion of corundum phase in first grade high alumina bricks is high, and the softening temperature under load can reach above 1510 ℃, far superior to clay bricks.

2、 Microstructure optimization and additive technology

Reduce low melting point glass phase

Impurities such as Fe ₂ O3 and TiO ₂ can generate low melting point glass phases, reducing high-temperature strength. By using high-purity raw materials (such as fused alumina) and optimizing the ratio, the glass phase content can be reduced.

Application of functional additives

The "Three Stones" minerals (andalusite, kyanite, and sillimanite): transform into mullite at high temperatures, accompanied by volume expansion (kyanite expansion 16-18%), compensate for sintering shrinkage, and improve thermal shock resistance and creep resistance.

Silicon carbide (SiC) or graphite: enhances thermal conductivity, reduces thermal stress cracks, and improves slag penetration resistance.

Micro powder and high-pressure forming technology

Fill the pores with α - Al ₂ O3 micro powder (<1 μ m), and the apparent porosity can be reduced to below 15%, reducing the risk of slag infiltration.

Isostatic pressing (150MPa) and high-temperature sintering (1500-1600 ℃) promote densification, forming a grain direct bonding structure.

3、 Composite Structure and Process Innovation

Composite brick design

If sintered high alumina anti stripping brick (HF-80), the working layer (Al ₂ O ∝ ≥ 80%) is combined with the insulation layer, it can withstand high temperatures and reduce the cylinder temperature by 90-100 ℃, extending its service life.

Solid phase reaction and recrystallization

Solid phase reactions (such as the formation of spinel between MgO and Al ₂ O3) and recrystallization at high temperatures can optimize grain boundary structures and suppress high-temperature creep.

4、 Performance Shortcomings and Improvement Directions

Insufficient thermal shock resistance: Corundum has a high coefficient of thermal expansion and is prone to cracking due to sudden temperature changes. Improvement can be achieved by introducing microcracks (such as those generated by "three stone" phase transformation) or toughening with zircon.

Environmental trend: gradually phasing out chromium containing materials and shifting towards chromium free formulas (such as magnesium aluminum spinel).

summary

The high temperature resistance of high alumina bricks is essentially the result of the synergistic effect of high Al ₂ O3 crystal phase stability, micro densification, and functional additives. The future development direction includes higher purity raw materials, intelligent process monitoring, and the application of regeneration technology.