Is the lower the porosity of tabular corundum, the better?
The porosity of tabular corundum is not absolutely “the lower the better”; instead, it must be comprehensively judged based on the specific application scenario and core performance requirements. Its level directly affects key indicators such as the material’s thermal conductivity, strength, and corrosion resistance, and requirements for porosity vary significantly across different scenarios.
1. First, clarify: What is the “porosity” of tabular corundum?
Tabular corundum is a refractory material made of high-purity α-alumina (Al₂O₃) sintered at high temperatures. It contains a certain amount of pores (including open pores and closed pores). Porosity usually refers to “volume porosity” — the percentage of pore volume in the total volume of the material — and is one of the core indicators for measuring the compactness of its microstructure.
2. Advantages of “low porosity”: In which scenarios is low porosity needed?
When the application scenario has high requirements for corrosion resistance, high strength, and low thermal conductivity (in some cases), tabular corundum with low porosity is more advantageous. Typical scenarios include:
- Iron and steel industry: Ladle and tundish lining bricks/castables
Molten steel and slag are highly corrosive. Low porosity means fewer “channels” inside the material, which reduces slag penetration and molten steel erosion, extending the service life of the lining bricks. At the same time, low porosity improves the material’s room-temperature and high-temperature strength, preventing spalling due to loose structure at high temperatures. - Non-ferrous metal smelting: Refining furnace and electrolytic cell linings
Molten non-ferrous metals (e.g., aluminum, copper) and electrolytes are prone to penetration. Low porosity reduces the risk of “penetration corrosion” and enhances the material’s thermal shock resistance (minimizing thermal stress concentration caused by pores). - High-temperature kilns: Refractory bricks for high-temperature firing zones
Low-porosity materials have higher compactness, can withstand high-temperature loads above 1700°C, and reduce volume shrinkage at high temperatures (low re-firing shrinkage), ensuring the structural stability of the kiln.
3. Necessity of “high porosity”: In which scenarios is low porosity unsuitable?
When the application scenario requires thermal shock resistance, thermal insulation, and air permeability, excessively high compactness (too low porosity) becomes a disadvantage. In such cases, tabular corundum with medium to high porosity is preferred:
- Scenarios requiring high thermal shock resistance: Kiln doors and parts subject to rapid heating/cooling
Low-porosity materials have high thermal conductivity. During alternating hot and cold cycles at high temperatures, large temperature differences between the interior and exterior easily generate huge thermal stress, causing the material to crack. In contrast, medium to high porosity (usually 15%-25%) can “buffer thermal stress” through pores, improving thermal shock resistance (e.g., lining bricks for the quenching zone of ceramic kilns). - Thermal insulation scenarios: High-temperature kiln insulation layers
Pores (especially closed pores) block heat transfer. Tabular corundum with high porosity (often compounded with lightweight aggregates) has lower thermal conductivity and better insulation performance. Using low-porosity materials would lead to rapid heat dissipation from the kiln and increased energy consumption. - Scenarios requiring air permeability: Filter materials and permeable bricks
In applications such as non-ferrous metal melt filtration and molten steel stirring by gas injection, the material needs a certain level of air permeability. At this time, porosity must be controlled within a reasonable range (e.g., 20%-30%) to ensure fluid passage without leakage. Low porosity would directly block the air-permeable channels.
