How to select refractory materials for atmosphere protective kilns

The core of selecting refractory materials for atmosphere-protected kilns is to match the atmosphere, temperature and material characteristics in the kiln, giving priority to ensuring material stability, corrosion resistance and heat preservation, and avoiding kiln body damage or product defects caused by improper adaptation of materials and environment.  Core principles for selection: Suitable atmosphere type: Different protective atmospheres (such as hydrogen, nitrogen, ammonia) have greatly different corrosive effects on refractory materials, and materials that are resistant to the corresponding atmosphere need to be selected accordingly.  Meet temperature requirements: Select materials with refractoriness and load softening temperature standards based on the maximum operating temperature of the kiln (such as 1200°C, 1800°C) to avoid deformation and collapse at high temperatures.  Compatible material characteristics: Avoid chemical reactions between refractory materials and materials, or the release of impurity-contaminated materials (such as low-impurity refractory materials required for precision ceramic firing).  Selection of refractory materials under different atmospheres Inert atmosphere (nitrogen, argon): high alumina bricks and mullite bricks can be used when the temperature is <1600°C; corundum bricks and zirconia bricks are preferred when the temperature is >1600°C. These materials have strong chemical stability and are not easy to react with inert gases.  Reducing atmosphere (hydrogen, carbon monoxide): Avoid using materials containing easily reducing components such as iron oxide and calcium oxide. It is recommended to use silicon carbide bricks, silicon nitride combined silicon carbide bricks, or low iron and high alumina bricks to prevent the material from being reduced and powdered.  Oxidizing atmosphere (air, oxygen-rich): Clay bricks and high alumina bricks can be used at medium and low temperatures (<1400℃); corundum bricks and chromium corundum bricks can be used at high temperatures (>1400℃), which have excellent oxidation resistance and longer service life.  Corrosive atmosphere (ammonia, halogen gas): Give priority to highly densified corundum-mullite bricks and silicon nitride bricks to reduce atmosphere penetration and corrosion, and avoid using materials with excessive silicon content to prevent the generation of volatile compounds.  Reference for key performance indicators Volume density: The higher the density (volume density ≥ 3.0g/cm³), the more resistant it is to atmospheric penetration and erosion, making it suitable for highly corrosive scenarios.  Thermal shock stability: Kilns that frequently heat up and cool down need to choose materials with good thermal shock stability (such as silicon carbide bricks) to avoid cracking and peeling.  Normal temperature compressive strength: ≥30MPa, ensuring the structural stability of the kiln body, especially for large kilns or load-bearing parts.  Impurity content: Precision material firing kilns need to select low impurity materials (Fe₂O₃＜0.5%) to prevent impurities from migrating and contaminating the product.