Composition and Mineral Structure
Fused zirconium corundum brick is commonly known as white iron brick, also called corundum-zircon brick. The main chemical composition is Al2O3 50 to 70 percent, ZrO2 20 to 40 percent, with the remainder SiO2. The main mineral composition is baddeleyite (ZrO2), corundum (alpha-Al2O3), and glass phase. ZrO2 has a high melting point (about 2715 deg C), good chemical stability, and strong corrosion resistance to acidic and alkaline media, especially liquid glass.
Use in Glass Melting Furnaces
Fused zirconium corundum bricks are used in industrial furnaces such as glass melting furnaces. The used parts in glass melting furnaces include the upper pool wall, small furnace flat arch, small furnace stack, tongue arch, and parapet.
Consideration 1: Irregular Thermal Expansion
The expansion curve of fused zirconium corundum brick has an anomaly near 1000 deg C, where the internal ZrO2 crystal has a reversible crystal transformation with a large volume change. Brick containing ZrO2 should not be used where temperature fluctuates rapidly around 1000 deg C. When baking the kiln, the temperature change should not be too large between 900 and 1150 deg C, generally not exceeding 15 deg C per hour, and cold air should be prevented from blowing onto some parts.
Consideration 2: Shrinkage Holes
When casting molding, there are often shrinkage holes at the casting, where the brick body has more pores and poorer density. When building the glass melting pool wall, the shrinkage holes should be oriented toward the kiln. If the casting mouth faces outward, erosion to a very thin section can cause a glass leakage accident. When used in the upper flame space of the pool kiln, the casting mouth can be used outward to extend service life because the risk of running glass liquid does not arise there.
Consideration 3: Eutectic Behavior
Fused zirconium corundum brick and clay brick contact masonry can develop a eutectic phenomenon at 1300 deg C. When selecting refractories, avoid contact masonry between two materials with serious eutectic behavior; for example, silicon brick under fused zirconium corundum brick is most vulnerable to erosion.
Frequently Asked Questions
What is fused zirconium corundum brick? A refractory brick mainly composed of Al2O3, ZrO2, and SiO2, used in glass melting furnaces.
Why must temperature control be careful near 1000 deg C? ZrO2 undergoes a reversible crystal transformation with a large volume change near this temperature, which can cause cracking.
What are shrinkage holes? Casting defects with more pores and poorer density; they must be oriented correctly during furnace construction to avoid leakage.
