The raw materials used for sintered zirconium corundum (AZS) bricks (hereinafter referred to as AZS bricks) are alumina and zircon. Generally, the ZrO2 content is controlled at 15%~30%. The main crystal phase components are mullite, corundum and baddeleyite. Under the condition of very pure raw materials, the glass phase content can be less than 5%. Therefore, the physical-chemical basis for the production of such products is mainly the solid phase reaction between Al2O3 and ZrSiO4.
There are three main types of this series of products:
① Reaction sintered zirconium corundum (AZS) bricks products are microstructures with two phases uniformly distributed, consisting of mullite and baddeleyite (containing some t-Zr02). This irreversible reaction is also called in-situ reaction. The reaction start temperature range is 1370~1420℃.
② Recombined zirconium corundum (AZS) bricks products are made of fused AZS as raw materials through crushing, forming and sintering.
③ Zircon-containing series products. This series of products belongs to the simplest process type in the generalized sintered zirconium corundum (AZS) bricks - sintered or fused mullite or corundum or calcined bauxite coarse particles and zircon in any proportion, with a small amount of bonding clay or other binders. The firing temperature determines whether the zircon particles are completely decomposed, the surface is slightly decomposed, or not decomposed at all. There is no decomposition of zircon sintered at 1650℃, but the surface in contact with Al2O3 will decompose at less than 1500℃.
Al2O3-ZrSiO4 solid phase reaction
In the ZrO2-Al2O3-ZrSiO2 system, the Al2O3-ZrSiO4 connection is a non-coexistence relationship, and the following reaction occurs between the two at about 1400℃:
3Al2O3 + 2ZrSiO4→3Al2O3・ 2SiO2 +2ZrO2
The reaction products are tetragonal ZrO2 and amorphous mullite, the latter is an important transition phase that tends to equilibrium at sub-solidus temperature, and above 1450℃, baddeleyite and mullite are obtained.
Key issues in the preparation process of sintered zirconium corundum (AZS) bricks products
The key issues in the preparation process of sintered zirconium corundum (AZS) bricks products are:
① Ensure that ZrSiO4 and Al2O3 react completely, sinter densely, and form uniform mullite-(corundum)-badgestone clinker with a glass phase content not exceeding 5%.
② The added alumina + kaolin should conform to the composition of mullite.
③ The particle size of the product is reasonably matched to ensure the maximum packing density.
④ The product is fully sintered to obtain an ideal microstructure.
It is difficult to produce high-quality sintered zirconium corundum (AZS) bricks products. In a sense, the strict requirements for controlling the process flow are no less than those for molten cast products.
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