The raw materials used in sintered zirconium corundum 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. When the raw materials are very pure Under certain conditions, the glass phase content can be less than 5%. Therefore, the physical-chemical basis for producing such products is mainly the solid-phase reaction between AI203 and ZrSi04.
There are three main types of products in this series:
① Reaction-sintered AZS products have a two-phase uniformly distributed microstructure composed of mullite and baddeleyite (including part of t-Zr02). This irreversible reaction is also called an in situ reaction. The reaction start temperature range is 1370-1420°C
②Recombination AZS products are made of electrofused AZS as raw material through crushing, shaping and sintering.
③Zircon stone series products. This series of products belongs to the simplest process type in the generalized sintered AZS - fired with sintered or fused mullite or corundum or calcined bauxite coarse particles and zircon in any proportion, adding a small amount of bonded clay or other binding agents. become. The firing temperature determines whether the zircon particles are completely decomposed, slightly decomposed on the surface, or not decomposed at all. There is no decomposition of sintered zircon at 1650°C, but the surface in contact with A1203 will decompose when the temperature is less than 1500°C.
A1203-Zrsi04 solid phase reaction
In the Zr02-AI203-ZrSi02 system, the AI203-ZrSi04 connection is in a non-coexisting relationship, and the following reaction occurs between the two at about 1400°C:
3Al0:+2ZrSi0,--3Al0,·2Si0,+2Zr0
The reaction products are tetragonal ZrO2 and amorphous mullite. The latter is an important transition phase that tends to equilibrium at sub-solid temperature. Baddeleyite and mullite are obtained above 1450°C.
Preparation of sintered zirconium corundum bricks（sintered azs brick）
The key issue in the preparation process of sintered AZS products is
① Ensure that ZrSi04 and AI203 react completely and sinter densely to form uniform mullite-(corundum)-baddeleyite clinker with a glass phase content of no more than 5%.
②The alumina + kaolin added should comply with the composition of mullite.
③The particle size gradation of the product is reasonable to ensure the maximum packing density
④ The product is fully fired to obtain the ideal microstructure.
It is quite difficult to produce high-quality sintered AZS products. In a sense, the strict requirements for controlling the process flow are no less stringent than those for cast products.
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