What are the Roles of Zirconia Refractory Raw Materials in Refractory Materials?

Zircon and ZrO2 refractories made of zirconia-based refractory materials have excellent chemical resistance and high-temperature performance. For example, zirconia bricks are used for the slag line of steel drums, ZrO2 bricks are used for the nozzle holes of sliding nozzles, and ZrO2 quality sizing nozzles for horizontal continuous casting. At the same time, the zirconia-based raw materials are introduced into other refractory materials, and the phase change of ZrO2 is used to greatly improve the performance of the original materials, especially the thermal shock stability.

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The Effect of adding Zirconia Refractory Materials

Adding ZrO2 to refractory materials mainly has the following two functions.

①The main crystalline phase or the secondary crystalline phase is generated so that the material has special properties.

For example, the most well-known fused corundum brick. The composition of the #33 fused cast zirconia corundum brick produced in large quantities in the industry is near the eutectic point of the Al2O3-SiO2-ZrO2 ternary system, and the molecular formula is equivalent to 2Al2O3-SiO2-ZrO2, abbreviated as AZS fused cast brick. Its main crystalline phase is the eutectoid (Z+C) of oblique zircon and corundum, or zircon, corundum, and mullite (Z+C+M). The presence of the (Z+C) eutectoid makes the resistance of AZS bricks to chemical corrosion of glass solution 15 times stronger than that of high-alumina materials made by sintering. The independent component (Z+C) eutectoid is an important structural unit to maintain the stable handle of the AZS brick structure in the middle and late stages of the corrosion of the glass molten pool.

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In the iron and steel industry, the use of stable ZrO2's deoxidizing capacity and the use of stable ZrO2 bushings. The precipitation of oxides is suppressed, and the degree of clogging caused by the deposition of Al2O3 in the immersion nozzle for continuous casting is reduced by half.

②Modify the original materials

High alumina and alkaline refractory products have good chemical stability and high-temperature performance, but poor thermal shock stability. Adding ZrO2 to corundum bricks, high alumina bricks, magnesia bricks, etc., and the toughening effect of ZrO2 can significantly improve the thermal shock stability of these refractory products. The anti-stripping high alumina brick for cement kilns means adding zircon powder to the ingredients of the high alumina brick. After firing, due to the formation of many micro-cracks around the ZrO2 particles, the thermal shock stability (1100°C-water cooling) of this brick can reach more than 40 times. Good results have been achieved in the upper transition zone of the cement rotary kiln and the sidewall of the grate cooler. As early as the early 1930s, some people developed magnesia zirconia products, which have better thermal shock stability and resistance to iron furnace slag and open-hearth slag than magnesia bricks. After adding ZrO2, the strength of magnesia zirconia bricks is also higher than that of ordinary magnesia bricks. This product is expected to be used in cement rotary kilns to partially replace magnesia-chrome bricks to reduce Cr6+ pollution and protect the environment.

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How to Add Zirconia Refractory Raw Materials?

There are two ways to add zirconia refractory raw materials to refractory materials, the direct addition method, and the pre-synthesis method.

①Direct addition method

Usually, there are more requirements for the purity of refractory products, which can be directly made from zircon concentrate or plagioclase concentrate as raw materials or directly added to the raw materials of related refractory materials. Sintered zircon bricks for glass kilns are directly made from zircon concentrates containing more than 65% ZrO2. Fused AZS bricks are made of industrial alumina plus zircon concentrate as raw materials, or ZrO2 is directly added to alumina for casting. Anti-stripping high alumina bricks for cement kilns are made by adding zircon concentrate to high alumina ingredients.

②Pre-synthesis method

Using the pre-synthesis method, the zirconia-based raw materials need to be combined with other raw materials to synthesize the required minerals in advance. For example, in continuous casting refractories, in addition to high-purity ZrO2 products (sizing nozzles), the zirconia-containing raw materials used in other alumina-zirconia carbon refractories are mostly prepared by pre-synthesis and added. Such as synthetic AZS (electrofusion or sintering), AZT and AZTS, and other raw materials are added to the resin-bonded aluminum-carbon skateboard ingredients. The MgO-ZrO2 castables used in the slag line of the ladle uses pre-synthesized magnesia zircon sand as the raw material.

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