Pure zircon brick is based on zircon, referred to as high zircon brick, which is one of the important types of zircon-containing refractories.

Production of high zircon bricks

(1) Raw material treatment. The raw material of zircon brick is selected zircon ore, referred to as zircon sand. Among them, the mass fraction of zircon is about 90%.

The particle size of zircon concentrate is very fine and single, generally 0.1-0.2mm, and it is not suitable to make refractory bricks directly. In order to obtain pure zircon refractory bricks with coarse particles, it is usually necessary to pre-calcinate the concentrate or melt it at high temperatures to make zircon clinker agglomerates.  and bonded with a temporary organic binder to make pellets or blanks, at 1500-1700 degrees (lower than the decomposition temperature of zircon) calcined into a compact mass. If alkali metal oxides or mineralizers such as MgO and Gao are present, they can be calcined at lower temperatures above 1050 degrees. Zircon sand begins to shrink from 900 degrees during calcination, and tends to stop shrinking when it reaches about 1350 degrees, and then expands instead, and shrinks sharply after 1700 degrees. 

If pure zircon products are produced from fine powder, the concentrate can be directly calcined at 1450 degrees, loosened by quenching, and then ground.

(2) Production of high zircon bricks. The production of pure zircon products should use temporary binders, such as sulfite pulp waste liquid, dextrin, lignin, etc., but also ethyl silicate, calcium alkyl acid, phosphoric acid, and water glass. If plastic refractory clay is used as a binder, the product is easy to form and sinter, but it often leads to a decrease in the refractoriness and volume stability of the product. Especially when the amount of clay added to the ingredients is high, the effect is particularly significant, as shown in Figures 6-3.

In order to promote the sintering of pure zircon products, a small amount of cocoa(OH)2 MgO or MgF2 and other mineralizers are often added to the ingredients. This additive promotes the decomposition of ZrO2•SiO2 at high temperature, forming a ZrO2 solid solution with ZrO2 and entering the glass phase, thereby promoting sintering.

When using pure zircon as ingredients, in order to ensure that the product has good properties and precise shape, its particle size, the number of binders, and additives must be precisely matched. For coarse particles containing all levels' products. Multi-level granular ingredients are required, and the specific surface area and amount of fine powder should be higher than ordinary refractory bricks, so as to facilitate the formation of dense green bodies and facilitate sintering. If the green body is completely composed of fine particles, the maximum particle size of the fine powder is usually less than 44 microns, of which the number of microns should be the majority. When molding, according to the requirements for the bulk density of the product, the ordinary products are generally formed by the mud extrusion method and the dry pressing method; the denser ones use the mud casting method; the high-density ones usually use the mud casting method and isostatic pressing method. The various components in the ingredients should correspond to the molding method. Pure zircon products must be fired at higher temperatures, and high-density products require higher temperatures. According to the nature and content of the fine powder in the bad body and the type and quantity of the mineralizer, the maximum firing temperature is generally about 1700 degrees, and it should be controlled so that the sintered surface of the bad body does not burn. The temperature at which significant deformation occurs corresponds to the holding time.

Properties and applications of high zircon bricks

(1) About 4.55g/cm3, up to 4.62g/cm3, the bulk density of ordinary products is 3.6-3.8g/cm3, and the apparent porosity is greater than 13%; the bulk density of dense refractory bricks is 3.8-40g/cm3, and the apparent porosity is about 5%; high-density Sexual products, the bulk density is greater than 4g/cm3, and the apparent porosity is less than 1.0%.

Since this product is almost entirely composed of zircon crystals, contains only a very small amount of glass phase, and has high viscosity at high temperatures, the refractoriness is very high, greater than 1825 degrees. The normal temperature compressive strength of the product is 100-430MPa, and the flexural strength is 17.8-763MPa. The softening temperature under load is greater than 1650 degrees and increases with the decrease of mineralizer and the increase of firing temperature, and the highest can reach 1750 degrees. Therefore, it is a refractory brick with excellent resistance to heat and heavy load at high temperatures and good wear resistance.

The thermal expansion of zircon is low, and it is fired at high temperatures, so the volume stability of the product is high. From room temperature to 1400 ℃, the thermal expansion rate is only 0.5%. After 2 hours of reburning at 1500 degrees, the residual shrinkage rate is only 0.04%~0.20%. Some products are refired at 1650°C without any residual shrinkage.

High-density zircon products have poor thermal shock resistance when there are no coarse particles in them. It must be heated or cooled slowly during use. Thermal shock resistance is significantly improved when the article is composed of multi-level particles.

Such products are not easily wetted and corroded by molten metal and slag, especially aluminum and its alloys. Therefore, it has good corrosion resistance to slag, molten metal, and molten glass. High-density products have better performance, for example, the degree of erosion by alkaline slag is only 1/3 of that of mullite products.

(2) Application of high zircon bricks.

Zircon products can be used as linings in steel ladles for continuous casting and other parts that are severely eroded by slag, and can also be used as smelters for copper and aluminum smelting furnaces. It can also be used in the place where the glass melting furnace is in direct contact with the molten glass and the upper structure, and as the isolation brick between the fused zircon corundum brick and the silica brick. For more information, please pay attention to China Refractory Brick Trading Network.