Zircon brick for glass kiln

Pure zircon refractory bricks are refractory bricks with zircon as the main crystal phase, referred to as zircon refractory bricks, and are one of the important varieties of zircon-containing refractory materials.

1 Production of pure zircon refractory bricks

A Handling of raw materials

The raw material of zircon refractory bricks is selected zircon ore, referred to as zircon sand. Which contains about 90% of zircon.

The particle size of zircon concentrate is very fine and single, generally 0.1-0.2mm, and it is not suitable to make bricks directly.

To make pure zircon bricks with coarse particles, in order to adjust the particle size composition of the bricks and reduce the firing shrinkage, usually, the concentrate should be pre-calcined or melted at high temperature to make zircon clinker agglomerates. When calcining the clinker, first grind a part of the concentrate into fine powder, mix it with another part of the concentrate, and bond it with a temporary organic binder to make pellets or blanks. ) calcined to form a dense agglomerate. If alkali metal oxides or mineralizers such as MgO and CaO are present, it can also be calcined at a lower temperature above °C. Zircon sand begins to shrink from 900°C during calcination, and tends to stop at about 1350°C, and then expands instead, and shrinks sharply after 17000°C. The compactness of zircon concentrate sand agglomerates is improved after calcination, and the bulk density can reach more than 3.5g/cm3.

If pure betellite bricks are produced from fine powder, the concentrate can be directly calcined at 1450°C, loosened by quenching, and then ground.

B The production process of zircon bricks

Temporary binders, such as sulfite pulp waste liquid, dextrin and lignin, should be used in the production of pure zircon bricks. Also available are ethyl silicate, calcium alkyl acid and phosphoric acid, and water glass. If plastic refractory clay is used as a binder, the brick is easy to form and sinter, but it often causes the reduction of brick refractoriness and volume stability. The effect is especially pronounced when the amount of clay added to the ingredients is high.

In order to promote the sintering of pure zircon bricks, a small amount of CaO or Ca(OH)2, MgO or MgF2 and other mineralizers are often added to the ingredients. This admixture promotes the decomposition of ZrO2·SiO2 at high temperature, and forms a ZrO2 solid solution with ZrO2 and enters the glass phase, thereby promoting sintering.

When using pure zircon as ingredients, in order to ensure that the refractory brick has good properties and accurate shape, its particle size, the number of binders and additives must be precisely matched. For bricks containing all levels of coarse particles, multi-level particle ingredients are required, and the specific surface area and content 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 below, of which the number of microns should be the majority. When forming, according to the requirements for the density of refractory bricks, ordinary bricks are generally formed by extruding mud method and dry pressing method; for dense ones, mud pouring method is often used; for high-density ones, mud pouring and isostatic pressing methods are commonly used. The various components in the ingredients should correspond to the molding method. This pure zircon brick must be fired at a higher temperature. High-density bricks require higher temperatures, depending on the nature, content of fine powder in the bad body, and the type and quantity of mineralizers. The maximum firing temperature is generally around 1700 °C, which should be controlled so that the green body is sintered without significant sintering. deformation temperature, and corresponding to the holding time.

2 Properties and applications of pure zircon bricks

A Properties of refractory bricks

The ZrO2 content in pure zircon bricks is about 65%, which is almost entirely composed of zircon crystals, with only a very small amount of glass phase and free ZrO2. The true density is about 4.55g/cm3, the highest is 4.62g/cm3, the bulk density of ordinary bricks is 3.6-3.8g/cm3, and the apparent porosity is greater than 13%; the density of the dense ones is 3.8-4.0g/cm3, and the apparent porosity is For high-density refractory bricks, the bulk density is greater than 4.1g/cm3, and the apparent porosity is less than 1.0%.

Since this kind of refractory brick is almost entirely composed of zircon crystals, it contains a very small amount of glass phase, and the viscosity is also high at high temperature, so the refractoriness is very high, greater than 1825 ℃. The normal temperature compressive strength of the brick is 100-430MPa, the flexural strength is 17.6-.3MPa, and the softening temperature under load is above 1650℃, which increases with the reduction of flux mineralizer and the increase of firing temperature. up to 1750°C. Therefore, it is an excellent refractory brick with good wear resistance that resists the combined action of heat and heavy load at high temperature.

Because the thermal expansion of zircon is low, and the brick is fired at high temperature, the volume stability of the brick is high. From room temperature to 1400 ℃, the thermal expansion rate is only 0.5%. After 2h reburning at 1500℃, the residual shrinkage is only 0.04%~0.20%. Some bricks are refired at 1650°C without any residual shrinkage. High-density zircon bricks have poor thermal shock resistance when there are no coarse particles in them. It must be heated or cooled slowly during use. When the refractory brick is composed of multi-level particles, its thermal shock resistance is significantly improved.

This kind of refractory brick is not easy to be wetted and corroded by molten metal and slag, especially not easy to be wetted by aluminum and its alloys. Therefore, it has good corrosion resistance to slag, molten metal and molten glass. This is especially true of high-density bricks. For example, the degree of erosion by alkaline slag is only 1/3 of that of mullite bricks.

B Application of refractory bricks

Zircon bricks can be used as linings in ladle for continuous steel casting and other parts that are severely eroded by slag, and can also be used as casting holes for copper and aluminum smelting furnaces. In addition, 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 zirconium corundum brick and the silica brick.

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