Several High Temperature Resistant Components in High Temperature Castable Refractory

In the working lining of various kilns, the kiln mouth and coal injection nozzle of the new dry-process cement kiln are subject to strong high-temperature seismic erosion and serious wear and tear, and high-quality uncertain refractory materials are required. Generally, high temperature castable refractory for cement kiln contains corundum, mullite, andalusite, silicon carbide minerals. Next, several high temperature resistant components of high temperature castable refractory will be analyzed.

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Corundum Components

Corundum is divided into sintered corundum and fused corundum. Among them, fused corundum is a product obtained by melting alumina or bauxite in an electric furnace and then cooling. The fused corundum has large grains, high density, low porosity and high hardness. The sintered corundum has small grains, many pores and small hardness, but it has good thermal shock resistance.

Generally speaking, corundum has good high temperature resistance and wear resistance, but its thermal shock resistance is poor, and its thermal conductivity is large, especially its alkali resistance is poor.

Mullite Components

Mullite is also divided into sintered and fused mullite. Among them, the performance of fused mullite is better.

Generally speaking, mullite has good high-temperature volume stability, high thermal strength, and good creep resistance. With moderate to high thermal shock resistance and low thermal conductivity.

Kyanite Mineral known as "Three Mineral Stones"

Andalusite is a member of the kyanite group of minerals. Kyanite mineral refers to three homogeneous heterogeneous minerals with the molecular formula Al2O3-SiO2: kyanite, sillimanite and andalusite. The common properties of these three minerals are high refractoriness, pure texture and good corrosion resistance. During the calcination process, they are transformed into mullite and high silica content substances, and accompanied by volume expansion, these three volume expansions are different. (Kyanite is 16% to 18%, andalusite is 3% to 5%, and sillimanite is 7% to 8%.)

Kyanite Mineral

Kyanite Composition

At 1300 ~ 1350 ℃, kyanite is transformed into mullite and cristobalite, with a volume increase of 18%. Due to the large expansion, the amount of kyanite incorporated is limited. The expansion caused by the transformation of kyanite can be used to counteract the shrinkage of the amorphous refractory, and the mullite produced can improve the thermal shock resistance of the refractory castable. However, cristobalite converted by kyanite is not conducive to thermal shock resistance.

At 1400 ° C, kyanite is transformed into mullite and high silica glass phases, with a positive volume change of 4%. Due to the small expansion, it is beneficial to increase the production of andalusite. The expansion caused by the andalusite transformation can offset the shrinkage of the unshaped refractory. The mullite produced can improve the thermal shock resistance of refractory castables. The difference is that the high silica glass phase produced by andalusite conversion has a lower coefficient of thermal expansion, which is very beneficial to improve the thermal shock resistance of the castable.

Sillimanite Composition

At 1500 ° C, sillimanite is converted into mullite with a volume change of 8%. Theoretically, the expansion produced by the transformation of sillimanite can offset the shrinkage of mullite produced by the indefinite refractory material, which is beneficial to improve the thermal shock resistance of the refractory castable.

Kyanite is used as an expansion agent for low-grade refractory materials, andalusite is used as an additive for high- and middle-grade refractory materials, and sillimanite is not suitable as an expansion agent for indefinite refractory materials due to the high conversion temperature.

Silicon Carbide composition

The characteristics of silicon carbide (SiC) are high hardness, high thermal conductivity, low expansion and high melting point, which can be oxidized. The high hardness of silicon carbide is used to improve the wear resistance of refractory materials. The low expansion and high thermal conductivity of silicon carbide are used for the thermal shock resistance of amorphous refractory materials. The characteristic that silicon carbide may produce a passive oxide fire to form an SiO2 layer is used to improve the anti-erosion performance of the refractory material.

RS High Quality High Temperature Castable Refractory Plant

These high temperature resistant components in high temperature castable refractory have different properties. Under different conditions of use, their performance is also different. High-quality high temperature castable refractory products can better serve the normal production of new dry process cement kilns. Get more information: https://www.hy-refractory.com/service/product_knowledge/high-temperature-castable-refractory.html.