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What is alkali resistant castable

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What is alkali resistant castable?

A castable refractory capable of resisting the erosion of alkali metal oxides (such as K2O and Na2O) at medium and high temperatures is called alkali resistant castable.The composition of this type of castable is similar to that of ordinary calcium aluminate cement bound castable. It is a mixture of alkali resistant refractory aggregate and powder, binder and admixture.

What are the categories of alkali resistant castable?What are their characteristics?

According to the different operating environment and conditions, alkali resistant refractory castables can be classified into light and heavy castables. Those with porosity greater than 45% are light alkali resistant castables, while those with porosity less than 45% are heavy alkali resistant castables.And the heavy material can be divided into medium temperature alkali resistant castable and high temperature alkali resistant castable.

The lightweight alkali resistant castable aggregates include alkali resistant ceramicite, clay porous clinker, waste porcelain material, high strength expanded perlite, etc., and calcium aluminate cement or sodium silicate for binding agent.Alkali resistant castable can be used high silicon refractory raw materials, such materials at high temperature will react with alkali metal oxides to form high viscosity liquid phase, forming a layer of glazed-like dense protective layer, to prevent the further penetration and erosion of alkali metal melt.Its chemical composition is Al2O3 30%~55%, SiO2 25%~45%.

The cement content of traditional alkali resistant castable is 25%~30%, and the water content is 20%~25%.Due to the destruction of cement cement structure at medium temperature (800~1000℃), the strength decreases greatly, which is only about 50% of the drying strength.Therefore, the introduction of ultrafine powder and appropriate and appropriate dispersant, cement dosage is reduced to 10%~20%, add water to 15%~20%.

The physical properties of typical low-cement lightweight alkali resistant castable are as follows: the temperature is 110℃, the bulk density is dried for 16h, the bulk density is 1.5~1.6g/cm3, the flexural strength is 3~6MPa, the compressive strength is 40~45MPa, and the rate of change after firing is -0.3%~ -0.5%.The temperature is 350℃, and the thermal conductivity is 0.4~0.5W/ (m·K).

The aggregates used for heavy alkali resistant castable are bauxite clinker, clay clinker, etc. The binder and alkali resistant powder are the same as the light alkali resistant castable.Its main chemical composition is: Al2O3 35%~60%, SiO2 35%~60%.Traditional heavy alkali resistant castable cement material 20%, add water 10%~15%;

Low cement type heavy alkali refractory castable cement content 5%~15%, add water 6.5%~7.5%.Heavy alkali resistant low cement refractory castable binder used calcium aluminate cement and silica powder (smoke) silicon, adding silica powder is helpful to improve the medium temperature of castable bonding strength, can also help in use castable lining body surface layer formed anti osmosis axis, its characteristic is medium temperature (1000 ~ 1200 ℃) after burning intensity and drying (110 ℃) strength when, after alkali erosion performance is good.

The physical indexes of typical low-weight alkali resistant refractory castables are as follows: the temperature is 110℃, the volume density is 2.20~2.59g/cm3, the flexural strength is 4~8MPa, and the compressive strength is 40~60MPa.After burning for 3 hours at 1100℃, the volume density was 2.20~2.40g/cm3, the bending strength was 6~10MPa, the compressive strength was 35~55MPa, the linear rate of change after burning was -0.3%~-0.4%, and the thermal shock stability (1100℃→ water cooling) was more than 20 times.The temperature is 350℃ and the thermal conductivity is 1.2~ 1.3w/(m·K).


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