Alkali resistant castable

Castable refractories that are resistant to corrosion by alkali metal oxides (such as K2O and Na2O) at medium and high temperatures are called alkali refractory castable. The composition of this type of castable is similar to that of common calcium aluminate cement, which is a mixture of alkali resistant refractory aggregate and powder, binder and admixture.

According to the use environment and conditions are different, alkali resistant castable has light and heavy, the porosity of more than 45% for light alkali resistant castable, the porosity of less than 45% for light alkali resistant castable. And the heavy quality can be divided into medium temperature and high temperature alkali resistant castable.

The aggregate used for light alkali resistant refractory castable is alkali resistant ceramsite, clayey porous clinker, waste porcelain material, high strength expanded perlite, etc., and the binder is calcium aluminate cement or sodium silicate. Alkali resistant material can be used high silicon refractory raw material, this kind of material at high temperature will react with alkali metal oxide to form a high viscosity liquid phase, forming a layer of axial dense protective layer, to organize further penetration and erosion of alkali metal melt. Its chemical composition is generally: 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 damage of the cement structure at the medium temperature (800~1000℃), the strength of the cement decreased significantly, only about 50% of the drying strength. Therefore, ultramicro powder and appropriate dispersant can be introduced to reduce cement dosage to 10%~20% and add water to reduce to 15%~20%. The physical properties of typical low cement light alkali resistant refractory castable are as follows: temperature 110℃, drying for 16h, bulk density 1.5~1.6g/cm, flexural strength 3~6MPa, compressive strength 30~40MPa; The temperature was 1100℃. After 3 hours of firing, the bulk density was 1.4-1.5g /cm, the flexion strength was 6.0-6.5mpa, the compressive strength was 40-45mpa, and the rate of change of the line after firing was -0.3%~-0.5%. The temperature was 350℃ and the thermal conductivity was 0.4~0.5W/ (m·k).

The aggregate used for light alkali resistant refractory castable is alkali resistant ceramsite, clayey porous clinker, waste porcelain material, high strength expanded perlite, etc., and the binder is calcium aluminate cement or sodium silicate. The aggregate used for heavy alkali resistant refractory castable includes clay clinker, waste porcelain material, etc., the binder and alkali resistant powder are the same as light alkali resistant castable, and the binder generally uses calcium aluminate cement.

The alkali resistance mechanism of alkali resistant castable is that it reacts with alkali metal oxide at high temperature to form a high viscosity liquid phase, forming a layer of enamelized protective layer to prevent the penetration and erosion of alkali metal melt.

The heavy alkali resistant castable is mainly used in the kiln tail, kiln head, preheater, outlet and tuyere of calcined alumina rotary kiln and cement rotary kiln. The light alkali resistant refractory castable is mainly used for the top cover of the preheater of the rotary kiln, the tube body and the insulating lining inside the kiln. Alkali resistant castable can also be used in steel, nonferrous metals, glass, machinery, petrochemical and other industries on the alkali corrosion of industrial kilns.