Alkali Resistant and Abrasion Resistant Castable

Alkali-resistant castable, a castable refractory that is resistant to attack by alkali metal oxides (such as K2O and Na2O) at medium and high temperatures, is called alkali-resistant castable. The composition of this castable is similar to that of ordinary calcium aluminate cement in that it is a mixture of alkali-resistant and fire-resistant aggregate and powder, binder and admixture. According to the different environment and conditions, the alkali and refractory castable can be divided into light weight and heavy quality, and the heavy quality can be divided into medium temperature alkali and high temperature alkali resistant castable.
(1) the aggregate used for light alkali resistant castable includes alkali resistant ceramsite, clay porous clinker, waste porcelain material, high strength expanded perlite, etc. Common calcium aluminate cement for binder. High silica refractory powder can be added to the substrate of castable material to make it react with alkali metal oxides at high temperature, forming an enamel-like dense layer on its surface to prevent further penetration and corrosion of alkali metal oxide melt. Chemical composition of ordinary lightweight alkali resistant castable: Al2O3 is 35%~65%, SiO2 is 25%~45%, volume density (drying) is 1.5~1.6g/cm3, other physical and chemical properties are shown in table 17-16.
(2) heavy medium temperature alkali-resistant castable aggregate includes high aluminum clinker, clay clinker, etc. Binder used calcium aluminate cement and silica powder (smoke) silicon, adding silicon oxide powder not only helps improve the medium temperature bonding strength of the castable, also helps in use castable lining body surface formation permeable formation, its characteristic is medium temperature (1000 ~ 1200 ℃) after burning intensity and drying intensity is quite after (110 ℃), alkali erosion performance is good. General heavy medium temperature alkali resistant castable chemical composition: Al2O3 is 45%~65%, SiO2 is 25%~35%, other physical and chemical properties are shown in table 17-16.

The alkali resistant refractory aggregates (aggregate and powder) used in heavy high temperature alkali resistant castable are fused spinel, chromium corundum, aluminum chromium slag, sintered or fused zirconium corundum and zirconium, etc. The binder is calcium aluminate cement with silica powder, or water glass solution as the binder.
Alkali-resistant castable is mainly used in places with alkali metal oxide and steam corrosion, such as the lining of cement rotary kiln kiln and outside decomposition cyclone separator, the lining of calcined alumina rotary kiln kiln, as well as the lining of steel, non-ferrous metals, glass, paper and other industries, industrial furnaces with alkali steam corrosion and their flue and smoke window.
Wear-resistant refractory castable
Castable refractories that resist the friction or erosion of high temperature solid materials or the airflow containing solid powders are called wear-resistant refractory castables. It is mainly used for lining of high temperature cyclone separator, circulating fluidized bed, and lining of heating furnace. This kind of castable has higher requirements for bending strength and compressive strength, so it is also called high strength refractory castable.
Wear resistant castable is composed of high strength refractory aggregate and powder, high strength binder and admixture. High strength refractory aggregate includes: fused alumina (white corundum, brown corundum, etc.), fused zirconium corundum, fused mullite, sintered alumina, fused alumina or clay, silicon carbide, etc., which can be selected according to the use conditions. There are two main systems of high strength binder:
(1) high-strength calcium aluminate cement with silica powder;
(2) phosphoric acid or aluminum phosphate plus hardener. Admixtures are mainly high - efficiency dispersants.
The granularity composition of wear resistant castable requires the closest possible packing. The ratio of general aggregate to powder is (65~70) :(30~35), or Andreassen's particle size distribution equation is used to obtain the particle size distribution coefficient q =0.26~0.35 for preparation.
Main performance index of the wear-resistant refractory castable for high temperature wear resistance, but there is no high temperature wear resistance measurement standard, only normal temperature wear resistance test method, as shown in the standard GB/T18301-2001. This method is to use special abrasion tester to determine, with black silicon carbide as A wear medium, using compressed air (pressure of 448 kpa) as the carrier, the particle size 36, black silicon carbide, by sandblasting pipe on the tested pieces of injection to A certain size, in the 450 s to 1000 g wear medium spray out, then determined by amount of wear test piece of A, A press type calculation of wear (cm3)
A = (M1, M2)/B = M/B
Where, B is the sample volume density, g/cm3; M1 is the sample mass before the test, g; M2 is the sample mass after the test, g; M is the sample mass loss, g. For wear-resistant refractory castable, it is generally required that the wear amount at room temperature is no more than 10cm3.
The wear-resistant refractory castable for circulating fluidized bed boiler in power plant is generally prepared with sintered high alumina and fused corundum, some are mixed with black silicon carbide, and the binder is high-grade calcium aluminate cement with silica powder (fume silicon). The physical and chemical properties of the castable are shown in table 17-17. The physical and chemical properties of the refractory castable for alumina suspension roasters are similar to that of the refractory castable for circulating fluidized bed boilers. The wear-resistant refractory castable used in the catalytic cracking unit of oil refining is fused or sintered white corundum (or sheet alumina) as the aggregate, and the high grade pure calcium aluminate cement with reactive alumina as the binder, the Fe2O3 content in the castable is required to be less than 0.05%. The castable for heating furnace steel groove is electrofused corundum (brown corundum or subwhite corundum) as aggregate, and the powder is composed of electrofused corundum powder, y-al2o3 powder, SiO2 powder, Cr2O3 powder (or zircon powder) and pure calcium aluminate cement. The castable shall be prepared into prefabricated blocks and roasted at high temperature (above 1500℃) for use. After a certain amount of SiC is added into the composition of this kind of pouring material, it can also be prefabricated into furnace sliding track brick, which has good wear resistance at high temperature.