Acid-resistant refractory castables are castable refractory materials that can resist corrosion in acidic media (nitric acid, hydrochloric acid, sulfuric acid, acetic acid, etc.) at 800~1200℃. It is made of water glass as a binder, acidic or semi-acidic refractory materials as aggregates and powders, and a small amount of accelerator. However, this type of monolithic refractory is not resistant to corrosion by alkali, hot phosphoric acid, hydrofluoric acid and high fatty acids. The raw materials for preparing this type of castable are abundant and low in price, so it is widely used in thermal equipment in metallurgy, chemical industry, petroleum, light industry and other departments.

Raw Materials for Preparing Acid-Resistant Refractory Castable

The aggregates used to prepare acid-resistant refractory castables mainly include silica, cast stone, wax stone, andesite, diabase, etc. The acid resistance (weight method, %) of several commonly used raw materials is: cast stone 98%, silica greater than 97%, clay clinker 92% ~ 97%, wax stone 92% ~ 96%, and andesite greater than 94%. The choice of raw materials should be determined according to the conditions of use. However, when using silica, it must be noted that quartz undergoes polycrystalline transformation when heated, and the volume changes and expansion will occur during the transformation process. Therefore, it is best to use waste silica bricks to replace part of the silica raw materials as aggregates. The powder materials for preparing this castable mainly use silica powder, cast stone powder, porcelain powder, high-siliceous clay clinker powder, etc. Among them, cast stone powder is the most acid-resistant powder material.

Binder for Acid-Resistant Refractory Castables

Binder water glass should use water glass with a higher modulus M to reduce the amount of Na2O brought in by water glass and improve acid resistance. Generally, water glass solution with a modulus of 2.6~3.2 and a density of 1.38~1.42g/cm3 is used. There are many compounds that can be used as water glass coagulants, including fluorine-containing compounds (such as alkali metal salts of fluosilicic acid, fluoboric acid, and fluotitanic acid), esters, acids (such as ethyl acetate), metal oxides (such as oxides of lead, zinc, barium, etc.), and carbonic acid (CO2). However, the most widely used is sodium fluosilicate (Na2SiF6), which is easy to use and easy to control the coagulation and hardening time.

Composition of Acid-Resistant Refractory Castables

The general composition of acid-resistant refractory castables is: 60% to 70% acid-resistant refractory aggregate, 30% to 40% powder, and 13% to 16% water glass solution with a density of 1.38 to 1.42 g/cm3. When sodium fluorosilicate is used as a hardening accelerator, its addition amount is 10% to 12% of the mass of the water glass solution.

Factors Affecting the Performance of Acid-Resistant Refractory Castables

1. The acid resistance of water glass combined with acid-resistant refractory castables is related to the acid resistance of the aggregates and powders used.

Relationship between the material and acid resistance of acid-resistant refractory castables

2. Acid-resistant refractory castables have good strength stability when soaked in acid. Generally, their compressive strength increases slightly with the extension of soaking time.

Effect of soaking time in acid on the compressive strength of castables

Application of Acid-Resistant Refractory Castables

Acid-resistant refractory castables are mainly used for anti-corrosion flue and chimney linings, acid storage tanks, pickling tank linings, nitric acid concentration tower linings, acid recovery furnace linings and other container linings corroded by acidic high-temperature gases.

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