What are the formulations and applications of acid-resistant refractory castables?

Refractory acid-resistant castables are castable refractory materials capable of withstanding corrosion from acidic media (nitric acid, hydrochloric acid, sulfuric acid, acetic acid, etc.) at temperatures ranging from 800 to 1200°C. They are formulated using water glass as a binder, with acidic or acid-alkaline refractory materials serving as aggregates and powders, supplemented by a small amount of setting accelerator. However, these castables are not resistant to alkalis, hot phosphoric acid, hydrofluoric acid, or high-fat corrosion. Given the abundant and low-cost raw materials required for their preparation, they are widely used in thermal equipment across metallurgy, chemical engineering, petroleum, and light industry sectors.

Acid-Resistant Refractory Castable

1. The primary aggregates used for preparing acid-resistant refractory castables include silica stone, cast stone, wax stone, andesite, and diabase. The acid resistance (measured by weight, %) of several commonly used raw materials is as follows: cast stone 98%, silica stone greater than 97%, clay sinter 92%–97%, wax stone 92%–96%, and andesite greater than 94%. The selection of raw materials depends on the application conditions. However, when using silica, note that quartz undergoes a polycrystalline transformation during heating, causing volume changes (expansion). Therefore, it is advisable to replace part of the silica aggregate with waste silica brick material. The powder components for this castable primarily include silica powder, cast stone powder, porcelain powder, and high-silica clay sintered powder, among which cast stone powder is the most commonly used acid-resistant powder.

2. Water glass as the binder should be of higher modulus (M) to reduce the Na₂O content introduced by the water glass and enhance acid resistance. Typically, a water glass solution with a modulus of 2.6-3.2 and a density of 1.38-1.42 g/cm³ is used. Numerous compounds can serve as water glass accelerators, including fluorine-containing compounds (e.g., alkali metal salts of fluorosilicic acid, fluoboric acid, fluotitanic acid), esters, acids (e.g., ethyl acetate), metal oxides (e.g., lead, zinc, barium oxides), and carbon dioxide (CO₂). However, sodium fluorosilicate (Na₂SiF₆) is most widely used due to its convenience and ease in controlling setting and hardening times.

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

Acid-resistant refractory castables are primarily used for corrosion-resistant flue and chimney linings, acid storage tanks, pickling tank linings, nitric acid condensation tower linings, acid recovery furnace linings, and other containers exposed to acidic high-temperature gas corrosion.

Silica Ramming Mass