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(1) Hydrochloric acid hydrochloric acid (HCl) is an aqueous solution of hydrogen chloride gas and is a strong acid. Pure hydrochloric acid is a colorless, transparent solution. Industrial hydrochloride containing impurities (typically containing iron ions) and yellow. Commercially available hydrochloric acid has a concentration by weight of 31-37% and a density of 1.19. Hydrochloric acid has a strong volatile and pungent odor. When using, pay attention to protection or add anti-fogging agent. Hydrochloric acid is the most commonly used solution for removing scale and rust. When chemical cleaning, the concentration of hydrochloric acid used is 5-15%, generally not more than 25%, otherwise the corrosion rate is accelerated, which is unfavorable to equipment and vehicles. Because hydrochloric acid has strong cleaning ability, high speed and reasonable price, it is widely used, especially for removing calcium oxide-containing iron oxide scale.
(2) Sulfuric acid sulfur trioxide is dissolved in water to form sulfuric acid (H 2 SO 4 ). Pure concentrated sulfuric acid is a colorless oily liquid with a concentration of 98.3%. The density of sulfuric acid is 1.84, which is a binary active and strong acid. Industrial sulfuric acid contains impurities and is light brown. Concentrated sulfuric acid has strong water absorption and oxidation, no odor, and can be dissolved in water in any proportion. The concentration of commercially available concentrated sulfuric acid is 98%, and the concentration of sulfuric acid in industrial cleaning is 5-15%, which is effective for removing iron scale. However, due to its low volatility, it must be heated to a certain temperature to effectively descale. In addition, sulfuric acid having a concentration of 98% is sometimes used together with other acids such as nitric acid to remove biofouling such as coke scale and seaweed organisms. Sulfuric acid is dangerous to the human body and equipment. When diluting, add acid to the water and stir it. Do not add water to the acid to prevent splashing.
(iii) Nitric acid nitrate (HNO 3 ) is a strong oxidant. Pure nitric acid is a colorless liquid with a density of 1.50. Industrial concentrated nitric acid often has a yellow color, violently emits smoke in the air, and absorbs water, and the general concentration is 66-70%. Concentrated nitric acid is soluble in water and can be diluted to different concentrations. Conventional corrosion inhibitors, detergents and other additives in nitric acid is not stable enough, and therefore not suitable for carbon steel and copper alloys. It has a passivating effect on iron and can slow down corrosion.
(D) phosphoric acid, phosphoric acid (H 3 PO 4) is pentavalent phosphorus oxyacid pure material as a colorless prismatic crystal, a density of 1.834, usually as a colorless syrupy liquid. Phosphoric acid is very soluble in water and ethanol and is a medium strength acid. Its corrosivity becomes stronger with increasing temperature. It is also a strong complexing agent. Because of its weak ability to decompose dirt, especially for common calcium and magnesium salts , it is gradually eliminated in industrial and chemical cleaning. Sometimes, the rusted surface is washed with phosphoric acid at a concentration of 15-20% and a temperature of 40-80 ° C. The cleaning ability is poor at low temperatures.
(5) Hydrofluoric acid Hydrofluoric acid (HF) is an aqueous solution of hydrogen fluoride, which is a colorless liquid, easily soluble in water and is a weak acid. It emits smoke in the air and is highly corrosive and toxic. In use, it not only has the pickling ability, but also has a relatively high solvent-dissolving ability due to the complexation of fluoride ions. It also corrodes glass and ceramics. When used in combination with other acids, it can effectively decompose silicates, and can effectively remove sand and the like on castings . If no hydrofluoric acid, ammonium fluoride salt can be used to give hydrofluoric acid. In industrial cleaning, hydrofluoric acid (or ammonium hydrogen fluoride can be used with hydrochloric acid) can be used to dissolve insoluble silicon-containing soil.
(6) Aminosulfonic acid sulfamic acid (H 2 NSO 2 OH) is a strong acid, colorless and odorless crystal, which is not volatile, does not absorb moisture, and is relatively stable in a dry state. It has a density of 2.126 and is soluble in water. It can be used to remove calcium or other carbonates, but it is not effective for removing iron scale. This acid is stable at room temperature and decomposes at high temperatures, so it must be heated to about 60 ° C when used. It is the unique corrosion inhibitor may be used together with the specific metal galvanizing acid cleaning of stainless steel can.
(7) Citric acid citrate, also known as citric acid, scientific name 2-hydroxypropyltricarboxylic acid, is an organic acid. It has two forms: one is water, the other is anhydrate, the latter has a density of 1.542, is a colorless crystal or powder, has a strong acid taste, is soluble in water, ethanol and ether, and can be used alone to dissolve oxidation. Iron scale. When the pH is 3.5, it is effective for removing iron oxide. When the apparatus is washed with hydrochloric acid to leave an iron salt, a relatively thin citric acid solution is usually used for removal for passivation treatment. but. Its ability to dissolve scale is not as strong as other acids. After pickling, the waste liquid can be burned to reduce environmental pollution. Due to its high price, its application is limited.
(Viii) chromic acid, chromic acid (H 2 CrO 4) is chromium trioxide hydrate. It can only be present in the form of a solution or a salt, so chromic acid is sometimes referred to as chromium trioxide. Usually it is reddish brown, has a density of 2.70, is easily decomposed, has strong oxidizing properties, and is soluble in ethanol and ether. In some cases, 10% hot chromic acid can be used as an oxidant to assist in the removal of carbon deposits and certain sulfides (such as FeS 2 , which are insoluble in hydrochloric acid). However, it has been used very little because it is not suitable for discharge.
(9) Acetic acid acetic acid (CH 3 COOH), also known as acetic acid, colorless clear liquid, has a pungent taste, density of 1.049, soluble in water, ethanol and ether. Anhydrous acetic acid solidifies into ice at low temperatures, so it is often called glacial acetic acid. Ordinary acetic acid contains 36% pure acid, a colorless transparent liquid. Washed with acetic acid may be made of aluminum carbonate scale apparatus, it is ineffective clearance of the dissolved iron.
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