Add zinc sulfate to the circulating water

Zinc sulfate is a cathodic corrosion inhibitor; typically, only about 2 mg/L of the cathodic corrosion inhibitor Zn2+ is required to provide some degree of corrosion protection for carbon steel.

It is meaningless to use it alone; it must be used in combination with other cooling water corrosion inhibitors. Zinc plays a synergistic role in this, enhancing the corrosion-inhibiting effect.

　②Precipitate film-type corrosion inhibitors: Carbonates, phosphates, and hydroxides of zinc, as well as carbonates and phosphates of calcium, are the most common precipitate film-type corrosion inhibitors. Since they are formed into a film through the reaction of zinc and calcium cations with carbonate, phosphate, and hydroxide anions in water within the cathodic region on the metal surface, they are also known as cathodic corrosion inhibitors. Cathodic corrosion inhibitors can react with relevant ions in water, and the reaction products deposit as a film at the cathode ； Taking zinc salts as an example, they produce Zn(OH)2 precipitates at the cathode site, which act as a protective film. The combined use of zinc salts with other corrosion inhibitors can enhance their effectiveness; in the presence of orthophosphates, Zn3(PO4)2 or (Zn,Fe)3(PO4)2 precipitates and adheres tightly to the metal surface, resulting in an even better corrosion inhibition effect. In practical applications, since calcium ions, carbonate ions, and hydroxide ions are naturally present in water, it is generally sufficient to add soluble zinc salts (such as zinc nitrate, zinc sulfate, or zinc chloride, which provide zinc ions) or soluble phosphates (such as sodium orthophosphate or polyphosphates that can be hydrolyzed into sodium orthophosphate, which provide phosphate ions) to the water. Therefore, these soluble zinc salts and soluble phosphates are commonly referred to as deposition film-type corrosion inhibitors or cathodic corrosion inhibitors. In this way, soluble phosphates (including polyphosphates) serve as both oxide film-type corrosion inhibitors and deposit film-type corrosion inhibitors. In addition, some phosphorus-containing organic compounds, such as organophosphonic acids (salts), organophosphates, and organophosphonic carboxylic acids, can also be classified as this type of corrosion inhibitor, which is probably related to their ability to be hydrolyzed into phosphates in the end. Since the precipitated corrosion inhibition film does not bond directly to the metal surface and is porous, it often fails to adhere properly to the metal surface, resulting in a corrosion inhibition effect that is inferior to that of oxide films.