Corrosion inhibitors can be divided into two categories: one is inorganic compound corrosion inhibitors, which include metasilicate, phosphate, tungstate, borate, nitrite and molybdate , benzoate, etc. As an inorganic compound corrosion inhibitor, it can form a dense passivation film on the metal surface, which can block or prevent the hydrogen permeation and acid permeation of the metal. For example, adding 0.05 to 0.03 sodium metasilicate can prevent corrosion of aluminum parts. The other type is organic compound corrosion inhibitors, which are often used as anti-rust additives in antifreeze. Commonly used ones include triethanolamine, benzotriazole, mercaptobenzothiazole, organic phosphate, etc., which have good corrosion inhibition properties. For example, adding only 0.1 to 0.5 benzotriazole can prevent copper components from corrosion. corrosion. Metal components with different compositions require different corrosion inhibitors. Sodium nitrite has a good corrosion inhibitor effect on steel and cast iron, but it will cause pitting corrosion on solders. Triethanolamine, phosphates, and organic phosphates have good corrosion inhibitor effects on ferrous metals. , but corrosive to brass and copper; silicate is an excellent corrosion inhibitor for aluminum, but it is extremely easy to hydrolyze and form a large amount of flocculent precipitation. Although these single varieties of corrosion inhibitors are relatively low in cost, they are difficult to meet the performance requirements of antifreeze in many aspects. Today's commercially available antifreeze uses a compound formula of multiple corrosion inhibitors with synergistic effects, and the corrosion inhibition rate is very high. The corrosion inhibitors currently used in foreign patents are composed of a variety of corrosion inhibitors, and the corrosion inhibitor effect is very ideal. It is worth mentioning that benzotriazole and mercaptobenzothiazole are special corrosion inhibitors for copper and brass.