Characteristics and mechanism of corrosion inhibitors

Characteristics and mechanism of corrosion inhibitors

The research on the corrosion inhibition mechanism of corrosion inhibitors can be traced back to the beginning of the 20th century.

Table 6-2 Classification of application scope of some corrosion inhibitors

(1) The characteristics and mechanism of inorganic compound corrosion inhibitors

Inorganic corrosion inhibitors are mostly used in neutral media systems, which mainly affect the anode process and passivation state of metals

①Materials for forming passivation protective film are mainly compounds containing MeO ₄ ^n- type anions, such as K ₂ CrO ₄ , KMnO ₄ , Na ₂ MoO ₄ , Na ₂ WO ₄ , Na ₃ WO _4, etc.

② generating substances insoluble salts deposited film of polymeric phosphates , silicates , HC03 _.

③ active anionic mainly refers CI ^- , Br ^- , the I ^- , the HS ^- , SCN-, etc.

④Metal cations refer to metal ions Sn ²⁺ , Cu ²⁺ , Fe ²⁺ , Pb ²⁺ , A1 ³⁺ , Ag ⁺ and so on

(2) The characteristics and mechanism of organic compound corrosion inhibitors

Organic corrosion inhibitors mainly refer to those compounds containing unpaired electronic elements (such as O, N, S) and various chemical substances containing polar groups, especially substances containing amino groups, aldehyde groups, carboxyl groups, hydroxyl groups, and sulfhydryl groups.

At present, it is believed that the corrosion inhibition mechanisms of organic compound corrosion inhibitors mainly include adsorption mechanism, film formation mechanism and electrochemical mechanism

Most of the corrosion inhibitors that can form an adsorption film are organic

Many organic corrosion inhibitors containing nitrogen, phosphorus, sulfur, arsenic and other elements can form Onium ions with hydrogen ions in acidic aqueous solutions

Figure 6-1 Schematic diagram of monolayer adsorption on the metal surface

When such ions are adsorbed on the surface of the cathode, it is difficult for the hydrogen ions in the acidic medium to approach the metal surface for reduction, thus increasing the overpotential of the hydrogen ion reaction and slowing down corrosion

The compound categories of the elemental composition of various corrosion inhibitors in the acid solution are shown in Table 6-3

Table 6-3 Elemental composition and compound category of corrosion inhibitor in acid solution

Table 6-4 Organic corrosion inhibitors for pickling and circulating water

Related Links: Classification of Corrosion Inhibitors