Corrosion protection of metal equipment: the role of anti-corrosion coatings and influencing factors

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This post was last edited by Wang Wei2 on 2024-10-14 at 10:37. (1) Functions: a. Shielding function. The paint film prevents corrosive media from coming into contact with the material surface ； It blocks the path of the corrosion cell, increasing the resistance. 　 b. Corrosion inhibition. Certain pigments, or their reaction products with film-forming substances or water, can exert a corrosion-inhibiting effect on the base metal (including passivation). c. Cathodic protection effect. The electrode potential of the paint film is lower than that of the base metal; in a corrosion cell, it acts as an anode and “sacrifices” itself, thereby protecting the base metal (cathode). (2) Influence of coating film-forming substances The film-forming substances in anti-corrosion coatings exhibit chemical stability in corrosive media; their standards are related to the composition and chemical structure of these film-forming substances. Basically, it’s about whether it readily reacts with corrosive media under dry-film conditions or decomposes into small molecules in such media. Whether for preventing electrochemical corrosion or merely for providing isolation, the shielding effect of anti-corrosion coatings is very important; the shielding capability of the paint film depends on the structural pores of its film-forming substances and the pinholes in the coating. 　　The rates at which water, oxygen, and ions permeate through the paint film are different. The permeation rate of water is much higher than that of ions. Oxygen permeation is complex and highly dependent on temperature. After penetrating the paint film, water and oxygen can form a corrosion cell on the metal surface. Ions pass through the paint film in small amounts, so their direct effect on the base metal can be ignored; however, they increase the electrical conductivity of the paint film. 　　When the molecules in the film-forming substance have numerous functional groups, the paint film has few structural pores, and they can react with each other during the film formation process to create a highly cross-linked network structure, thereby enhancing the coating’s corrosion resistance. 　　The physical and mechanical properties of the paint film greatly influence the corrosion protection efficiency of anti-corrosion coatings. They are related to the molecular weight of the film-forming substance, its chain segments, side groups, etc. (3) Influence of pigments and fillers: In coatings, coloring pigments serve to impart color ； Body pigments are used to adjust the mechanical properties of the paint film or the flowability of the coating. For anti-corrosion coatings, in addition to the two types of pigments mentioned above, there are also pigments added for anti-corrosion purposes: one type is rust-inhibiting pigments that utilize their chemical properties to prevent metal corrosion ； Another category is flake pigments, which enhance the shielding properties of the coating through physical effects.