Analysis of the stability of metal anticorrosive coatings on corrosive media.

The stability of anti-corrosion coating on corrosive media refers to the chemical neither decomposition of the medium nor harmful reaction to the medium;
most corrosion-resistant coatings are used only in neutral to slightly alkaline water-containing media and low polarity organic solvents. After strengthening and thickening the coating system, there is also a long-term resistance to strong corrosion media

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, water
water is the most commonly encountered corrosive medium, in addition to its own hydrolysis and osmosis damage to high-lying matter, but also with the existence of other substances to play a synergeous destructive effect.
water penetration of the coating is considered to be the process of attracting through adsorption, dissolution, diffusion and capillary.
adsorption and dissolution are related to the polar group and soluble components contained in the paint-based polymer, and diffusion and capillary attraction are related to the activity of the polymer chain, the perforation of the coating, and the leaching perforation.
soluble components include small molecular monomers, residual solvents, foreign contaminants, and polymer degradation. The perforation of the coating includes the pinholes of the coating and the pores that exist between and inside the polymer molecules. Among them, the pinhole comes from the unsatisfactory construction, and the pores determine the molecular structure, crosslink density and arrangement state of the polymer, which is inherent in the coating.
, coating penetration cannot be absolutely avoided.
, in addition to the selection of high-polymer types, reduce the content of polar substances, improve the quality of coating, pigment applications also have a great impact.
variety, dosing, dispersion and particle geometry of pigments can have a great impact on the water permeability of the paint film.
when the pigment in the coating is less than the critical pigment volume concentration (CPVC), water penetrates through the base material between pigment particles;
inert flaky pigments act as bezels in the coating and can delay the penetration of moisture into the paint film.
II, acid
inorganic acid on the coating's role is mainly to make the coating of some polar groups of high-concentration group hydrolysing, at the double bond to increase the reaction and isomerization, but also dissolve and decompose the pigments and additives in the coating, and ultimately make the coating lose protection.
organic acids accelerate the conduct of harmful reactions due to the swelling and dissolution of high-concentrations, which makes the erosion effect more intense.
, alkali
alkali solution mainly the role of hydrolysing, and with the acidic groups in the high concentration into salt, so that the coating is more hydro-hydropho shui, and even bubble softening.
4. The damage of the salt
salt solution is to increase the concentration of ions, and the penetration of ions causes the resistance of the coating to decrease, and some ions, such as chlorine and sulfate ions, also interfere with the role of corrosion-reprodulation pigments at the bottom of the paint film, promoting metal corrosion under the coating.
In terms of the stability of corrosion-resistant media, carbon chain polymers are better than hybrid polymers; hydrogen atoms on the chain are better replaced by fluorine and chlorine atoms (e.g. fluorine resins), and high saturation and low polarity are better than polar groups containing double bonds.
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