Surfactants Have Been Developed And Applied in The Corrosion And Rust

Surfactants have been developed and applied in the corrosion and rust prevention industry due to their ability to contain both hydrophilic non-polar groups and hydrophilic polar groups. Since most metal surfaces are charged, the hydrophilic groups will adsorb to the metal surface through physical or chemical action. When adsorbing, the hydrophilic groups will orient towards the metal, while the hydrophobic groups will position away from the metal. When the hydrophilicity of the surfactant is strong, it will have a stronger adsorption on the metal, but the dispersibility will be poor. If the hydrophobicity is strong, it will have good dispersibility, but the adsorption will be poor. Therefore, in different situations, the surfactant requires different hydrophilic-lipophilic balance (HLB value). Due to the adsorption of surfactant on the metal surface, on the one hand, it changes the nature of the interface and the distribution of charges on the metal surface, making the energy state of the metal surface more stable, increasing the activation energy of corrosion reaction (increasing the energy barrier), and slowing down the corrosion rate. On the other hand, the hydrophobic groups of the adsorbed surfactant form a hydrophobic protective film on the metal surface, preventing the movement of charges and substances related to corrosion, and reducing the corrosion reaction rate.
The charge state of the metal surface is particularly important for the adsorption of surfactants. The adsorption of surfactants on the metal surface mainly depends on electrostatic attraction and van der Waals force, of which the electrostatic attraction is more important. If the electrostatic potential (φ0=0) of the metal surface without charge distribution when the reference is taken as the electrode potential when the metal is in a corrosive medium, if the corrosion potential (φ1>φ0) of the metal is positive, it will be easily adsorbed by the anionic surfactant. If the corrosion potential (φ1-φ0) of the metal is negative, it will be easily adsorbed by the cationic surfactant. If the corrosion potential (φ1=φ Because the carbon chain grows, the inter-chain attraction is strengthened, and the shielding effect on the metal surface is enhanced, so it is more difficult for corrosion reactions to occur.
In addition to the physical adsorption described above, there is also chemical adsorption. This type of adsorption is monolayer adsorption and is irreversible. In addition, the double chains, triple chains, and π electrons on the benzene ring in surface-active agents can form chemical bonds with the metal to produce adsorption, thereby enhancing the metal's corrosion resistance.
In fact, the basic action mechanism of organic corrosion inhibitors and rust-preventing additives is the same. The molecules of the inhibitor form an adsorption film on the metal surface, blocking water or other corrosive media, thereby achieving the goal of preventing corrosion or rust.