A Synergistic Effect between Stearic Acid and (+)-α-Tocopherol as a Green Inhibitor on Ferritic Stainless Steel Corrosion Inhibition in 3.0% NaCl Solution

Abstract

The synergistic inhibitory effect of stearic acid and (+)-α-tocopherol (E307) as a green inhibitor within a highly hydrophobic layer on the corrosion of low-carbon ferritic stainless steels was investigated in 3.0 wt% NaCl solution at 25 °C, focusing on long-term immersion tests. For a broader characterisation of the surface properties, especially the modified surfaces, of the samples used, the following methods were chosen: SEM was used to investigate the surface morphologies, the water contact angle to examine the wettability, while the corrosion resistance was investigated by potentiodynamic measurements and electrochemical impedance spectroscopy. The inhibition efficiency for modified ferritic stainless steel surfaces reached more than 99% after 1 h of immersion and remained the same after 5 days immersion testing when the surfaces were modified with (SA + 2.0 wt% E307) and more than 97% with (SA + 0.5 wt% E307) under the same test conditions.

Flower-like Superhydrophobic Surfaces Fabricated on Stainless Steel as a Barrier against Corrosion in Simulated Acid Rain

“…The contact angle of a liquid droplet is a suitable means of describing the wetting properties of a surface. In our previous research, it has already been shown that hydrophobic layers formed in this way can be classified as highly hydrophobic layers, with contact angle values close to 150° (so-called superhydrophobic layers) [ 26 , 27 , 28 ]. The CA values after prolonged exposure and whether the basic structure of these layers changed after 120 h of immersion in corrosion medium (simulated acid rain) were the main objective of the contact angle measurements and taking SEM photos.…”

“…The CA values after prolonged exposure and whether the basic structure of these layers changed after 120 h of immersion in corrosion medium (simulated acid rain) were the main objective of the contact angle measurements and taking SEM photos. In our previous work, the change in morphology of these coatings on the same material was observed after prolonged exposure to 3% NaCl [ 27 ]. Therefore, the surface wettability of the coatings was determined by measuring the contact angle of the water (CA), spreading 5–8 drops over the entire surface to obtain reliable CA values.…”

“…In other words: What is no longer usable in a certain area (due to an expiration date-food supplements) does not have to be thrown away, but can be a valuable raw material that can be used for other purposes, i.e., “every waste can be a raw material”. In the field of green protective coatings or green corrosion protection, much research has been performed on the incorporation of vitamins as potential green inhibitors in quite aggressive media on various metallic materials [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ]. Among the water-soluble vitamins, there are studies showing the great potential of vitamin C and a wide range of B vitamins as corrosion inhibitors for various metallic materials.…”

“…The great potential of green corrosion inhibitors can be attributed to the group of fat-soluble vitamins, which includes vitamin E ((+)-α-tocopherol, E307). Vitamin E is fat soluble, which characterises it as a non-polar substance, and gives it the ability to participate in the formation of hydrophobic layers or superhydrophobic surfaces that can provide excellent corrosion protection [ 26 , 27 , 28 ]. Superhydrophobicity is an effect in which the surface roughness and chemical composition combine to form an unusually hydrophobic surface that repels water/electrolyte and forms a successful barrier that protects the surface from electrolyte penetration and corrosion reactions.…”

“…Under the same conditions of fabrication of superhydrophobic protective layers as described previously, layers with a hierarchical structure in the form of a true flower structure were formed on the surface of the SS AISI 410 s, as shown in Figure 1 . Moreover, a high inhibition efficiency of >99% was achieved again for the selected system when the as-prepared self-assembled superhydrophpobic layers were formed in an ethanol solution of SA with the addition of E307 [ 27 , 28 ].…”