Phosphate‐Based Organic Molecules Interleaved with Layered Double Hydroxide: Unraveling the Roles of Host Cations and the Guest‐Inhibiting Effect in Aluminum Corrosion Protection

Abstract

The incorporation of 2-hydroxyethyl phosphate (2-HEP) into layered double hydroxide (LDH) galleries results in the formation of new organic-inorganic hybrid assemblies, subsequently studied as a functionalized filler with regards to their corrosion inhibition as an epoxy-based polymer primer coating of aluminum AA 2024. Hybrid layered assemblies as well as the concomitant conveivable processes that consist of the release of interleaved 2-HEP and the uptake of corrosive Clanions were studied by X-ray diffraction. From DC polarization experiments, it is demonstrated that the anodic corrosion inhibition of 2-HEP is not impeded when the molecule is intercalated in the LDH container despite the absence of

Amino Acid Interleaved Layered Double Hydroxides as Promising Hybrid Materials for AA2024 Corrosion Inhibition

“…For L ‐Cys intercalated into LDHs, the corrosion inhibition is weaker, and the corrosion currents are reduced by factors of three only for Mg 2 Al‐Cys and MgZnAl‐Cys (Figure 3, c). As observed previously,19 this suggests that the LDH sheets may affect the performance of an inhibitor, here, most probably because pH buffering and competing species with L ‐Cys decrease the overall protection at the metal surface. The E corr values for Mg 2 Al and MgZnAl are shifted weakly to cathodic potentials (–5 and –9 mV, respectively), whereas LiAl 2 ‐Cys exhibits significant anodic potential (+35 mV, Figure 3, B), which demonstrates the effect of the layer composition on the corrosion‐inhibition properties through the replacement of divalent Mg or Zn ions by monovalent Li ions.…”

“…The spectra were fitted by using a simple equivalent circuit (Figure 6) composed of a resistance linked to the electrolyte solution R e , a capacitance C c and a resistance R c linked with the coating itself, and a resistance R d and a capacitance C d linked with the oxide layer 19,25,57. From general considerations, one equivalent circuit should not be used for both scratched and scratch‐free coatings.…”

“…Such “smart” ion‐exchange ability was proposed with nitrate LDHs as chloride trappers or scavengers 18. Evidently, such processes are not efficient at the cathodic corroded zone, which is open to a large quantity of aggressive Cl – anions, but are rather relevant for crevice or filiform corrosion, in which no efficient electrolyte exchange occurs if the local pH is not too low to induce the LDH platelets to dissolve and buffer the confined damaged zone 19…”

Anticorrosive waterborne epoxy (EP) coatings based on sodium tripolyphosphate-pillared layered double hydroxides (STPP-LDHs)

“…In addition to the ability to hold the corrosive anions in their layered structures, LDHs are also capable of encapsulating and releasing (in the controlled manners) corrosion inhibitors, providing them with supplemental advantage for anticorrosion [15]. There are emerging reports on the corrosion resistance of coatings by using the ion exchange characteristics of hydrotalcite [16][17][18][19][20][21][22][23]. For example, the Zn 2 Al/-V 10 O 28 6− LDHs are able to release the decavanadate in the amide-cured bisphenol epoxy resin during the ion exchange reaction of capturing chloride [16].…”

“…For example, the Zn 2 Al/-V 10 O 28 6− LDHs are able to release the decavanadate in the amide-cured bisphenol epoxy resin during the ion exchange reaction of capturing chloride [16]. Intercalated species contain inorganic and organic substances, such as: MoO 4 2− , decavanadate, aniline, benzene derivatives, 2-mercaptobenzothiazolate anions, tripolyphosphates, vanadate 2-benzothiazolythio-succinic acid and 2-hydroxyethyl phosphate [16][17][18][19][20][21][22][23]. Among these, tripolyphosphates (TPPs), especially sodium tripolyphosphate (STPP), are readily available with low toxicity and insignificant environmental effects.…”