Organo-metallic complex characterization formed when liquid epoxy-diamine mixtures are applied onto metallic substrates

Is gold always chemically passive?

“…Sharp needle-like crystals were previously observed [9,10,15,16,19] with Al and Ti modified IPDA, whereas modified DETA never crystallized (even after 3 h in contact with any metal). Fig.…”

“…In previous works [9][10][11], it was shown that the interphase formation was the result of the dissolution of the metallic surface layers, concomitant with the ion diffusion through the liquid prepolymer: when the oxide is exposed to a very basic environment (such as amine coating), the oxides and hydroxides disassociate exposing the underlying metallic ions (which are Lewis acids) [12]. Then the amine groups (which are Lewis bases) can easily react with the metallic surface.…”

“…The IPDA was the trans isomer, as expected, because the IPDA mixture was 75% of trans isomer and 25% cis isomer, and the geometry of trans was more suitable for crystallization. Only the trans isomer crystallized after modification by aluminium (no cis isomer was observed by X-ray diffraction), even if both cis and trans isomers react with aluminium and form organometallic complexes [10]. The aluminium atoms could not be enumerated, as their concentration was too low, but wavelength dispersive spectroscopy (WDS) and energy dispersive spectroscopy (EDS) analyzes confirmed their presence inside the crystal.…”

“…The overall performance of such systems depends on the substrate properties, the coating properties, and the interphase created between the polymer layer and the substrate. When epoxy-amine liquid mixtures are applied onto metallic substrates, amine chemisorption concomitant with metallic surface dissolution occur, leading to the organo-metallic complex formation [9][10][11]. When a metal oxide is exposed to a very basic environment (such as amine coating), the oxides and hydroxides disassociates exposing the underlying metallic ions (which are Lewis acids) [12] and then the amine groups (which are Lewis bases) can easily react with the metallic surface, leading to the metal-amine complexation [13,14].…”

“…The modified DETA never crystallizes, even after 3 h in contact with aluminium. The parameters determining the interphase formation were evaluated, and correlated to the change of mechanical properties observed by many authors [9,10,[15][16][17][18][19]21,[24][25][26].…”