Surface analytical characterization of passive iron surface modified by alkyl-phosphonic acid layers

Organic corrosion inhibitors: where are we now? A review. Part IV. Passivation and the role of mono- and diphosphonates

“…The authors believe that the iron oxide/hydroxide is partially transformed into iron phosphonate, as indicated by the change in morphological homogeneity detected by AFM. Later, supplementing the studies of CEMS with the XPS method, the authors of [18] proved the presence of a phosphonate layer with a thickness of about a monolayer on the passive iron surface. It was shown that in an aqueous 0.1 M NaClO 4 solution the value of R p is higher than 70 kOhm·cm 2 and the protective effect Z is higher than 98%.…”

“…This is indicated by the results of measurements of static , XPS, AFM, and reflective absorption IRS. A long-term stability study showed the excellent stability of the SAMs formed by APhC [12][13][14][15][16][17][18] in up to 30 days in acidic, neutral and saline solutions and in up to 7 days in dry heating mode. Partial breakdown of the monolayer was observed in the alkaline medium, especially for shorter chain lengths.…”

“…APhC 18 attracted considerable interest due to the ability to form strong covalent bonds with oxides of various metals, as well as compact adsorption films due to van der Waals forces between the long alkyls of its molecules. Furthermore, having a molecule length of 2.2 nm, APhC 18 is well packed into self-organizing bilayers (SOB) [29].…”

“…The first of these includes works in which the protective properties of APhs with a relatively small alkyl length, C 7 -C 10 , were studied, which made it possible to obtain their thin layers, including SAMs, in aqueous solutions [16][17][18][19][20][21][22][23][24][25][26]. In the second group more hydrophobic monophosphonic compounds were studied, mainly octadecylphosphonic acid (APhC 18 ), that cannot be applied from aqueous solutions [27][28][29][30][31][32][33]. The APhs from the first group adsorbed from aqueous solutions form protective layers on iron surface, which can suppress the dissolution of the metal and stabilize its passive state.…”

“…Raman et al [31] noted that, despite the extensive use of APh in industry, the features of the mechanism of their interaction with steels are not sufficiently understood. They used FTIR and XPS in the study of SAM formed in 1 mM solutions of APhC 18 or APhC 8 in tetrahydrofuran (THF) on natural 316L steel oxide at room temperature. It was found that APhC 18 forms a well-ordered monomolecular layer that is not removed by washing with a pure solvent even if the steel is treated ultrasonically, but this washing allowed the removal of excess acid from the surface.…”