Influence of cations on the corrosion inhibition efficiency of aminophosphonic acid

The iron/electrolyte interphase has been studied in the presence of NN-di(p hosphonomethyl)glycine (DPMG) inhibitor with or without the bivalent cation s. In electrochemical measurements, inhibition was assumed by the formation of a complex in the presence of DPMG. In situ atomic force microscopy prov ided direct insight into changes in the surface morphology at several hundr ed nanometres when topographical changes owing to the breakdown of the pass ive layer, and initiation of corrosion were monitored. Section analysis has revealed the degree of deterioration. Bivalent cations (Ba2+, Sr2+, Ca2+ a nd Zn2+) synergically improved the activity of DPMG, though the mechanism w as different. Barium, strontium and calcium ions in blends hindered the ano dic iron dissolution, while zinc ions influenced both the anodic and cathod ic processes. Composition of the surface layer was analysed by X-ray photoe lectron spectroscopy (XPS). The 2:1 Ba2+/Sr2+/Ca2+/DPMG molar ratio in the solution resulted in a surface layer with a composition of about 1.3:1 of c ation/DPMG. In the case of Zn2+/DPMG mixture the surface layer was composed of a mixture of slightly soluble Zn2+/DPMG (similar to3:1) and zinc hydrox ide. (C) 2001 Elsevier Science Ltd. All rights reserved.