PASSIVE FILMS AND CORROSION PROTECTION DUE TO PHOSPHONIC ACID INHIBITORS

For protecting mild steel from corrosion, amino-trimethylidenephosphonic acid (ATMP) was more effective than 1-hydroxyethylidene diphosphonic acid (HEDP), N.N-dimethylidenephosphonoglycine (DMPG), 1-ethyl-phosphonoethylidenediphosphonic acid (EEDP), and ethylenediaminetetramethylidenephosphonic acid (EDTMP). A 20-min treatment in 1.0 mol/L of ATMP with a pH 0.23 at 45-degrees-C formed an anti-corrosive complex film that was composed of 48.4% O,28.6% P, 7.0% Fe, 4.3% N, and 11.7% C, based on x-ray photoelectron spectroscopy and Auger electron spectroscopy From differences in binding energies of Fe, N, and O, in the shift of C-N and P-O vibration, in the reflection FTIR spectra, and in the change of P-OH and Fe-N vibration before and after film formation, it was deduced that N and O in ATMP were coordinated with Fe2+ in the film.