Toshiharu Kato

A contribution to the understanding of the synergistic effect of anions for the corrosion inhibition of Fe by amines

Synergistic and antagonistic effects of organic or inorganic anions with alkyl or cyclic amines were observed in the corrosion inhibition of Fe in HClO4. Anions specifically adsorbed on Fe attract amine cations electrostatically into the Helmholtz electrical double layer. If the electron availability of the amines is insufficient, the cationic amines simply cover the anion layer rather than chemisorb directly on the Fe surface. In the case of weak anion adsorption, however, the cations often tend to withdraw the adsorbed anions into the HClO4. Synergistic adsorption is, therefore, classified into two types plus a mixture of the two : (1) specific co-adsorption of anions and amines, as reported in a previous paper5; and (2) ionic or physical overlap adsorption of amine cations over the anion-covered Fe surface. In the latter case, increase of amine concentration may cause withdrawal of the anions from the Fe surface into the solution. The surface coverage thus decreases and, as a result, an antagonistic effect should be observed.

Differential capacity curves of iron in perchloric acid in the presence of anions

Abstract Influences of inorganic anions on the differential capacity ( C ) vs. electrode potential ( E ) curves of iron in perchloric acid solution system have been measured by the single pulse method. Three capacity maxima for HClO 4 alone are interpreted as being due to: (1) OH −1 desorption or, alternatively, reorientation of water dipole molecules; (2) adsorption of ClO 4 poststaggered− ; and (3) adsorption of hydrogen evolution precursors. Heights of the capacity maxima and potentials at which they take place depend greatly on the perchloric acid concentration. Addition of Cl − , Br − , or SO 4 poststaggered− to the HClO 4 solution shifted the peaks and suppressed the curve over the entire potential region. Furthermore, new peaks attributable to the adsorption or desorption of added ions were observed. With l − the peaks were lacking and the curves were depressed, implying less reversible sorption of iodide ion than for the other halide ions. Adsorb ability of inorganic anions examined in these experiments was in the order: F − 4 poststaggered− 2 − − − .

Differential capacity vs. electrode potentialcurves for Fe-HClO4 in the presence of organic anions

Abstract The influence of acetate, propionate and citrate anions on the differential capacity vs.electrode potential curves of the Fe-HClO 4 system was examined. Each of these organic anions introduced a new adsorption-desorption peak, while both the water-reorientation peak and the ClO 4 − desorption peak were suppressed by the addition of the organic acids. The potential of the H-adsorption peak was shifted to more anodic values as a result of the adsorption of the negatively charged organic anions, but this peak was eventually suppressed as the concentration of the additives increased. Addition of ClO 4 − to the Fe-HClO 4 system containing acetate or propionate anions produced a broad peak. This is interpreted in terms of the co-adsorption of ClO 4 − and the organic anions. Such a peak was not appreciable in the case of citrate. The order of the degree of adsorbability of the organic anions, estimated from the extent of the suppression of C-E curves, was acetate

Synergistic Action of Organic Anions and Amines for Corrosion Inhibition of Iron in Perchloric Acid Solutions

Increase of the covering power of the surface of iron in perchloric acid solution caused by the synergistic action of organic anions and amines was measured by electrical double layer capacity at the interface. The covering power increased by the addition of amine into Fe-0.5N-HClO4 system containing sodium propionate, but it decreased by the addition of a larger amount of amine. These findings should be interpreted as adsorption of amines as ammonium ions over the previously adsorbed propionate ions; however, as the results of electrostatic interaction between anions and cations, anions would migrate from the iron surface together with ammonium cations with the increase of amine concentration.Accordingly, the synergistic effects of amines and anions would be attributed to the overlapped adsorption of ammonium ions over the anions, and these effects should be quite distinct from the coadsorption mechanism of amine and halide ions.