Takao Murakawa

Coverage of iron surface by organic compounds and anions in acid solutions

Abstract The electrical double layer capacities at the interface between iron and acid solutions containing organic inhibitors and halide ions were measured as a function of inhibitor concentrations. The degree of surface coverage as calculated from the change in capacity due to adsorption of inhibitors was compared to inhibitor efficiency. These showed a linear relationship which might be used as a means for evaluation of inhibitors. Peaks in coverage-concentration or inhibitor-efficiency-concentration curves are interpreted in terms of a change of mechanism from adsorption to film-forming inhibition. Synergism of amines and halide ions is discussed from a viewpoint of surface charge. A model of co-adsorption using halide ions and organic cations suitably interprets the phenomenon.

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

Ellipsometric Determination of Greasy Layer on Aluminum

The greasy layer remaining on aluminum as rolled is usually vaporized during annealing process; and contact angle is most commonly measured to check if the surface is free from the organic contaminations. In this paper, the possibility and limitations of applying ellipsometry for such a measurement were examined in the hope that the thickness of the greasy film might be determined more quantatively. Because of an complicated calculation of two-layer system consisting of both aluminum oxide film and the grease layer, an approximate method was used. The validity of this approximation was ascertained by measuring the built-up film of stearic acid on electropolished aluminum, the thickness of which had been previously known. The variation in the greasy layer thickness, thus measured with the specimens heated at variety of temperatures, indicates that the remaining oil on aluminum is almost completely depleted at temperatures higher than 400°C and then oxidation of aluminum takes palce instead.

Determination of Cleanliness of Metal Surfaces by Measurement of Coefficient of Friction

An apparatus was prepared for trial for measuring the frictional force between a ball slider and a plane specimen by means of a strain gauge. By using this apparatus, the authors measured the decrease in coefficient of friction (μκ) of clean metal surfaces, which had resulted from their contamination with polar and non-polar organic compounds. At a very early stage of contamination, stick-slip waves appeared in oscillating curves of frictional force scanned with the slider from one to the other end of the specimen; but, smooth curves were finally obtained when the surface was covered with monolayers of organic compounds with the proceeding of contamination. Oleic acid, which had been adsorbed on metal surfaces by vapor condensation, retraction, or Langmuir-Blodgetts Technique, reduced μκ of metals in decreasing order of Cu>Fe>Al and stainless steels, which would be explained in terms of the differences in chemisorption. Octadecane also reduced μκ; but it had a marked distinction that μκ depended on the load of slider. From these points of view, it was proposed that the measuring of the coefficient of friction by using the above apparatus can be applied to determine the cleanliness of metal surfaces.

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.