Norman Hackerman

Investigation of the inhibitive effect of ortho-substituted anilines on corrosion of iron in 1 M HCl solutions

The inhibitory activity of some o-substituted anilines on iron corrosion in hydrochloric acid (HCl) was studied in relation to inhibitor concentration using potentiodynamic and electrochemical impedance spectroscopy (EIS) measurements. O-substituted anilines were found to act as mixed type inhibitors. The results showed that o-substituted anilines suppressed both cathodic and anodic processes of iron corrosion in 1 M HCl by its adsorption on the iron surface according to Langmuir adsorption isotherm. Potentiodynamic and EIS measurements reveal that these compounds inhibit the iron corrosion in 1 M HCl and that the efficiency increases with increasing of the inhibitor concentration. Data obtained from EIS are analyzed to model the corrosion inhibition process through equivalent circuit.

Corrosion Inhibition in HCl Using Methyl Pyridines

The inhibiting effect of pyridine and seven of its methyl derivatives on the corrosion of iron in O2‐free, at 35°C was determined. Corrosion rates were measured by colorimetric analysis for iron with mercaptoacetic acid. The relative inhibitor efficiency and cathodic potential shift increased with increasing inhibitor concentration and, for a given concentration, with increasing electron density at the nitrogen atom. Both increased slightly with decreasing concentration, but a temperature increase of 10°C had no effect on either. The proposition that chemisorption is involved in corrosion inhibition is supported by these experiments. As a supplementary item the great importance of careful purification of the organic compounds used in such researches as this is documented.

Corrosion Inhibition by Organic Amines

The corrosion of pure iron in 1N HC1 is discussed in terms of the theory of mxed potentials and the theory is applied to inhibition by organic compounds. Corrosion rates with and without inhibition by aniline, several aniline derivatives, and alkylamines were determned by cathodic polarization measurements as well as by colorimetric analysis of the solution. It is shown that all compounds show a maximum inhibitor efficiency at a concentration of approxdmately 0.1 mole/1, that with one exception all are cathodic as well as anodic inhibitors, and that in most cases they are predominantly anodic inhibitors. An interpretation of the data on cathodic inhibition is suggested on the basis of the assumption of a uniform metal surface and uniform adsorption. The interpretation of anodic inhibition is found to be difficult due to a lack of satisfactory experimental data. (auth)

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.

Kinetics of Iron Corrosion in Concentrated Acidic Chloride Solutions

The kinetics of active iron dissolution at 25°C has been studied in deaerated 1N and 6N chloride solutions for hydrogen ion concentrations of 0.1–6.0N. For 1N chloride solutions with , the dissolution reaction is described by anodic Tafel slope and electrochemical reaction order with respect to hydrogen ion activity . These parameters are characteristic of a dissolution mechanism in which chemisorbed halide ions interact with adsorbed hydroxyl ions in a two‐electron rate‐determining step. For 6N chloride solutions, this mechanism holds only over a narrower (H+) region up to 0.24N, in which . With increased ; and for , indicating that the hydrogen ion (and no longer the hydroxyl ion) catalyzed the dissolution reaction. A positive value of ensues for synergistic adsorption of hydrogen ions on the halide ion covered surface. A formal detailed dissolution mechanism is proposed, giving and , in agreement with experiment. Alternate dissolution mechanisms including one‐electron transfer schemes are discussed.

Anodic passivation of tin in slightly alkaline solutions

Abstract The anodic oxidation of tin in 0.2 M borate buffer solution has been studied by potentiodynamic, potentiostatic and galvanostatic techniques. It was found that although a large amount of charge is consumed during anodic oxidation, only a fraction of this charge is involved in film growth. The initial stages of metal passivation under dynamic conditions are best described by Muellers dissolution—precipitation model. Under potentiostatic conditions two different equations describe the kinetics of film formation. For anodic potentials lower than 1.6 V vs sce a logarithmic dependence holds between cathodic charge and time. At higher potentials, the growth rate is controlled by a nucleation process and the rate law is more complicated. Under galvanostatic conditions the logarithms of the growing time is proportional to the inverse of the cathodic charge. These results are discussed in terms of theories of film growth.

Carbon Dioxide Reduction at a Metal Phthalocyanine Catalyzed Carbon Electrode

Metal phthalocyanines (metal = Co, Ni) deposited on carbon electrodes have been found to catalyze the electroreduction of carbon dioxide to formic acid in acid solutions (pH = 3-7). The overpotential for CO/sub 2/ reduction on cobalt phthalocyanine is approximately 200 mV lower than on the best metal cathodes at currents up to 10 mA/cm/sup 2/. The main reaction product in long-term electrolysis is the formate ion at pH>5. Methanol is also produced at lower pH values. The phthalocyanine becomes inactive in the less acid solutions once a fairly negative potential is imposed, probably due to an irreversible reduction of the catalyst.

A photo-electrochemical investigation of semiconducting oxide films on copper

Abstract p -type copper oxides formed by electrochemical and chemical methods are compared using voltammetry and photo-electrochemical techniques. Cupric and cuprous films exhibit characteristic photo-current signals, the sign and magnitude of which are a function of band curvature. Semi-conductor properties and aspects of the band structure of the surface films have been determined from observations of the spectral dependence of photo-assisted charge transfer. The positions of voltammetry peaks and the standard potentials of oxide formation are correlated with the flat band potentials of Cu 2 O and CuO. The inhibition of copper oxidation by illumination and the corrosion of copper in solutions containing O 2 are discussed with regard to derived semiconductor models.

Adsorption of Monomeric and Polymeric Amino Corrosion Inhibitors on Steel

The adsorption of 4-ethylpyridine, 4-ethylpiperidine, and very low molecular weight poly (4-vinylpyridines) was studied in cyclohexane solutions containing hydrogen reduced steel powder. Isotherms were obtained for the monomers at 30

Iron Oxide Semiconductor Electrodes in Photoassisted Electrolysis of Water

C. They show that an amount equivalent to monolayer formation is absorbed at equilibrium concentrations in the range 2.5 to 5.0 x 10U-3DM. The polymer was adsorbed to a much greater extent. Using a specially designed chromatographic method, the heat of adsorption of the piperidine derivative from cyclohexane was determined. Simultaneous measurements of the adsorption of the polymer and the corrosion of the steel in aqueous hydrochloric acid have shown that the corrosion rate decreases by 80% as the polymer adsorbs to form a very incomplete layer. From these results, it is concluded that these compounds chemisorb to the steel surface and that the 4-ethylpiperidine is bonded at the nitrogen atom, but that the 4-ethlpyridine is adsorbed in a position with the plane of the ring parallel to the steel surface. (13 refs.)