Isao Sekine

Corrosion inhibition of mild steel by schiff base compounds in various aqueous solutions: part 1

Abstract The corrosion inhibition by Schiff base compounds derived from diamines and o -hydroxy, o -methoxy aromatic aldehydes was investigated by weight loss, electrochemical measurements and surface analysis of SS 400 in various aqueous solutions such as tap water (LC), concentrated tap water (HC) and HCl solutions. The maximum inhibition efficiency ( η ) of N,N′-bis (salicylaldehyde)-1,12-diaminododecane (Saldn) for SS 400 in HCl solution approached 93%. The adsorption of Saldn on mild steel in HCl solution was obeyed Langmuirs isotherm.

Oxygen Reduction Characteristics of Heat‐Treated Catalysts Based on Cobalt‐Porphyrin Ion Complexes

Oxygen reduction characteristics of graphite electrodes modified with aggregated cobalt-porphyrins heat-treated at various temperatures and then impregnated in Nafion polymer were investigated systematically. The aggregated cobalt-porphyrin compound was adsorbed on graphite powder and then heat-treated at various temperatures ranging from 200 through 1200 °C. The catalysts were evaluated for electroreduction performances of oxygen on modified electrodes in sulfuric acid solutions. The electrocatalytic performances of catalysts as measured in rotating ring-disk electrodes showed that the most effective catalytic activity for oxygen reduction was attained for the aggregated cobalt-porphyrin compounds on graphite powder heat-treated at temperatures between 600 and 800 °C. The surface concentration of Co and N as measured by X-ray photoelectron spectroscopy increased as the heat-treatment temperature was increased up to 800 °C. The electrochemical performance of pyrolyzed cobalt-porphyrin catalysts changed in parallel with the surface concentration of Co and N. In the temperature range 600-800 °C, it appeared that the increased catalytic activity originated from the well-dispersed Co-N 4 moiety or from fragments of the original molecules still retaining the cobalt bound to nitrogen atoms. In the higher temperature region, Co-N 4 bonds were no longer detected, and the presence of cobalt in the metallic states (β-Co) in the catalysts was confirmed by X-ray diffraction analysis. From the results of the stability tests, the pyrolyzed cobalt porphyrin electrode systems were found to be more stable than the nonheat-treated catalysts.

Syntheses of Polymerized Films on Mild Steels by Electro‐oxidation and Electroreduction and Their Corrosion Resistance

Polymer films, based on aniline‐, phenol‐, normal vinyl‐ and heterocyclic/vinyl‐type monomers, were synthesized on mild steel by various electropolymerizations (EPs), and their corrosion resistance and structure were investigated because a new coating system with corrosion resistance for mild steel has been obtained. The relationship between synthetic method, structure, and function (corrosion resistance) for coated mild steel is discussed. In electro‐oxidation polymerization (EOP) incomplete, porous, and thin films were formed on steel surfaces, while in electroreduction polymerization (ERP), complete, more compact, and thicker films were formed on steel surfaces in comparison with EOP films. The most corrosion‐preventive film under this experimental condition was a poly(2‐vinylpyridine) film with an inhibition efficiency (η) of corrosion of about 80–90%. The most effective EP method was a constant potential electrolysis using a two‐electrode cell with an η value of more than 90%. Since the organic layer formed during EP was ionic and the EP of 2‐vinylpyridine (monomer) was promoted, the thick poly(2‐vinylpyridine) film was formed on the steel surface. The results of structural analysis suggest that, (i) poly(2‐vinylpyridine) film, , was formed on the steel surface by EP, (ii) the coated steel was composed of polymer and steel layers, and oxidation products were not present in the interface, and (iii) the solvents in the film were evaporated and the thermal‐polymerization of poly(2‐vinylpyridine) continued with curing.

Corrosion Inhibition of Mild Steel by Cationic and Anionic Polymers in Cooling Water System

The behavior of corrosion inhibition of mild steel by various cationic and anionic polymers, that is, polyethyleneimine (PEI), its derivative (PEID), polyarylamine (PAAm) and polydicyanodiamide derivative (PDCDA) as cationic polymers and polymaleic acid derivative (PMAD), polyacrylic acid derivative (PAAD) and polyacrylic acid (PAA) as anionic polymers, was investigated by corrosion tests and physicochemical measurements. Testing was done in two pseudoconcentrated solutions with low (LC) and high (HC) concentrations of ionic species like Ca 2+ and Cl -

The corrosion inhibition of mild steel by ascorbic and folic acids

The effect of corrosion inhibition of several kinds of vitamins was investigated by measuring the corrosion weight loss of mild steel in 0.3% NaCl solution at 30°C. According to these results, the vitamins C (l-ascorbic acid; AA) and M (folic acid; FA) showed a good inhibition effect. The corrosion inhibition mechanism was investigated by measuring the weight loss, the polarization curves, and by IR and UV absorption spectroscopy. In 0.3% NaCl solution, the concentration of the AA showing a maximum corrosion inhibition was 200 ppm in the range 30–80°C, and that of the FA was 500 ppm at 30–40°C, and 100 ppm at 60–80°C. The mechanism of corrosion inhibition was considered to be due to chemical adsorption since AA and FA on the steel obeyed the Langmuir adsorption isotherm. The inhibition effect of AA and FA was decreased at higher concentration. because Fee2+ ions formed a chelatc compound and accelerated the corrosion of steel. When AA or FA was added to 0.03% NaCl solution at 30°C, and the test solution adjusted to pH value around neutrality, it was found that excellent inhibition occurred.

Recent evaluation of corrosion protective paint films by electrochemical methods

The deterioration of coating films has recently been evaluated by electrochemical methods, such as the alternating current (AC) impedance or electrochemical impedance spectroscopy (EIS) method, the current interrupter (CI) method, and the scanning vibrating electrode technique (SVET). Studies on the evaluation of coating films by the AC impedance method are found, especially in papers published from 1990 to 1995. The characteristics of the various electrochemical measurement methods, and a correlation between each electrochemical parameter value and visual observation rating are reviewed. There is a significant correlation between the evaluation by electrochemical measurement and that by visual observation. Guidelines and recent monitoring instruments for an evaluation method are also reviewed.

Oxygen reduction characteristics of graphite electrodes modified with cobalt di-quinolyldiamine derivatives

Abstract N , N ′-di-8-Quinolyltrimethylenediamine cobalt [Co(dqpr)] and N , N′ -di-8-quinolylphenylenediamine cobalt [Co(dqph)] were synthesized and tested as catalysts for electro-reduction of oxygen when immobilized on graphite electrodes. For modification on graphite, the complexes were mixed with graphite powder and heat-treated in Ar atmosphere at 400–800°C, then immobilized on graphite electrode with Nafion solution. The performance was improved significantly by the heat treatment, and it was assumed to be due to the formation of stabilized CoN 4 chelate structure still remaining on the graphite surface after pyrolysis. The polarization measurements revealed that the performance of the electrodes modified with the complexes was parallel to that of 5% platinum dispersed on carbon. Durability tests of the heat-treated complex at 80°C in acidic aqueous solutions showed relatively good catalytic performances as oxygen reduction catalysts, as compared with platinum. The potential usage of the complexes was demonstrated as the cathode catalysts in polymer electrolyte fuel cells in combination with fewer amounts of platinum, where a remarkable concerted effect is observed between platinum sites and CoN 4 centers dispersed on carbon substrate.

Electrochemical properties of metalloporphyrin-clay complex-modified electrode systems : investigation as oxygen sensors

Various electrodes modified with cobalt-porphyrin-clay complexes (CoTMPyP- and CoTAPP-Mon, Ver, and AW-Kao), silver colloid (AgCol), and polymers [PVA and P(2VPy)] were synthesized and their electrochemical properties were investigated to evaluate the possibility of creating oxygen sensors. The oxygen reduction based on the two-electron transfer mechanism (Eq. 1) occurred in the cobalt-porphyrin-clay/AgCol/polymer-modified electrode and the peak current density (I P ) depended quantitatively on the concentration of oxygen. As for the evaluation of oxygen sensors in the modified electrode systems at the optimal composition, (i) the I p increased linearly with the concentration of oxygen, (ii) the response was a reversible and rapid one, and (iii) the modified electrodes in the Mon and Ver systems were most stable (lifetime > 6 h under hydrodynamic conditions). The cobalt-porphyrin-clay/AgCol/polymer-modified electrode systems acted effectively as oxygen sensors

Corrosion Behavior of AISI 316 Stainless Steel in Formic and Acetic Acid Solutions

Abstract The corrosion behavior of AISI 316 stainless steel (SS) in formic and acetic acids was investigated by measuring the corrosion weight loss, the polarization curve, the impedance at the steel/solution interface, and the variation of natural electrode potential (NEP) with time. It was found that the corrosion rate of AISI 316 SS in formic and acetic acids was markedly dependent on the concentration of the acid and temperature. The corrosion rate in aqueous solution of these acids was larger than in nonaqueous solution, and the corrosion behavior in nonaqueous solution was quite different from that in aqueous solution. It was believed that Cr and Mo mainly contribute to the corrosion resistance of AISI 316 SS in aqueous solution, while Ni contributes slightly. In nonaqueous solution of formic acid, Cr mainly contributes to corrosion resistance, and Mo and Fe contribute slightly; in nonaqueous solution of acetic acid, Cr mainly contributes to corrosion resistance, while Mo contributes slightly. To ob...

Corrosion behaviour of type 430 stainless steel in formic and acetic acids

Abstract The corrosion behaviour of Type 430 stainless steel in formic and acetic acid solutions was investigated by measuring the corrosion weight loss, the polarization curve, the corrosion potential variation with time and the impedance at the steel-solution interface. The corrosion rate of the steel in formic and acetic acid solutions was markedly dependent on the concentration of acid and the temperature. In acetic acid at boiling point, particularly, the corrosion rate in non-aqueous solution was considerably increased as the amounts of water decreased below 5%. It went up to about 4000 mdd, when the content of water was 65 ppm. By using ion micro-analysis (IMA), chromium was observed to be extraordinarily enriched on the surface layer of the steel.