Erika Kálmán

Corrosion Inhibitors—Correlation between Electronic Structure and Efficiency

Abstract Corrosion inhibition efficiencies of heterocyclic, unsaturated (aromatic and nonaromatic) compounds (pyrimidines, benzothiazole derivatives, amino acids containing an aromatic part, pyridi...

Nonlinear group-contribution models of corrosion inhibition

Abstract The correlation between the molecular structure and inhibitor efficiency (Ei) of triamines was investigated. The group-contribution approach was adapted to account for Langmuir- and Frumki...

LKP model of the inhibition mechanism of thiourea compounds

Abstract Interaction of corrosion inhibitors with metal surfaces in acidic solutions was investigated using a nonlinear model encompassing the Langmuir adsorption isotherm. A regression equation, w...

Polynomial model of the inhibition mechanism of thiourea derivatives

Interaction of corrosion inhibitors with metal surfaces in acidic solutions was modelled by using a polynomial model based on the Langmuir adsorption isotherm. The curve-fitting procedure yielded a regression equation with a multiple correlation coefficient equal to 0.982.

Corrosion inhibition by 1-hydroxy-ethane-1,1-diphosphonic acid : an electrochemical impedance spectroscopy study

Impedance spectra of carbon steel in the presence of 1-hydroxy-ethane-1,1-diphosphonic acid (HEDP) has been investigated in neutral solutions. The aim of the measurements was to study the effect of HEDP on the carbon steel corrosion as a function of inhibitor concentration. An optimal inhibitor concentration was found. A two-time constant equivalent circuit model including a constant phase element was consistent with experimental data in the frequency range studied. The system parameters, obtained by a nonlinear fit procedure are discussed in terms of the model used. Inhibitor efficiencies derived from impedance data are compared with those obtained from polarization and weight loss measurements. Results of these investigations show that a low concentrations, HEDP inhibits carbon steel corrosion by a precipitation mechanism forming insoluble iron complexes and repairing the porous oxide layer formed n the metal surface. Increasing HEDP concentration beyond the optimal value decreases its inhibition efficiency due to the dissolution of the oxide layer.

Effects of Bivalent Cations on Corrosion Inhibition of Steel by 1‐Hydroxyethane‐1,1‐diphosphonic Acid

The influence of calcium and zinc ions on the corrosion inhibition effect of 1-hydroxyethane-1,1-diphosphonic acid (HEDP) on carbon steel has been investigated by electrochemical techniques, X-ray photoelectron spectroscopy, and atomic force microscopy. Addition of calcium or zinc ions greatly increased the inhibition efficiency of HEDP in a synergistic manner. The highest inhibition effect was obtained for molar ratios of Ca/HEDP = 0.5 and Zn/HEDP = 3 for 3 X 10 -4 mol dm -3 HEDP. The corrosion inhibition mechanism in the presence of these additives proved to be different from that with HEDP alone and was related to the formation of different complex species between HEDP and cation additives. The frequency response of the studied system was described by a transfer function containing two relaxation time constants corresponding to the charge-transfer process and the porous oxide layer. Higher zinc and phosphorous content in the inhibitor layer and a continuous change in the O-Fe and HO-Fe ratio were achieved by increasing zinc concentration in the solution (in the range Zn/HEDP = 0.5-3) as supported by XPS measurements. Changes in the chemical structure were established in the oxide-hydroxide layer developed spontaneously on the steel surface. The synergistic effect of inhibitor compounds appeared also in surface morphology, leading to the development of smooth, i.e., dense, protective layers as revealed by atomic force microscopy.

Influence of cations on the corrosion inhibition efficiency of aminophosphonic acid

Abstract The iron/electrolyte interphase has been studied in the presence of N , N -di(phosphonomethyl)glycine (DPMG) inhibitor with or without the bivalent cations. In electrochemical measurements, inhibition was assumed by the formation of a complex in the presence of DPMG. In situ atomic force microscopy provided direct insight into changes in the surface morphology at several hundred nanometres when topographical changes owing to the breakdown of the passive layer, and initiation of corrosion were monitored. Section analysis has revealed the degree of deterioration. Bivalent cations (Ba 2+ , Sr 2+ , Ca 2+ and Zn 2+ ) synergically improved the activity of DPMG, though the mechanism was different. Barium, strontium and calcium ions in blends hindered the anodic iron dissolution, while zinc ions influenced both the anodic and cathodic processes. Composition of the surface layer was analysed by X-ray photoelectron spectroscopy (XPS). The 2:1 Ba 2+ /Sr 2+ /Ca 2+ /DPMG molar ratio in the solution resulted in a surface layer with a composition of about 1.3:1 of cation/DPMG. In the case of Zn 2+ /DPMG mixture the surface layer was composed of a mixture of slightly soluble Zn 2+ /DPMG (∼3:l) and zinc hydroxide.

An investigation of copper corrosion inhibition in chloride solutions by benzo-hydroxamic acids

Benzo-hydroxamic acids (BHA) are investigated as potential copper corrosion inhibitors in chloride solution. The BHAs investigated were: p-chloro-benzo-hydroxamic (p-Cl-BHA), o-chloro-benzo-hydroxamic acid (o-Cl-BHA), P-nitro-benzo-hydroxamic acid (p-N-BHA) and o-methyl-benzo-hydroxamic acid (o-M-BHA). Electrochemical measurements, potentiostatic polarization and ac impedance spectroscopy were carried out to evaluate the inhibition effect of the investigated BHAs. An Electrochemical Quartz Crystal Microbalance (ECQM) was used to measure electrode corrosion and inhibitor adsorption or layer formation processes. A poorly soluble layer consisting of the inhibitor and copper corrosion products is proposed to account for the protective effect in chloride solutions.

New inhibitors for copper corrosion

The study of the effectiveness of several potential copper corrosion inhibitors in acidic media was studied. The investigated thiazole derivative functional groups contain heterocyclic atoms such as nitrogen, sulfur, and oxygen. Thiazole derivatives, 5-benzylidene-2,4-dioxotetrahydro-1,3-thiazole (BDT) 5-(4¢-isopropylbenzylidene)-2,4-dioxotetrahydro-1,3-thiazole (IPBDT), 5-(3¢-thenylidene)-2,4-dioxotetrahydro-1,3-thiazole (TDT), and 5-(3¢,4¢-dimetoxybenzylidene)-2,4-dioxotetrahydro-1,3-thiazole (MBDT) were tested for copper corrosion inhibition properties. The electrolyte solution was 0.1 M Na2SO4. In situ information on corrosion and inhibition processes can be obtained using different techniques. Electrochemical measurements (EIS), in situ scanning probe microscopy (SPM), in addition to quartz crystal microbalance (QCM) measurements were applied. Those methods are very useful owing to their high sensitivity and resolution. Dynamic STM and AFM measurements on Cu(111) single-crystal electrode with and without the addition of some inhibitors were performed. The presence of the isopropyl group in the case of IPBDT produced far better protection against copper corrosion in acidic sulfate-containing media than the rest of the derivatives.

The role of oxide layer formation during corrosion inhibition of mild steel in neutral aqueous media

Abstract The influence of phosphonic acid with Ca cation on iron surfaces in neutral aerated media (0.5 mol dm − NaClO 4 ) has been studied by electrochemical and surface analytical methods. X-ray induced photoelectron (XPS) and Auger electron spectroscopy (XAES) provided the possibility for identification of different chemical states of the constituents of the corrosion protective layers. The presence of certain cations led to a synergistic effect. It was found that calcium ions were incorporated into the film that developed on the mild steel surface, containing a mixed oxide and hydroxide complex. Electrochemical Impedance Spectroscopy (EIS) was used to determine the inhibitor efficiency of phosphonic acid at different concentrations. The data obtained were fitted and modelled by an equivalent circuit model.