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2 pages, 152 KiB

Open AccessEditorial

Corrosion Inhibition

by Robert Lindsay and Anton Kokalj

Metals 2018, 8(10), 821; https://doi.org/10.3390/met8100821 - 12 Oct 2018

Cited by 4 | Viewed by 2259

Abstract

n/a Full article

(This article belongs to the Special Issue Corrosion Inhibition)

Research

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28 pages, 8658 KiB

Open AccessFeature PaperArticle

DFT Study of Azole Corrosion Inhibitors on Cu₂O Model of Oxidized Copper Surfaces: II. Lateral Interactions and Thermodynamic Stability

by Dunja Gustinčič and Anton Kokalj

Metals 2018, 8(5), 311; https://doi.org/10.3390/met8050311 - 1 May 2018

Cited by 16 | Viewed by 4760

Abstract

The adsorption of imidazole, triazole, and tetrazole—used as simple models of azole corrosion inhibitors—on various Cu

_{2}

O(111)- and Cu

_{2}

O(110)-type surfaces was characterized using density functional theory (DFT) calculations with the focus on lateral intermolecular interactions and the thermodynamic stability of [...] Read more.

The adsorption of imidazole, triazole, and tetrazole—used as simple models of azole corrosion inhibitors—on various Cu

_{2}

O(111)- and Cu

_{2}

O(110)-type surfaces was characterized using density functional theory (DFT) calculations with the focus on lateral intermolecular interactions and the thermodynamic stability of various adsorption structures. To this end, an ab initio thermodynamics approach was used to construct two-dimensional phase diagrams for all three molecules. The impact of van der Waals dispersion interactions on molecular adsorption bonding was also addressed. Lateral intermolecular interactions were found to be the most repulsive for imidazole and the least for tetrazole, for which they are usually even slightly attractive. Both non-dissociative and dissociative adsorption modes were considered and although dissociated molecules bind to surfaces more strongly, none of the considered structures that involve dissociated molecules appear on the phase diagrams. Our results show that the three azole molecules display a strong tendency to preferentially adsorb at reactive coordinatively unsaturated (CUS) Cu surface sites and stabilize them. According to the calculated phase diagrams for Cu

_{2}

O(111)-type surfaces, the three azole molecules adsorb to specific CUS sites, designated as Cu

^{CUS}

, under all conditions at which molecular adsorption is stable. This tentatively suggests that their corrosion inhibition capability may stem, at least in part, from their ability to passivate reactive surface sites. We further comment on a specific drawback due to neglect of configurational entropy that is usually utilized within the ab initio thermodynamics approach. We analyze the issue for Langmuir and Frumkin adsorption models and show that when configurational entropy is neglected, the ab initio thermodynamics approach is too hasty to predict phase-transition like behavior. Full article

(This article belongs to the Special Issue Corrosion Inhibition)

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27 pages, 29354 KiB

Open AccessArticle

DFT Study of Azole Corrosion Inhibitors on Cu₂O Model of Oxidized Copper Surfaces: I. Molecule–Surface and Cl–Surface Bonding

by Dunja Gustinčič and Anton Kokalj

Metals 2018, 8(5), 310; https://doi.org/10.3390/met8050310 - 1 May 2018

Cited by 34 | Viewed by 6672

Abstract

The adsorption of three simple azole molecules—imidazole, triazole, and tetrazole—and Cl on various sites of several Cu

_{2}

O(111)- and Cu

_{2}

O(110)-type surfaces, including Cu and O vacancies, was characterized using density functional theory (DFT) calculations; the three molecules can be seen [...] Read more.

The adsorption of three simple azole molecules—imidazole, triazole, and tetrazole—and Cl on various sites of several Cu

_{2}

O(111)- and Cu

_{2}

O(110)-type surfaces, including Cu and O vacancies, was characterized using density functional theory (DFT) calculations; the three molecules can be seen as models of azole corrosion inhibitors and Cl as a corrosion activator. Both non-dissociative and dissociative adsorption modes were considered for azole molecules; the latter involves the N–H bond cleavage, hence we also addressed the adsorption of H, which is a co-product of the dissociative adsorption. We find that molecules and Cl bind much stronger to unsaturated Cu sites compared to saturated ones. Dissociated molecules bind considerably stronger to the surface compared to the intact molecules, although even the latter can bind rather strongly to specific unsaturated Cu sites. Bader analysis reveals that binding energies of dissociated molecules at various Cu sites correlate with Bader charges of Cu ions before molecular adsorption, i.e., the smaller the Cu charge, the stronger the molecular bonding. All three azole molecules display similar non-dissociative adsorption energies, but significant difference between them appears for dissociative adsorption mode, i.e., dissociated triazole and tetrazole bind much stronger than dissociated imidazole because the former two can form two strong N–Cu bonds, but imidazole cannot due to its incompatible molecular geometry. Dissociative adsorption is consequently favorable only for triazole and tetrazole, but only at oxygen vacancy sites, where it proceeds barrierlessly (or almost so). This observation may suggest that, for imidazole, only the neutral form, but, for triazole and tetrazole, also their deprotonated forms are the active species for inhibiting corrosion under near neutral pH conditions, where copper surfaces are expected to be oxidized. As for the comparison with the Cl–surface bonding, the calculations indicate that only dissociated triazole and tetrazole bind strong enough to rival the Cl–surface bonds. Full article

(This article belongs to the Special Issue Corrosion Inhibition)

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20 pages, 1705 KiB

Open AccessArticle

The Effect of Cerium Ions on the Structure, Porosity and Electrochemical Properties of Si/Zr-Based Hybrid Sol-Gel Coatings Deposited on Aluminum

by Peter Rodič, Jozefina Katić, Dorota Korte, Paula M. Desimone, Mladen Franko, Silvia M. Ceré, Mirjana Metikoš-Huković and Ingrid Milošev

Metals 2018, 8(4), 248; https://doi.org/10.3390/met8040248 - 7 Apr 2018

Cited by 22 | Viewed by 5559

Abstract

This study was focused on the synthesis and characterization of Si/Zr-based hybrid sol-gel coatings with and without the addition of cerium(III) ions. The coatings were deposited on aluminum aiming to act as an effective and ecologically harmless alternative to toxic chromate coatings. The [...] Read more.

This study was focused on the synthesis and characterization of Si/Zr-based hybrid sol-gel coatings with and without the addition of cerium(III) ions. The coatings were deposited on aluminum aiming to act as an effective and ecologically harmless alternative to toxic chromate coatings. The chemical composition, structure, thermal properties and porosity of the non-doped and Ce-doped coatings containing various Zr contents were examined by Raman spectroscopy and photothermal beam deflection spectroscopy. The corrosion properties of the coated aluminum substrates were studied using AC and DC electrochemical methods in 0.1 M NaCl electrolyte solution. Barrier and protecting properties of the coatings were monitored upon long-term immersion in chloride solution using electrochemical impedance spectroscopy. The effect of cerium ions was two-fold: on the formation of a more condensed Si−O−Zr network structure and on the formation of Ce-based deposits, which diminish the rate of cathodic reaction at the coating/metal interface. These effects acted synergistically and resulted in the creation of the coatings with effective barrier and active corrosion protection. Full article

(This article belongs to the Special Issue Corrosion Inhibition)

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15 pages, 878 KiB

Open AccessFeature PaperArticle

Interaction of Model Inhibitor Compounds with Minimalist Cluster Representations of Hydroxyl Terminated Metal Oxide Surfaces

by Christopher D. Taylor, Yathish Kurapati and Sujit K. Mondal

Metals 2018, 8(2), 81; https://doi.org/10.3390/met8020081 - 23 Jan 2018

Cited by 4 | Viewed by 3780

Abstract

The computational modeling of corrosion inhibitors at the level of molecular interactions has been pursued for decades, and recent developments are allowing increasingly realistic models to be developed for inhibitor–inhibitor, inhibitor–solvent and inhibitor–metal interactions. At the same time, there remains a need for [...] Read more.

The computational modeling of corrosion inhibitors at the level of molecular interactions has been pursued for decades, and recent developments are allowing increasingly realistic models to be developed for inhibitor–inhibitor, inhibitor–solvent and inhibitor–metal interactions. At the same time, there remains a need for simplistic models to be used for the purpose of screening molecules for proposed inhibitor performance. Herein, we apply a reductionist model for metal surfaces consisting of a metal cation with hydroxide ligands and use quantum chemical modeling to approximate the free energy of adsorption for several imidazoline class candidate corrosion inhibitors. The approximation is made using the binding energy and the partition coefficient. As in some previous work, we consider different methods for incorporating solvent and reference systems for the partition coefficient. We compare the findings from this short study with some previous theoretical work on similar systems. The binding energies for the inhibitors to the metal hydroxide clusters are found to be intermediate to the binding energies calculated in other work for bare metal vs. metal oxide surfaces. The method is applied to copper, iron, aluminum and nickel metal systems. Full article

(This article belongs to the Special Issue Corrosion Inhibition)

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3257 KiB

Open AccessFeature PaperArticle

Inhibition of Brass (80/20) by 5-Mercaptopentyl-3-Amino-1,2,4-Triazole in Neutral Solutions

by Ivan А. Arkhipushkin, Khidmet S. Shikhaliev, Andrei Y. Potapov, Lyudmila V. Sapronova and Leonid P. Kazansky

Metals 2017, 7(11), 488; https://doi.org/10.3390/met7110488 - 9 Nov 2017

Cited by 18 | Viewed by 7320

Abstract

The effect of the adsorption of 5-mercaptopentyl-3-amino-1,2,4-triazole (MPATA) on the corrosive behavior of brass (Cu80/Zn20) in neutral (pH 7.4) borate buffer solutions with and without 0.01 M NaCl was studied. Electrochemical methods show significant decrease of the anodic and cathodic currents on the [...] Read more.

The effect of the adsorption of 5-mercaptopentyl-3-amino-1,2,4-triazole (MPATA) on the corrosive behavior of brass (Cu80/Zn20) in neutral (pH 7.4) borate buffer solutions with and without 0.01 M NaCl was studied. Electrochemical methods show significant decrease of the anodic and cathodic currents on the polarization curves in the presence of MPATA. X-ray photoelectron spectroscopy (XPS) reveals MPATA adsorption on the brass surface from an inhibitor solution. After 17 h of exposure, a mixed complex [Cu_xZn_yMPATA_z] with a thickness of about 3–3.5 nm is formed on the surface. This nanolayer has sufficient protective ability to withstand corrosion tests in a salt fog chamber: after 5 days of testing, the samples remain glossy and less than 1% of the surface has been damaged. After corrosion tests in a salt fog chamber, the surface of unprotected samples is enriched with zinc, while at the surface of inhibitor-treated samples, the copper and zinc are present in practically equal contents. Full article

(This article belongs to the Special Issue Corrosion Inhibition)

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2608 KiB

Open AccessFeature PaperArticle

DFT Modelling of Cu Segregation in Al-Cu Alloys Covered by an Ultrathin Oxide Film and Possible Links with Passivity

by Pauline Cornette, Dominique Costa and Philippe Marcus

Metals 2017, 7(9), 366; https://doi.org/10.3390/met7090366 - 12 Sep 2017

Cited by 10 | Viewed by 6040

Abstract

We modelled with Density Functional Theory (DFT) an Al-Cu alloy covered with a passive film, with several Cu concentrations (from the limit of the isolated atom to the monolayer) at the interface with the oxide, as well as Guinier-Preston 1 (GP1) zones. At [...] Read more.

We modelled with Density Functional Theory (DFT) an Al-Cu alloy covered with a passive film, with several Cu concentrations (from the limit of the isolated atom to the monolayer) at the interface with the oxide, as well as Guinier-Preston 1 (GP1) zones. At low (respectively high) concentration, Cu segregates in the first (respectively second) metal layer underneath the passive film. The Cu monolayer is the most stable configuration (−0.37 eV/Cu atom). GP1 zones were modelled, with a three-copper atom cluster in the alloy. The GP1 zone is slightly favoured with respect to the Cu monolayer under the oxide film. A low (respectively high) Cu concentration induces an electronic workfunction increase (respectively decrease) by 0.3 eV (respectively −0.4 to −0.6 eV) as compared to pure Al. In contrast, without oxide, Cu segregation at the Al surface induces no workfunction change at low concentration and an increase of 0.3 eV of the workfunction at high concentration. Thus, the presence of oxide modifies the expected tendency of workfunction increase by adding a more noble metal. For the studied models, no spontaneous electron transfer occurs to the O₂ molecule. Full article

(This article belongs to the Special Issue Corrosion Inhibition)

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Review

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695 KiB

Open AccessFeature PaperReview

Predicting the Performance of Organic Corrosion Inhibitors

by David A. Winkler

Metals 2017, 7(12), 553; https://doi.org/10.3390/met7120553 - 8 Dec 2017

Cited by 78 | Viewed by 7473

Abstract

The withdrawal of effective but toxic corrosion inhibitors has provided an impetus for the discovery of new, benign organic compounds to fill that role. Concurrently, developments in the high-throughput synthesis of organic compounds, the establishment of large libraries of available chemicals, accelerated corrosion [...] Read more.

The withdrawal of effective but toxic corrosion inhibitors has provided an impetus for the discovery of new, benign organic compounds to fill that role. Concurrently, developments in the high-throughput synthesis of organic compounds, the establishment of large libraries of available chemicals, accelerated corrosion inhibition testing technologies, and the increased capability of machine learning methods have made discovery of new corrosion inhibitors much faster and cheaper than it used to be. We summarize these technical developments in the corrosion inhibition field and describe how data-driven machine learning methods can generate models linking molecular properties to corrosion inhibition that can be used to predict the performance of materials not yet synthesized or tested. We briefly summarize the literature on quantitative structure–property relationships models of small organic molecule corrosion inhibitors. The success of these models provides a paradigm for rapid discovery of novel, effective corrosion inhibitors for a range of metals and alloys in diverse environments. Full article

(This article belongs to the Special Issue Corrosion Inhibition)

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2980 KiB

Open AccessFeature PaperReview

Neutron Reflectometry for Studying Corrosion and Corrosion Inhibition

by Mary H. Wood and Stuart M. Clarke

Metals 2017, 7(8), 304; https://doi.org/10.3390/met7080304 - 8 Aug 2017

Cited by 16 | Viewed by 9435

Abstract

Neutron reflectometry is an extremely powerful technique to monitor chemical and morphological changes at interfaces at the angstrom-level. Its ability to characterise metal, oxide and organic layers simultaneously or separately and in situ makes it an excellent tool for fundamental studies of corrosion [...] Read more.

Neutron reflectometry is an extremely powerful technique to monitor chemical and morphological changes at interfaces at the angstrom-level. Its ability to characterise metal, oxide and organic layers simultaneously or separately and in situ makes it an excellent tool for fundamental studies of corrosion and particularly adsorbed corrosion inhibitors. However, apart from a small body of key studies, it has yet to be fully exploited in this area. We present here an outline of the experimental method with particular focus on its application to the study of corrosive systems. This is illustrated with recent examples from the literature addressing corrosion, inhibition and related phenomena. Full article

(This article belongs to the Special Issue Corrosion Inhibition)

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