Investigating metal-inhibitor interaction with EQCM and SVET

Significance 

Copper as well as its alloys have seen modern world applications in the form of building elements for applications in micro-electronics. Copper (Cu) is quite resistant to corrosion in neutral environments as well as sulfur dioxide and chloride free environments, protected by a layer of copper dioxide, also known as patina. Unfortunately, Cu is susceptible to corrosion when exposed to aggressive media, when the patina is converted to other corrosion products.

A number of methods have been implemented to mitigate metallic corrosion. The use of organic and inorganic inhibitors is one of them. Organic inhibitors are compounds that are normally applied in small concentrations and have the potential to efficiently minimize the rate of corrosion. Compounds belonging to the azoles group contain sulfur and/or nitrogen heteroatoms that have great affinity to Cu and its alloys, serving as the anchoring point between these organic molecules and copper surface. Because of this attraction, the azoles are considered as effective corrosion inhibitors for Cu in an array of aggressive environments.

Inhibitor selection is based usually on gravimetric determination of metal dissolution rate, but unfortunately this method provides insufficient information about the complex interactions between the inhibitor, metal surface, and the corrosive media. Therefore, in order to optimize inhibition efficiency, the mechanism of interaction with the metal system must be adequately understood. However, this approach calls for the application of electrochemical methods, as well as surface analysis.

Electrochemical quartz crystal microbalance (EQCM) is an electrochemical method that allows for the acquisition of the relevant data about the adsorption of molecules on metallic surfaces with microscale resolution, therefore, enabling the characterization of their adsorption kinetics. The method works by applying an oscillatory electrical field to a quartz resonator placed between two electrodes.

Prof. Dr. Lucien Veleva and Dr. J.A. Ramírez-Cano at CINVESTAV-Merida, Mexico in collaboration with Dr. Bibiana M. Fernández-Pérez and Prof. Ricardo M. Souto at University of La Laguna in Spain, characterized the electrochemistry of metal-inhibitor interaction of 3-amino-1,2,4-triazole (ATA) using open circuit potential measurements (OCP, free corrosion potential), scanning vibrating electrode technique (SVET), and electrochemical quartz crystal microbalance technique (EQCM). Their research work is published in peer-reviewed journal, Materials and Corrosion.

The authors treated the surfaces of gold (Au) and copper micro-electrodes, separately and electrically connected in a bid to form a galvanic Au-Cu pair with ATA, considered as a corrosion inhibitor. The basis for selecting this galvanic pair was based on the current trends in microelectronics, where Cu and Au made components are in close proximity. They tested the surface reactivity of the inhibitor-modified metals in diluted chloride solution (1 mM NaCl).

The presence of the azole inhibitor ATA on Au and Cu surfaces was observed to modify the open circuit potentials of both metals. The inhibitor shifted the free corrosion potential (OCP) of gold to a more positive value, while that of copper became slightly more negative. In view of these facts, the authors concluded that the inhibitor ATA was not copper corrosion inhibitor.

The free adsorption energy computations, based on the recorded frequency response performed with the electrochemical quartz crystal microbalance, indicated that the inhibitor ATA was physisorbed on both metal surfaces. Considering that the main protection mechanism related to this organic inhibitor is the development of a physical barrier between the metal surface and the aggressive media, the efficiency of a physisorbed film was lower-ranking. As the inhibitor ATA (3-amino-1,2,4-triazole) was not chemisorbed, its adhesion forces to the metal surface wasn’t strong, compromising its ability to act as an effective barrier between the metal and the aggressive environment.

 metal-inhibitor interaction with EQCM and SVET-Advances in Engineering

About the author

J.A. Ramírez-Cano has a Bachelor degree in Chemical Engineering at the Universidad Veracruzana, Mexico (2010), Master degree (2013) and Ph.D. (2017) in Physical Chemistry at CINVESTAV-Merida, Mexico, where he currently holds the position of Associate Professor (2017). His research direction is the study of corrosion behaviour of metals in aggressive environments and application of corrosion inhibitors. He mainly focuses in the electrochemical corrosion of metals in marine environments, adsorption processes of organic compounds employed as corrosion inhibitors and their performance, employing techniques, such as Electrochemical Impedance Spectroscopy (EIS), Electrochemical Quartz Crystal Microbalance (EQCM), Scanning Vibrating Electrode Technique (SVET) and Scanning Electrochemical Microscope (SECM). He has published several articles in international journal and contributed in scientific meetings.

About the author

Dr. Bibiana M. Fernández-Pérez got her PhD in Chemistry from the University of La Laguna, Spain, in 2017. Her PhD thesis was focused on the corrosion electrochemistry of different metals exposed to ennvironments presenting variety in aggressivity level.  The studies were performed with both classical (EIS) and more current techniques in situ (SECM, SVET, combined SECM-AFM). During the period of her PhD, she was invited for stays in Institut für Analytische und Bioanalytische Chemie (Universität Ulm, Germany) and in the Chemical Institute, Faculty of Science (University of Pecs, Hungary). She has published more than 25 international papers and contributed in 36 scientific meetings.

About the author

Prof. Dr. Lucien Veleva is majored in Electrochemistry (Eng.) in Sofia, Bulgaria, University of Chemical Technology and Metallurgy. Her PhD is done in Institute of Physical Chemistry, Bulgaria, 1981. After that was working as researcher in the “Institute for Protection of Metals from Corrosion” (Sofia, Bulgaria), as a head of National Laboratory for Testing of Corrosion. Since 1994 is invited as Associated Professor at Applied Physics Department (Center for Investigation and Advanced Study – CINVESTAV, Mexico), teaching in Master and Doctor Degrees programs in Physical Chemistry, and also as adviser of thesis.

As Full Professor her area is electrochemistry of corrosion processes, localized corrosion, interfacial electron-transfer kinetics, application of scanning micro-electrochemical microscopy techniques, atmospheric corrosion, marine corrosion, soil corrosion, reinforced steel corrosion, accelerated tests and models for simulation of corrosion process, corrosion inhibitors, paint coatings, electrodeposition of metal coatings (composites), sensors for monitoring of corrosion process, biofouling on materials, degradation of polymers and wood´s materials. Lucien Veleva is an active working member and expert of ASTM, NACE and ISO committees.

She is also member of ECS, International Societies of Electrochemistry (ECS and ISE), Mexican Academy of Science. In 2011 she received Doctor Honoris Causa (UABC, Mexico); in 2012 – Francis La Que, Award of ASTM (Committee G01, USA); in 2013 – NACE International Distinguished Career Award, for her outstanding contribution to the field of corrosion science and engineering and for exemplary technical and leadership expertise. She has more than 100 articles in international journals, chapters in international books, book on corrosion and material degradation (in Spanish), and 4 Bulgarian Patents .

About the author

Prof. Ricardo M. Souto (B. Sc. and Ms Sc. Universidad de La Laguna, Spain. Ph.D. in Chemistry, Utrecht University, The Netherlands, 1987) is Full Professor in Physical Chemistry at the University of La Laguna (Canary Islands, Spain) since 2008. He was Director of the Department of Physical Chemistry from 2010 to 2012.

He is the Head of the Electrochemistry and Corrosion Group at the Institute of Material Science and Nanotechnology of the University of La Laguna (IMN). Director of projects on corrosion science and engineering (passivity and localized corrosion, galvanic corrosion, corrosion inhibition, atmospheric corrosion, corrosion protection by functionalized surface coatings), design and application of scanning microelectrochemical microscopy techniques, biomaterials characterization, and water remediation.

He is a fellow of The Royal Canarian Academy of Sciences (Spain), and active member of The Electrochemical Society (ECS), the International Society of Electrochemistry (ISE), and the Royal Spanish Society of Chemistry (RSEQ). Author of more than 200 publications.

Reference

J. A. Ramírez-Cano, L. Veleva, R. M. Souto, and B. M. Fernández-Pérez. Investigating metal-inhibitor interaction with EQCM and SVET: 3-amino-1,2,4-triazole on Au, Cu and Au–Cu galvanic coupling. Materials and Corrosion issue 69 (2018), pages 115–124.

 

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