Self-Assembling Monolayers of Stearic Acid in Protection of Steel

Carbon steel corrodes severely in presence of sodium chloride and it needs additional protection to be used in marine environments. This work investigates the possibility of using a layer of stearic acid as protection for carbon steel. Stearic acid was applied on the steel by two types of treatments: chemical preparation - by immersion of a steel sample in the SA solution and electrochemical preparation – by imposing a corresponding potential to the system. The results have shown that although both treatments result in obtaining an ordered aliphatic monolayer and both treatments increase the hydrophobicity of the surface, protection that the electrochemical preparation offers is stable in time, while the protection the chemical preparation offers is not. This work is licensed under a Creative Commons Attribution 4.0 International License

Influence of Imidazole Derivatives on Copper Corrosion

U ovome radu prikazani su rezultati istraživanja inhibitorskog djelovanja netoksičnih derivata imidazola na proces korozije bakra u w = 3 % NaCl. Elektrokemijska ispitivanja metodom potenciodinamičke polarizacije pokazala su da svi istraživani spojevi smanjuju brzinu korozije bakra, pri čemu njihova djelotvornost raste s povećanjem molekulske mase spoja. Osim molekulske mase bitan utjecaj na inhibitorska svojstva spoja ima i priroda supstituenta. Spojevi s alkilnim supstituentom na imidazolnom prstenu imaju manju djelotvornost od spojeva s arilnim supstituentom. Djelotvornost alkilnih derivata imidazola ne mijenja se s temperaturom, dok djelotvornost arilnih derivata opada s povišenjem temperature. Osim toga, alkilni derivati imidazola pokazuju veći utjecaj na katodnu reakciju korozijskog procesa, dok arilni derivati imidazola pokazuju veći utjecaj na anodnu reakciju. Dodatna elektrokemijska (EQCM i EIS) te spektroskopska ispitivanja pokazala su da i između dva najdjelotvornija i strukturno vrlo slična spoja, 1-fenil-4-metilimidazola i 1-(p-tolil)-4-metilimidazola, postoje znatne razlike u mehanizmu kočenja korozijskog procesa. Dok prvi inhibitor usporava korozijski proces postupnim stvaranjem gustih mrežastih struktura, drugi inhibitor se vrlo brzo adsorbira na površinu metala, pri čemu nastaje tanki zaštitni film.Inhibiting efficiency of non-toxic imidazole derivatives (presented on Figure 1), as copper corrosion inhibitors in w = 3 % NaCl solution, was studied in the present work. Electrochemical investigations performed by potentiodynamic polarization measurements have shown that all studied compounds decrease the rate of copper corrosion while their inhibiting efficiency increases with molecular mass (Table 1). Except the molecular mass, the nature of the supstituent significantly influences the inhibiting property. Compounds containing alkyl supstituent show lower inhibiting efficiency than aryl containing imidazoles, but their efficiency is temperature independent while the efficiencies of aryl supstitued imidazoles slightly decrease with the increase of temperature (Fig. 3). Furthermore, alkyl imidazoles influence more on cathodic corrosion reaction, while aryl imidazoles have more influence on anodic corrosion reaction. Additional electrochemical (EQCM and EIS) and spectroscopic investigations have shown that, even between the two most efficient corrosion inhibitors, 1-phenyl-4-methylimidazole and 1-(p-tolyl)-4-methylimidazole, exist important differences in the mechanism of retardation of the corrosion process. The inhibitor that contains the tolyl substituent decreases the corrosion rate of copper due to the formation of thin layer of adsorbate, while in the case of 1-phenyl-4-methylimidazole, formation of thick layer can be followed with time (Fig. 4). From EIS (Electrochemical Impedance Spectroscopy) studies, it was observed that these inhibitors significantly increase absolute impedance of copper which shows that they efficiently protect copper from corrosion. In the case of 1-phenyl-4-methylimidazole absolute impedance increases in time (Fig. 5 and 6) which means that the protective layer is slowly forming on the metal surface. Studies performed in the presence of 1-(p-tolyl)-4-methylimidazole showed that already after short immersion time (Fig. 5) very protective surface film is formed and it remains stable in time (Fig. 6.) Investigations performed by SEM and AFM measurements confirm that 1-phenyl-4-methylimidazole forms three-dimensional protective surface layer while in the presence of 1-(p-tolyl)-4--methylimidazole copper surface is protected by a thin inhibitor film

Corrosion Protection by Octadecylphosphonic Acid in Flow Conditions

The aim of this work was to examine the influence of the flow rate of corrosive media on the stability of self-assembled films of octadecylphosphonic acid on copper-nickel alloy and stainless steel. The studies were conducted in river and seawater in a laboratory scale flow system. Corrosion behaviour of protected and unprotected alloys was examined by electrochemical techniques, electrochemical impedance spectroscopy, and polarization measurements. The results show that octadecylphosphonic acid films can efficiently protect copper-nickel and stainless steel from corrosion in flowing natural waters. The flow of corrosive media had the highest influence on the stability of films on CuNi in seawater, while in all other studied cases, the protective properties of ODPA film changed insignificantly with the change of the flow rate

Protective films of stearic and octadecylphosphonic acid formed by spray coating

Spray coating formation of stearic and octadecylphosphonic acid films for corrosion protection of cupronickel alloy was studied in this work as a more practical alternative to widely studied dip-coating method. Protective properties of organic films formed under various experimental conditions were examined by electrochemical studies in 3% NaCl solution as a corrosive medium. Polarization resistance measurements as well as electrochemical impedance spectroscopy were employed to follow in time the corrosion behaviour of cupronickel alloy modified by studied organic acids. It was found that among examined experimental parameters, time elapsed between two sprays and number of sprays have the strongest influence on the film stability and its protective properties. This study confirmed that it is possible to form by spray coating the films of stearic and octadecylphosphonic acid with protective properties that resemble to those of the films prepared by dip-coating method. Differences in corrosion behaviour of samples protected with stearic and octadecylphosphonic acid were attributed to difference in the bond strength between substrate and each organic acid. Studied samples were also examined by the scanning electron microscopy. Fourier transformed infrared spectroscopy studies showed that crystalline structure dominates in studied films, while contact angle measurements confirmed that modified cupronickel alloy surface exhibits hydrophobic properties

Benzimidazole Derivatives as Copper Alloy Corrosion Inhibitors

Seawater is a corrosive medium that adversely affects on the metallic structures. For that reason, it is often desirable to use some type of corrosion protection to extend the life of structures. The aim of this work was to examine the possibility of CuNi alloy protection in artificial seawater by four benzimidazole derivatives: 2-amino-5(6)nitrobenzimidazole, 2-amino-5-(6)-cyanobenzimidazole, 2-aminobenzimidazole, 2-amino-5(6)-(2-imidazolinyl)benzimidazole hydrochloride. The corrosion studies conducted by polarization measurements after 1 h of immersion in inhibitor solution showed that the most effective inhibitor is 2-amino-5(6)-nitrobenzimidazole. The electrochemical tests were also performed in time by the means of electrochemical impedance spectroscopy for the two most effective inhibitors. The surface of samples was analyzed by scanning electron microscopy and ATR-FTIR spectroscopy. It was concluded that the efficiency of studied inhibitors increases with prolonged exposure of the CuNi alloy to inhibitor solutions as well as with the increase of inhibitor concentration. This work is licensed under a Creative Commons Attribution 4.0 International License

Electrochemical Characterization of Bronze Exposed to Outdoor Atmosphere

The aim of this work was to examine corrosion behaviour of bare and artificial patinated bronzes during exposure to urban outdoor atmosphere. Studies were conducted on copper and two different bronzes in order to evaluate the influence of substrate composition on patina composition and electrochemical behaviour. Additionally, two different patination methods were compared. Corrosion behaviour was examined using electrochemical impedance spectroscopy with gel-electrolyte electrochemical cell. The composition of patina was determined by ATR-FTIR spectroscopy. The obtained results showed that all studied artificial patinas initially decrease the corrosion resistance of copper and bronzes but in time their corrosion resistance improves, and even for certain combinations, artificial patina-bronze corrosion resistance is higher than that of naturally patinated bronze. This work is licensed under a Creative Commons Attribution 4.0 International License