B.V. Appa Rao

Synergistic inhibition in low chloride media

Abstract Electrochemical and weight change methods were used to study the synergistic inhibition offered by Zn 2+ ions and 2 carboxyethyl phosphonic acid (2CEPA) to the corrosion of mild steel in 60 ppm chloride solutions. The surface film was found to contain Zn(OH) 2 along with iron phosphonate complex. The diffusion of iron, phosphonate complex and H + ions through this film determines the dissolution rate of iron.

Inhibition by phosphonic acids ‐ an overview

Phosphonic acids are good complexing agents. However, they are not good as inhibitors except for a very few. Synergistic inhibition is offered in the presence of metal cations like Ca2+, Mg2+, Zn2+ and others in neutral media. The zinc ion is an ideal choice. The part of zinc ions are now replaced by polymers, azoles to prepare eco‐friendly inhibitor formulations. They are also used as corrosion inhibitors in concrete, coatings, rubber blends, acid cleaners, anti‐freeze coolants, etc. Discusses the various applications of phosphonic acids and their action mechanisms.

SYNERGISTIC EFFECT OF N,N-BIS(PHOSPHONOMETHYL) GLYCINE AND ZINC IONS IN CORROSION CONTROL OF CARBON STEEL IN COOLING WATER SYSTEMS

A protective film has been developed on the surface of carbon steel in low chloride aqueous environment using a synergistic mixture of an environmentally friendly phosphonic acid, N,N-bis(phosphonomethyl) glycine (BPMG), and zinc ions. Impedance studies of the metal/solution interface indicated that the surface film is highly protective against the corrosion of carbon steel in the chosen environment. Potentiodynamic polarization studies showed that the inhibitor is a mixed inhibitor. X-ray photoelectron spectroscopic analysis (XPS) of the film showed the presence of the elements iron, phosphorus, nitrogen, oxygen, carbon, and zinc. Deconvolution spectra of these elements in the surface film showed the presence of oxides/hydroxides of iron(III), Zn(OH)2, and [Zn(II)-BPMG] complex. This inference is further supported by the reflection absorption Fourier transform infrared spectrum of the surface film. Analysis by SEM is presented for both the corroded and protected metal surfaces. Based on all these results, a plausible mechanism of corrosion inhibition is proposed.

Environmentally friendly ternary inhibitor formulation based on N,N-bis(phosphonomethyl) glycine

Abstract Studies on an environmentally friendly ternary inhibitor formulation consisting of N,N-bis(phosphonomethyl) glycine (BPMG), with Zn2+ ions as primary synergist and ascorbate ions as secondary synergist to protect carbon steel from corrosion in low chloride environment are presented in this paper. Although the binary system, BPMG–Zn2+, is an effective inhibitor, it demands relatively higher concentrations of both BPMG and Zn2+. In the present study, ascorbate was added to lower the effective concentrations of BPMG and Zn2+. The effect of addition of ascorbate is quite significant. While the binary system consisting of 20 ppm of BPMG and 30 ppm of Zn2+ accelerated corrosion of carbon steel, addition of just 25 ppm of ascorbate to the above system afforded an inhibition efficiency of 94%. The ternary inhibitor formulation is found to be effective in the pH range 5–11. The uniqueness of this system is that it has shown excellent inhibition efficiency even at pH 11, at which all the other phosphonate based formulations fail. This inhibitor system functions as a mixed inhibitor. The nature and composition of the protective film have been investigated by X-ray photoelectron spectra and Fourier transform infrared (FTIR) spectra. The mechanistic aspects of corrosion inhibition are discussed.

Self-assembled 1-octadecyl-1H-benzimidazole film on copper surface for corrosion protection

AbstractFilms of 1-octadecyl-1H-benzimidazole (OBI) have been formed on copper surface by self-assembly method. Optimum conditions viz. the solvent, concentration of OBI, immersion period and temperature for the formation of a protective film on copper have been established using impedance studies. The OBI film has been characterized by X-ray photoelectron spectroscopy, reflection absorption Fourier transform infrared (FTIR) spectroscopy, contact angle measurements and atomic force microscopy. Efficiency of the OBI film to protect copper from corrosion has been investigated in aq. HCl solution using electrochemical impedance spectroscopy, potentiodynamic polarization method, cyclic voltammetry, scanning electron microscopy and gravimetry. Results of these studies inferred that the OBI film has an inhibition efficiency in the range of 97–99% under different conditions. Polarization studies inferred that the OBI film functions as a cathodic inhibitor. Cyclic voltammetric studies showed that the film is stable even after 15 cycles, when the copper electrode is polarized to an anodic potential of 0.35 V vs. Ag/AgCl electrode. Graphical Abstract1-Octadecyl-1H-benzimidazole (OBI) film has been formed on copper surface by self-assembly. The OBI film has been characterized by XPS, FT-IR and AFM. The efficiency of this film to protect copper from corrosion has been investigated by electrochemical techniques and gravimetry. The OBI film has excellent efficiency and is quite stable.

Effect of hydrodynamics on a copper-nickel alloy rotating disc electrode in a marine environment

The impact of hydrodynamic conditions on the electrochemical corrosion behavior of a Cu90–Ni10 alloy in an artificial marine environment and a sulfide-contaminated marine environment in the absence and presence of 5-(3-aminophenyl)tetrazole (APT) is discussed. Electrochemical impedance spectroscopy, potentiodynamic polarization and cyclic voltammetry (CV) and surface analytical techniques, viz., X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), are applied to evaluate the APT performance. Both the Rct and Rfilm values are reduced with an increase in the rotation speed in sulfide-polluted marine water and without APT. Interestingly, in the presence of APT, in the absence and presence of sulfide, both the Rct and Rfilm values are increased enormously. Potentiodynamic polarization studies suggest that APT performs as a mixed inhibitor. XRD and XPS techniques suggest the presence of CuO, Cu2O, CuCl, CuS and Cu2S in seawater and sulfide-contaminated seawater in the absence of APT. However, the above products are completely absent in the presence of APT film.

Self-assembled nanofilm of 1,2-dihydro-3-(octadecylthio)benzotriazine on copper for corrosion protection

The self-assembled nanofilm of 1,2-dihydro-3-(octadecylthio)benzotriazine (DOTBT) was formed on fresh copper surface obtained by etching with 7 N nitric acid at a room temperature of 30 °C. The conditions for formation of the DOTBT nanofilm have been optimized by electrochemical impedance and electrochemical quartz crystal nanobalance (EQCN) studies. The DOTBT nanofilm on copper surface was characterized by contact-angle measurement, X-ray photoelectron spectra (XPS), reflection absorption FTIR spectra and atomic force micrographs (AFM). It is inferred that formation of DOTBT film is due to chemisorption of DOTBT on copper surface through nitrogen and subsequent complex formation between DOTBT and Cu + ions. Corrosion protection ability of DOTBT nanofilm was evaluated in dilute aqueous NaCl solution using electrochemical impedance, potentiodynamic polarization, weight-loss and XPS studies. These studies inferred that the DOTBT film protects effectively copper from corrosion. Potentiodynamic polarization studies revealed that the DOTBT film inhibits corrosion by controlling the cathodic reaction. The mechanism of corrosion protection of copper by DOTBT nanofilm is discussed in this paper.

Evaluation of Surface/Solution Interface on Carbon Steel in Contact with a Phosphonate-Based Ternary Corrosion Inhibitor System

Results of studies on interface produced on carbon steel in chloride environment containing a new ternary corrosion inhibitor formulation are presented. The surface/solution interface was developed by immersing the carbon steel in a solution containing 1-hydroxyethane-1,1-diphosphonic acid (HEDP), Zn(II) and folic acid (FA). Polarization studies indicate that the formulation is capable of affecting both the partial reactions occurring on the metal surface. Impedance studies reveal that significant changes in surface/solution interface occur as inferred by enormous increase in charge transfer resistance in the medium containing the inhibitor system. X-ray photoelectron spectroscopic studies infer presence of oxides of iron, hydroxides of iron and zinc as well as heteroleptic complex, [Fe(III), Zn(II)–HEDP–FA] in the surface film. Fourier transform infrared spectrum of the surface protective film supports the presence of these compounds in the surface film. Morphological and topographical features of the protected and unprotected metal surface recorded by scanning electron microscope and atomic force microscope respectively are presented. Consolidating the results of all these studies, mechanistic aspects of corrosion inhibition are proposed.