Volume 40, Issue 5

The review article summarizes various ionic liquids (ILs) used as corrosion inhibitors reported in the literature during the preceding five years (2016–2020) for corrosion of carbon steel in acidic solutions. The ILs are a green and sustainable choice for corrosion inhibition as compared to natural extracts as corrosion inhibitors due to lack of stability which restricts their application at the industrial level. The review discusses the inhibition efficiency of the ILs as corrosion inhibitors; the evaluation techniques like weight-loss method, potentiodynamic polarization, electrochemical impedance spectroscopy, etc., used for determination of inhibition efficiency and plausible mechanism of inhibition, adsorption isotherms are discussed. The review affirms that ionic liquids serve as excellent green corrosion inhibitors for carbon steel dissolution in acidic media. Most of the reported inhibition efficiency values ranged between 80 to 90% at minute concentrations which is valuable. The scope for further improvements is given for the benefit of readers.

Replacing or servicing corroded reinforced concrete structures requires careful consideration of the rate of corrosion of the embedded rebar. Corrosion rates are usually measured using monitoring techniques, but these techniques may not always give reliable results due to the effect of factors called rate influencers. Though the consideration of rate influencers does not entirely alleviate the problem, monitoring them during measurements will significantly reduce the probable error. Hence, this paper compares the experimental results of prior studies with an effort to draw out the best corrosive environment for the efficient working of a few widely used monitoring techniques and presents a list of some major rate influencers that need concern for the accurate evaluation of corrosion. A literature review is performed to achieve the above objectives. The Monitoring techniques considered in this study are linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), galvanostatic pulse technique (GPT), and half-cell potential (HCP).

Graphene and its derivatives have attracted much interest as corrosion-resistant coatings for magnesium alloys since 2014, when the first reports appeared in the literature. The interest in the use of such carbonaceous compounds to protect magnesium and its alloys from corrosion relies on a set of attributes such as chemical inertness, and high surface area. To support the development of optimized graphene-based films it is imperative to expand the current knowledge toward a deeper understanding of corrosion mechanisms and their interaction with practical aspects related to coating deposition and morphology. In the present work, graphene-based coatings for magnesium alloys are reviewed. We explored the correlation between coating architecture, deposition methods and materials selection using the Ashby approach. The results of the materials selection process revealed that composite coatings consisting of an inorganic matrix obtained by plasma electrolytic oxidation of magnesium alloys and graphene oxide nanosheets as blocking agents can provide surfaces with high corrosion resistance in sodium chloride solution. For biomedical applications, composite coatings consisting of a mixture of organic matrices such as chitosan and graphene oxide as reinforcing particles are attractive candidates. The results are discussed based on coating architecture and its interplay with the corrosion properties.

The oil and gas industry worldwide is experiencing problems of vandalism and mechanical deterioration due to corrosion in its various pipeline transport systems, a drop in the price of hydrocarbons due to the COVID-19, limitation of maintenance processes. This article provides a contribution original to the knowledge and management of a pipeline transportation system (PTS), without an immediate high impact that would help reduce property loss due to corrosion, through the development of intelligent evaluation models that combine field data, laboratory, and cognitive knowledge in a case study in Mexico. The research is divided into Part 1: modeling, a Fuzzy expert system (FES) unified the knowledge of corrosion specialists and mechanical integrity studies (MIS) and identified evolutionary corrosion patterns with reliability of 0.9029. An artificial neural network (ANN) supported by statistics and metallography establishes test reliability of 0.9556 and determines the corrosion inhibition capacity (C) of Mexican hydrocarbon mixtures based on their properties compared to carbon steel. Part 2: analysis of the operational and economic risk of the PTS under corrosive effects, using Monte Carlo simulation (MCS) estimates various financial scenarios considering corrosive profiles of soils, supply, demand, and inflation.

The study of a stir cast Al356-Nb 2 O 5 ) P composite immersed in third-generation microalgal-derived biodiesel blends with enhanced plasma electrolyte oxidation surface modification revealed the corrosion susceptibility and possible by-product formation. The effect of (oxide) P reinforcement and mixed-oxide surface coatings were studied separately and cumulatively. Samples were immersed in different biodiesel and petrodiesel blends for up to 3000 h, and their corrosion and electrochemical behavior was studied. Although some weight change was recorded in all samples, the corrosion rates significantly decreased from 1.8 to 1.3 by 10 wt% Nb 2 O 5 ) P reinforcement, which further decreased 10 times after surface modification. Electron microscopy revealed primary fine-grained microstructure with low porosity content of fine and needlelike dendritic structures in composites and irregular volcanic with scattered micropores and microcracks in surface-modified composites that changed to corrosion spots and flake-covered microcracks after immersion.

An epoxy with 7% polyaniline (PANI) powder coating by electrostatic deposition is proposed to enhance the corrosion resistance of AZ61 magnesium alloys. The coating thickness is varied from 85 to 130 microns, and the results are compared to the corrosion resistance of epoxy coated and uncoated AZ61 magnesium alloy. The surface characterization and corrosion behaviour of AZ61 magnesium alloy + epoxy/PANI coating are examined using X-ray photoelectron spectroscopy, salt spray test, potentiodynamic test and Fourier transform infrared spectroscopy. It is observed that the polymer coating protects the base metal against corrosion and the corrosion resistance increases with coating thickness. The corrosion rate of the uncoated, 130 µm coating thickness of epoxy coated and epoxy/PANI coated AZ magnesium alloy is observed to be 0.5379, 0.0869 and 0.0372 mm/year, respectively. The corrosion resistance of epoxy/PANI coating is superior to the epoxy coating. The increase in corrosion resistance of the epoxy/PANI coated AZ61 alloy is attributed to the physical insulation and suppression of magnesium dissolution.

Coatings of metal surfaces is a convenient and low cost anti-corrosion issue, while corresponding defects like poor heat and corrosion resistance are also obviously hinder its further application. Hence, continuously developing new and efficient coatings is of great significance to improve anti-corrosion for metals. In this study, silicone-acrylic resin was modified by two-dimensional lamellar structure of graphene oxide (GO) though direct co-blending to improve the anti-corrosion. Then, polyaniline/graphene oxide (PANI/GO) composites was prepared by in-situ polymerization method, which innovatively achieved the combination of flake and fibrous materials to fill the voids generated when the coating is cured into a film, and enhance the density and the anti-corrosion performance of the coating. The result showed that the coating modified by PANI/GO had the better thermal stability, which T 5% and T max are increased by 44 and 5 °C, respectively. Electrochemical impedance spectroscopy (EIS) and Tafel polarization curves were employed to analyze anticorrosion performance of modified coatings explored in 3.5 wt% NaCl aqueous solution. The coating with 20 wt% GO in PANI/GO has the best corrosion resistance with corrosion potential of −0.14 (V vs. Hg/Hg 2 Cl 2 ), corrosion current density of 1.8 × 10 −11  A cm −2 , polarization resistance of 6.06 × 10 10  Ω cm 2 , and lower corrosion rate of 4.18 × 10 −7  mm year −1 after immersion for 60 day.