Volume 39, Issue 2

There are collective data about the scope of various corrosion inhibitors viz., polymers, plant extracts, inorganic compounds, ionic liquids, organic molecules with hetero atoms, and π-electron clouds have been reported so far on the corrosion prevention of various metals in various corrosive media. Many reviews of literature related to organic inhibitors have been accounted for their classification, application, and mechanism of their inhibition on metals. A mini-review with specific reference to quinoxaline derivatives is summarized in this manuscript.

As two-dimensional (2D) materials, graphene and hexagonal-boron nitride ( h -BN) are famous for protective coatings, because of their excellent chemical resistance, barrier property, impermeability along with thermal stability, and a large number of these properties are particularly suitable for protective coatings. However, the applications of graphene for metal protection have been limited by galvanic corrosion issues. Also, h -BN nanosheets are also explored as potential materials for corrosion protecting, especially, electrical insulation of h -BN is influential in solving electrochemical reaction and uniquely suitable to be used as an anticorrosion material. Interestingly, graphene doped h -BN exhibit outstanding functionalities in a synergic manner compare to stand-alone 2D materials. This review provides the fundamental summary of preparation methods for graphene and h -BN, meanwhile, the key challenges and future potential of protective coatings are discussed and predicted.

This paper investigated optimization of corrosion inhibitory attributes of mixed cocoa pod- Ficus exasperata (CP-FE) extracts towards mild steel in 1.5 M HCl using central composite design. Potentiodynamic polarization, linear polarization resistance and electrochemical impedance spectroscopy measurements were used for the electrochemical study. The result revealed maximum inhibition efficiency of 91.52% at temperature, inhibitor concentration, time and acid concentration of 50 °C, 5 g/L, 144 h and 0.2 M, respectively with R 2 value of 0.9429. Central composite design predicted optimum point of 70.37 °C, 3.81 g/L, 127.37 h and 0.22 M. Potentiodynamic polarization revealed extract to be mixed-type inhibitor with anodic prevalence. Electrochemical impedance spectroscopy showed that corrosion inhibition occurred via adsorption of CP-FE molecules on active sites of MS surface. Scanning electron microscopy images revealed protection of mild steel surface by adsorbed molecules of CP-FE extracts. Fourier transform infrared revealed presence of carboxyl (–COOH), unsaturated (–C-C–) and hydroxyl (–OH). Energy dispersive spectroscopy revealed presence of high iron composition on mild steel surface in the presence of mixed CP-FE extract proving its corrosion inhibition efficiency in 1.5 M HCl. Atomic adsorption spectroscopy revealed loss of Fe 2+ into free HCl solution. Generally, extract from mixed CP-FE was found as effective corrosion inhibitor for mild steel in 1.5 M HCl solution.

Coatings based on a graphene oxide–boron nitride/epoxy (GO–BN/EP) system were fabricated and applied for corrosion protection of metal substrates. GO–BN hybrid sheet synthesized by using a modified Hummers’ method had a higher lipophilicity than GO and BN. Then, GO–BN hybrid was incorporated into an epoxy coating to investigate the compactness and the corrosion protection ability of GO–BN hybrid/epoxy coating for metal substrates. The results show that GO–BN hybrid presents a desirable dispersibility in epoxy coating, exhibiting an outstanding barrier property for corrosive ions in a 3.5 wt% NaCl solution among the four systems under investigation. The present study set forth an innovative method to synthesize GO–BN hybrid in the field of corrosion protection.

The inhibition effectiveness of Punica granatum ( also called Pomegranate) extract and the synergistic effect of potassium iodide (KI) against the degradation of mild steel in 1 M HCl was studied. Potentiodynamic polarization measurement (PDP) was used in order to investigate the performance of this compound. The presence of a mixture of iodide ions (KI) and inhibitor (PG) increased the degree of surface coverage. Also, the inhibition efficiency reaches 82% at 323 K when the concentration of P. granatum (PG) is 2 mg/L with 10 mM of KI. The synergistic effect between the inhibitor and KI could be explained by the reinforcement of the layer being adsorbed onto the steel surface. The adsorption of inhibitor onto the steel surface followed the Freundlich adsorption isotherm. Characterization techniques, such as scanning electronic microscopy coupled with energy dispersive X–ray spectroscopy (SEM/EDX), Raman, and ultra-violet-visible (UV-visible) spectroscopies, confirm the adsorption of inhibitor onto the surface morphology.

To investigate the effect of interaction between two single-Si 3 N 4 particle-impingements on the repassivation of 304 stainless steel in a simulated groundwater, the corrosion current peaks of the samples during the impingement were recorded, and the micro-hardness of the substrate around the crater was tested. The results indicated that significant interactions between the two impingements were observed only when the value of distance-diameter ratio ( L/d ) was less than 1.5. With L/d being less than 1.5, the corrosion current peaks and mass losses due to the second impingements were higher than those of the first ones, and the re-passivation rates of samples during the second impingements were lower than those of the first impingements. Simultaneously, the microhardness of the substrate between the two craters was higher than that of the surface around one single crater with the same distance-diameter ratio. The mechanisms of how the L/d ratio influenced the interaction between the two impingements are also discussed.

This paper results from mutual discussions on the review ‘When do small fatigue cracks propagate and when are they arrested?’ in Corrosion Reviews, 2019; 37(5): 397–418. These discussions have arisen from the two engineering paradigms characterizing our fatigue research: (i) an aerospace research and technology remit for metallic airframes, and (ii) a materials science research programme supporting a methodology for steam turbine low pressure (LP) blade operations. In our opinion, this paper is of interest for other investigators of metal fatigue with respect to design requirements, life predictions and assessments. In more detail, the paper considers the fatigue design methodologies for airframes and steam turbine LP blades. This includes short/small fatigue cracks, fatigue crack growth thresholds, high-cycle fatigue (HCF) and very-high-cycle fatigue (VHCF), and the relevance of environmental effects (corrosion and corrosion fatigue). Graphical Abstract This paper discusses and compares the two engineering paradigms for fatigue design of (i) aircraft structures and (ii) steam turbine low pressure blades.