Investigation of the Electrochemical Breakdown Response in Sensitised AA5083 Aluminium Alloy

The light-weight aluminium alloys play an important role in reducing emissions from the transport industry. However, to take full advantage of these, the corrosion mechanisms that govern their failure need to be properly understood. Hence, the electrochemical response, especially after passive film breakdown, of the aluminium alloy AA5083 was analysed via potentiodynamic polarisation. By starting the scans at the relatively negative potential of −1.4 V (vs. SCE), the reduction of water in the electrolyte causes a localised increase in pH, leading to a preferential attack on the susceptible regions in the (sensitised) microstructure; that is, the deleterious β-Al3Mg2 along the grain boundaries. Subsequently, in the later stages of the potentiodynamic scan, these regions that have been degraded by the dissolution of β-Al3Mg2 undergo imperfect repassivation, leading them to be vulnerable to localised breakdowns. These conditions allowed for the discovery of a discernible trend after breakdown, in which AA5083 microstructures with a more extensive β-Al3Mg2 region (both in size and in amount) recorded a more rapid increase in the measured current density. In particular, the potential at which the anodic current density reached 1 × 10−4 A cm−2 was correlated with the extent of β-Al3Mg2 formed during isothermal heat-treatments. This work provides a possible pathway towards the development of an electrochemical quantification technique for the extent of β-Al3Mg2 growth, degree of sensitisation, and, ultimately, the intergranular corrosion (IGC) susceptibility of the microstructure of AA5083 components used in industrial applications.

Localised corrosion of super duplex stainless steel in synthetic NaOH-Na2S solution at different temperatures

The pitting corrosion resistance of the UNS S-32760 super duplex stainless steel (SDSS) in synthetic NaOH-Na2S solution at different working temperatures of 25, 50, and 70°C has been evaluated in the current investigation to assess the alloy behaviour under the caustic environments used in the pulp and paper industry. The temperature effect on pitting (Ep) and repassivation (Erp) potentials was studied with the Cyclic Potentiodynamic Polarisation (CPP) technique according to the ASTM G61. Results demonstrated that pitting corrosion is prone to occur when increasing alloy temperature since both pitting and repassivation potentials lean towards more negative values while the repassivation zone is reduced. Furthermore, the morphology of the found pits was determined using Scanning Electron Microscopy (SEM). The pitting corrosion mechanism for the studied super duplex stainless steel under the exposed conditions was introduced. The thiosulphate ion is attributed to be responsible for the initiation of the localised corrosion.

Chemical Adsorption Data’s, Temperature Effect and Structural Properties of Artemether-Lumefantrine Corrosion Inhibition Properties on Structural Steel in 0.62M NaCl

Chemical and marine components are faced with corrosion resulting from salty media in an application, which ends up in serious catastrophe. In an attempt to provide and curtail this challenge of toxic use of inorganic inhibitors, properties of Artemether/Lumefantrine was examined as a corrosion inhibitor for mild steel in 0.625M sodium chloride (NaCl) medium. The corrosion propagation under different inhibitor concentrations between 0-20 ml and the temperature difference of 298-323K was examined using linear potentiodynamic polarisation and open circuit potential. The structural pitting evolution was done using a scanning electron microscope (SEM) and energy-dispersive x-ray spectroscopy (EDS) analyses. From the data, the activation energy of the corrosion reaction increased with increasing inhibitor concentration, suggesting that it inhibits corrosion by increasing the energy required to initiate the corrosion reaction. The Gibbs free energies of adsorption fall within the range of-10.08 and-13.87 kJ/mol, which is greater than-20 kJ/mol; thus, the artemether-lumefantrine inhibitor exhibited physical type adsorption. The values of the free energy of adsorption were all negative. The Langmuir Isotherm seems to perform exceptionally well with a correlation efficiency of 0.975 against all other isotherm fits.

Corrosion Inhibition of Carbon Steel Using Palm Oil Leaves Extract

Palm oil (Elaeis guineensis) leaves extract was investigated on its potential to inhibit carbon steel corrosion via weight loss and potentiodynamic polarisation methods. Corrosion inhibition of carbon steel using palm oil leaves extract was determined at various temperatures, salinities, and concentrations. The inhibition efficiency increased with the increasing of inhibitor concentration but decreased with the rise in temperature. The highest inhibitor efficiency was 83.70% with a corrosion rate of 0.44 mm/yr which was obtained at zero salinity (in distilled water) with 25% of inhibitor concentration at 303 K. The results obtained proved that the extract solution from palm oil leaves can be used as an effective inhibitor of carbon steel in seawater.

Red clover (Trifolium pratense L.) honey: volatiles chemical-profiling and unlocking antioxidant and anticorrosion capacity

Headspace solid-phase micro-extraction (HS-SPME) and ultrasonic solvent extraction (USE) were used for red clover honey volatiles extraction. The extracts were analysed using gas chromatography and mass spectrometry (GC-MS). Lilac aldehyde isomers dominated in the headspace (individual range from 7.6 % to 21.4 %) followed by phenylacetaldehyde (10.1-31.2 %) and benzaldehyde (7.0-15.7 %). Higher aliphatic alcohols and hydrocarbons were the predominant constituents of the honey extracts. The honey and its extracts exhibited rather weak anti-radical activity (DPPH assay) and total antioxidant activity (FRAP assay). On the other hand, the honey’s inhibitive properties towards the corrosion of AA 2017A alloy in NaCl solution (potentiodynamic polarisation and potentiostatic pulse measurements) revealed the honey to be a very good anodic inhibitor (efficiency up to 76 %) while the honey extracts (USE) showed better inhibition efficacy.

Copper corrosion behaviour in acidic sulphate media in the presence of 5-methyl-1H-benzotriazole and 5-chloro-1H-benzotriazole

The influence of 1H-benzotriazole, 5-methyl-1H-benzotriazole and 5-chloro-1H-benzotriazole on copper corrosion in an acidic sulphate medium was studied, as well as the influence of chloride ions on the corrosion behaviour of copper. The methods used were potentiodynamic measurements, open circuit potential and mass loss. The results show that the examined compounds possess good inhibitory properties in an acidic medium. The potentiodynamic polarisation results indicate that the degree of copper protection against corrosion depends on the concentration of Cl