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The addition of synthetic corrosion and scale inhibitors in a recirculating cooling water system is a well-known method to defeat corrosion and scale problems. In this work, we utilize the extract from cassava leaf, which is agricultural waste in Thailand as a green inhibitor. Corrosion inhibition efficiency with using cassava leaf extract (CLE) for mild carbon steel was investigated in a simulated cooling water solution under both stagnant and hydrodynamic conditions. A mock-up of a recirculating cooling water system was custom-built to imitate the hydrodynamic conditions used in industry. Effects of CLE concentration (0, 50, 100, 200, 400, 600, and 800 ppm) and temperature (35 °C, 45 °C, and 55 °C) on corrosion inhibition efficiency were investigated. Increasing the CLE concentration increased its inhibition efficiency. In the case of stagnant conditions, the CLE showed a corrosion inhibition efficiency of 97.4% with 800 ppm CLE at 35 °C. The CLE performed as an anodic inhibitor. A decrease in inhibition efficiency was observed when the temperature was increased. For the hydrodynamic conditions with a flow rate of 34 L min−1 at 55 °C, a corrosion inhibition efficiency of 75.7% was seen with 200 ppm CLE. A scale inhibition efficiency of the CLE was investigated at concentrations of 0, 200, 800, and 2000 ppm. A 76.1% CaCO3 scale inhibition efficiency was obtained with 2000 ppm CLE. A change in the CaCO3 morphology due to the adsorption of the CLE inhibited scale formation.

Blistering is one of the major issues in processed canned coconut milk that contain several food additives. The goal of this work is to investigate the effect of five different food additives, guar gum, sodium carboxymethyl cellulose (CMC), polysorbate 60 (tween 60), citric acid (C6H8O7), and sodium metabisulfite (Na2S2O5), on blister formation in epoxy-phenolic coated tinplate cans using electrochemical impedance spectroscopy (EIS) and surface microscopy. Cathodic stripping at −6 V (Ag/AgCl) for 30 min was applied in order to provoke blisters. The results revealed that the sterilizing process deteriorated the coating performance, however, without food additives, blisters did not form even after an applied potential. Na2S2O5 and CMC were the most aggressive food additives for which blisters were observed for both non-sterilized and sterilized conditions. Na+ ions, together with water and oxygen in the solution, permeated through the coating initiating and accelerating the blister formation.

Purpose The aim of this work was to investigate how Andrographis paniculata (Burm.f.) Wall.ex Nees extract affected the corrosion of low-carbon (C) steel in 0.1M HCl. Design/methodology/approach The Andrographis paniculata (Burm.f.) Wall.ex Nees was extracted into distilled water at 70°C for 1 h. The corrosion inhibition efficiency of the extract was determined in 0.1M HCl using weight loss measurements, potentiodynamic polarization and electrochemical impedance spectroscopy. The effects of extract concentrations and of temperature were investigated. Findings The Andrographis paniculata (Burm.f.) Wall.ex Nees extract could inhibit the corrosion process of low-C steel in 0.1M HCl. With the extract concentration of 1 g/l, an inhibition efficiency of 96.3 per cent was obtained. The extract acted as an anodic inhibitor. The adsorption process of the extract was physisorption and it followed the Langmuir adsorption isotherm. Originality/value This paper revealed that Andrographis paniculata (Burm.f.) Wall.ex Nees cultivated in Thailand, which was extracted using a simple and environmentally friendly method, could act as a very good green corrosion inhibitor for low-C steel in 0.1M HCl solution.

PurposeThe purpose of this paper is to understand the effect of pressurized steam on surface changes, structures of intermetallic particles and corrosion behavior of AA1050 aluminium.Design/methodology/approachIndustrially pure aluminium (AA1050, 99.5 per cent) surfaces were exposed to pressurized steam produced from a commercial pressure cooker at the maximum temperature of 116oC for 10 min. Surface morphology was observed using SEM‐EDX and FIB‐SEM. Phase identification and compositional depth profiling were investigated using XRD and GDOES, respectively. Potentiodynamic polarization measurements were used to study corrosion behavior.FindingsA 590 nm boehmite oxide layer was generated on AA1050 associated with partially dissolved and/or fallen off Fe‐containing intermetallic particles after exposure to pressurized steam. A significant reduction (25 times) in anodic and cathodic reactivities was observed due to the formation of the compact oxide layer.Originality/valueThis paper reveals a detailed investigation of how pressurized steam can affect the corrosion behaviour of AA1050 aluminium and the structure of Fe‐containing intermetallic particles.

PurposeThe purpose of this investigation is to understand the structure of trapped intermetallics particles and localized composition changes in the anodized anodic oxide film on AA1050 aluminium substrates.Design/methodology/approachThe morphology and composition of Fe‐containing intermetallic particles incorporated into the anodic oxide films on industrially pure aluminium (AA1050, 99.5 per cent) has been investigated. AA1050 aluminium was anodized in a 100 ml/l sulphuric acid bath with an applied voltage of 14 V at 20°C ±2°C for 10 or 120 min. The anodic film subsequently was analyzed using focused ion beam‐scanning electron microscopy (FIB‐SEM), SEM, and EDX.FindingsThe intermetallic particles in the substrate material consisted of Fe or both Fe and Si with two different structures: irregular and round shaped. FIB‐SEM cross‐sectioned images revealed that the irregular‐shaped particles were embedded in the anodic oxide film as a thin strip structure and located near the top surface of the film, whereas the round‐shaped particles were trapped in the film with a spherical structure, but partially dissolved and were located throughout the thickness of the anodic film. The Fe/Si ratio of the intermetallic particles decreased after anodizing.Originality/valueThis paper shows that dual beam FIB‐SEM seems to be an easy, less time consuming and useful method to characterize the cross‐sectioned intermetallic particles incorporated in anodic film on aluminium.

Corrosion behaviour of the banded structure known as ‘onion ring’ in the nugget of friction stir weld AA2024-T351 was investigated to find the relation to microstructure. A micro-electrochemical cell with a 50 μm diameter glass pipette tip was used for electrochemical measurements. It was found that onion rings consisted of two bands: ‘dark’ bands that contain fewer constituent particles but show extensive precipitation of S phase and ‘light’ bands that contain fewer S phase precipitates but greater numbers of constituent particles. Electrochemical results showed that the light band has more noble (less active) open circuit potential compared to the dark band. Microstructurally, this is due to the lower number of S precipitates and therefore the possibility of higher Cu solid solution within the band compared to that of the dark band.

The effect of atmospheric corona discharge on AA1050 aluminium surface was investigated using electrochemical polarization, SEM-EDX, FIB-SEM, and XPS. The corona treatment was performed with varying time (1, 5, and 15 min) in atmospheric air. A 200 nm oxide layer was generated on AA1050 after the 15 min air corona treatment. A significant reduction in anodic and cathodic reactivities was observed starting from 1 min exposure, which further decreased with prolonged exposure (15 min) and after delayed testing (after 30 days). The reduction in surface reactivity is due to the formation of thicker and denser oxide film.

Cryogenic cooling with CO2 was applied during friction stir welding of AA2024-T351 in order to reduce the temperature increase during welding, and thus improve the corrosion resistance of the weld. The effect of cryogenic cooling on corrosion susceptibility was investigated with gel visualisation, immersion tests and local electrochemical measurements. The most susceptible area for both uncooled and cooled welds was in the heat-affected zone (HAZ) region, which showed intergranular attack. Cryogenic cooling had no detectable influence on the degree of anodic reactivity in the weld region. However, it did decrease the width of the reactive HAZ.

The effect of welding parameters (rotation speed and travel speed) on the corrosion behaviour of friction stir welds in the high strength aluminium alloy AA2024–T351 was investigated. It was found that rotation speed plays a major role in controlling the location of corrosion attack. Localised intergranular attack was observed in the nugget region for low rotation speed welds, whereas for higher rotation speed welds, attack occurred predominantly in the heat-affected zone. The increase in anodic reactivity in the weld zone was due to the sensitisation of the grain boundaries leading to intergranular attack. Enhancement of cathodic reactivity was also found in the nugget as a result of the precipitation of S-phase. The results were compared with samples of AA2024–T351 that had been heat treated to simulate the thermal cycle associated with welding, and with samples that had been exposed to high temperatures for extended periods to cause significant over-ageing.

The corrosion susceptibility of friction stir welds in AA2024-T351 was found to vary with the weld processing parameters. Corrosion attack was investigated with in situ X-ray tomography, which showed how the penetration of corrosion into the interior of the structure varied with weld microstructure. The susceptibility to corrosion was related to the degree of overageing by comparing the corrosion behaviour to samples of the base alloy that had been aged at different temperatures. A systematic increase first in the anodic reactivity and then the cathodic reactivity of the overaged structures with temperature can be used to predict the location of the region of the weld with the highest susceptibility to corrosion. Similar investigations were made for a dissimilar weld between AA2024 and AA7010. Laser surface melting produces a thin homogeneous melted and rapidly solidified layer over the weld surface leading to a substantial improvement in corrosion resistance.

The corrosion behaviour of a dissimilar metal friction stir weld between AA2024–T351 and AA7010–T7651 was investigated. Gel visualisation and immersion tests were used to examine the effect of galvanic coupling between the two components. A microelectrochemical cell with a 400 μm diameter glass tip was used to measure the anodic and cathodic reactivities at different positions in the weld region as well as in the base alloys. It was found that the net anodic attack was in the 7010 alloy with the highest susceptibility in the nugget region. The nugget region of 2024 was protected by its high net cathodic reactivity owing to the precipitation of S phase particles.