Figures and table of Electrochemical behavior of an aluminum alloy 2024-T3 exposed to bacteria obtained from Thailand’s environment
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The published document is related to results obtained from Microbiologically Influence Bacteria characterized by LSV and polarized EIS.
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Isolation and Identification of Bacterial Strains:The bacterial strains were obtained from the corrosion products on an aircraft's undercarriage exposed to Thailand's tropical environment. The biological sample collected was placed in a sterilized plastic container to be transported to the laboratory in a cooler. The bacterial growth was carried out inoculating aseptically in a nutritive broth (Luria Bertani, LB). The composition of the culture broth (g L-1) in water (ultra-pure, Milli-Q quality, 18.2 MΩ cm-1) consisted of 10 tryptone, 5 yeast extract, and 10 NaCl. Cultured bacteria were isolated by successive serial dilutions and conventional plating from the general enrichment conditions. Two strains were isolated and stored at -18 °C to ensure the bacterial material's purity and consistency in all subsequent experiments. Culture Media Preparation:Sterilized plates of AA2024-T3 were exposed to the medium 1 (M1 from now on), that contains (in g L-1): 0.22 (NH4)2SO4, 18.70 NaSO4, 1.20 KH2PO4, 0.23 MgSO4×7H2O, 0.25 CaCl2 × 2 H2O, and 0.58 NaCl, additionally 0.024 g yeast extract and 0.024 g tryptone. The control system was a sterile M1 (pH 4.8), while the understudy system was a sterilized M1 inoculated with bacteria. The inoculation of microorganisms was performed using 10 % v/v of the bacteria in M1, previously grown in LB broth at 27 °C overnight and pelleted. The culture was inoculated to 108 CFU mL-1. To maintain the bacterial density near to steady-state during the entire experiment, every 4 days, 70% of the medium was removed and replaced with fresh sterile M1. Then, the bacteria were re-inoculated. Electrochemical measurements were performed with a three-electrode configuration, with the AA2024-T3 being the working electrode, and placed at the bottom of the electrochemical cell, with a surface area of 16.6 cm2. A pure graphite rod (diameter, 6 mm) and a saturated calomel electrode (SCE) were used as a counter electrode and reference electrode. The electrolyte consisted of a sterile and inoculated M1, which was kept at 27 °C. The electrochemical measurements were carried out using a VSP potentiostat (Bio-Logic, USA) after one, eight, and twelve days of exposure to M1. The EOC was measured, until its stabilization, before each electrochemical measurement. The LSV tests were performed by sweeping from EOC towards the cathodic zone until reaching -145 mV and 250 mV towards the anodic region separately at a sweep rate of 0.1 mV s-1. The EIS data were performed at EOC and ηc = EOC - 50 mV, from 10 kHz to 10 mHz with 7 points per decade, and using 10 mV peak-to-peak sinusoidal potential. The Kramers-Krönig relation was utilized to adjust the frequency range analyzed until the lowest χ2 value was reached, and impedance data were fitted using a home-developed software called SIMAD (LISE UPR 15 CNRS, France). All measurements were carried out in triplicate to ensure reproducibility.