STUDY OF BIOCORROSION BEHAVIOR ON AL 6061 BY Citrobacter youngae STRAIN SKC-4 IN MARINE ENVIRONMENT

• Main Author: JEREMY (NIM : 12513045), ERIAN
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/26951
• Institution: Institut Teknologi Bandung

Ship, as one type of marine transportation and logistic vehicle, consists of parts that are of metal, for example, hulls, decks, and decorative elements. Aluminum is a metal that is commonly used as ship components due to its high corrosion resistance as a result of passive layer [Al(OH)3] formation on oxidized surface. However, aluminum which is immersed in seawater is still prone to corrosion when the passive layer is malformed due to the presence of aggressive ion such as Cland the presence of microorganisms which causes microbiologically influenced corrosion (MIC) or biocorrosion. This study was conducted to investigate the effect of the sulfate-reducing bacteria (SRB), Citrobacter youngae strain SKC-4, on aluminum 6061 alloy biocorrosion process in seawater medium which was sampled from Java sea in which sulfur content was high. <br /> <br /> <br /> <br /> <br /> A series of experiments were carried out including the preparation of materials, bacteria, and seawater medium. Materials preparation was performed for immersion test. Culture of the bacterium Citrobacter youngae strain SKC-4 was prepared by growing it in the modified-LB broth medium for 2 days and 10 hours of incubation. Furthermore, the bacterial culture (10% v/v) was introduced into seawater as a biocorrosion medium. Specimen was immersed in seawater containing bacteria for 7, 14, and 30 days. Observation was undertaken to determine corrosion rate, corrosion mechanism, and <br /> <br /> polarization resistance reduction as a result of biocorrosion of Al 6061 immersed in seawater containing bacteria. Corrosion rate was calculated based on weight loss data of immersion test, current density data from Tafel extrapolation, and polarization resistance (Rp) data from linear polarization method (LPR) measurement. <br /> <br /> <br /> <br /> <br /> Immersion test results showed that corrosion rates after 7, 14, and 30 days of immersion were 0.2865 mm/year, 0.5907 mm/year, and 0.8030 mm/year, respectively. Using Tafel extrapolation, one of the electrochemical methods, the resultsshowed that corrosion rates after 7, 14, and 30 days of immersion were 2.6257x10-8 mm/year, 7.6389x10-8 mm/year, and 1.7738x10-7 mm/year, respectively. Using another electrochemical method, LPR, the results showed that corrosion rates after 7, 14, and 30 days of immersion were 2.9745x10-8 mm/year, 3.6264x10-8 mm/year, and 2.2940x10-7 mm/year, respectively. Generally, the longer the immersion time in seawater containing the bacterium SKC-4, the higher the corrosion rate of Al 6061. The corrosion rate in seawater containing bacteria was higher than that in seawater without bacteria. EIS (electrochemical impedance spectroscopy) test revealed the polarization resistance values of 4676 ohm.m-2 (7 days of immersion), 2226 ohm.m-2 (14 days of immersion), and 846 ohm.m-2 (30 days of immersion). It appeared that the longer the immersion time in seawater containing bacteria, the lower the polarization resistance value of Al 6061. The polarization resistance value in seawater containing bacteria was lower than that in seawater without bacteria. The bacterium Citrobacter youngae strain SKC-4 formed biofilms that apparently increased corrosion rate and decreased polarization resistance value of Al 6061 immersed in seawater. FTIR and SEM-EDS mapping observations showed that the longer the specimen was immersed in seawater containing bacteria, the thicker the biofilm layer was formed on the specimen surface.