Understanding the Phenomenon of Biocorrosion on Uncoated and Coated AA-2024

Microorganisms have a strong tendency to colonize solid surfaces, leading to a complex microbial community that strongly adheres to the substrate, called biofilm.  Biofilms are detrimental to the underlying substrates, causing physical degradation or biodeterioration of the metal surfaces. This phenomenon is widely recognized as biocorrosion or microbiologically influenced corrosion. Among the many microorganisms which induce the degradation or corrosion of metallic materials, Pseudomonas is one of the most studied and it is associated with corrosion of aluminum and its alloys.

In this work microbiologically influenced corrosion of an aluminium alloy, AA-2024, in the presence of Pseudomonas aeruginosa was studied.

In order to understand the mechanism by which the bacterium promotes corrosion in AA-2024, bacteria were cultured for different times in the presence of AA-2024 alloy samples. The morphology of the metallic surfaces was studied by optical microscopy and the bacterial population, living or dead, was examined in a confocal microscope. Localized corrosion was followed by further observations of metallic sections after immersing in the bacterial culture for defined time intervals. Susceptibility to corrosion was assessed by potentiodynamic measurements, and bacteria-substrate interaction was followed by Atomic Force Microcopy (AFM).

The results revealed that the presence of pseudomona aeruginosa catalyze corrosion. The participation of catalase in increasing the cathodic reaction kinetics and consequently, the global corrosion process was demonstrated by electrochemical measurements using cobalt phtalocyanine modified electrodes, obtained in the absence and presence of the bacteria. In addition, from atomic force microscopy, bacterial cells within the biofilm exhibited high adhesion strength to the metal substrate. Corrosion events correlates with the hydrogen peroxide content in the crop and also, with the high adhesion of bacteria to the aluminium alloy surface.

 

When the aluminum alloy is coated with a polymeric film, synthesized by the mixing of Tetraethoxysilane (TEOS) and trietoxioctilsilano (TEOCS), surface examinations in the confocal microscope reveal that the polymer possess antibacterial ability against the bacteria.  In addition, the electrochemical experiments show that the coating inhibits the microbiologically influenced corrosion on the alloy in 0.1 M NaCl. The nature of the antibacterial ability resides mainly in the hydrophobic characteristic of polymers and  pH changes at the polymer-electrolyte interface.