Effect of Bacillus and Pseudomonas biofilms on the corrosion behavior of AISI 304 stainless steel

In this research work, the corrosion tendency of stainless steel 304 caused by the Pseudomonas aeruginosa ZK and Bacillus subtilis S1X bacterial strains is investigated. The topographical features of the biofilms achieved after 14 days of incubation at 37 C-? were examined by means of scanning electron microscopy. Fourier transform infrared spectroscopic analysis of the extracellular polymeric substance was carried out to estimate the chemical composition of the biofilm. Electrochemical impedance spectroscopy and Tafel polarization test methods were applied to understand the in-situ corrosion tendency of the stainless steel 304 in the presence of P. aeruginosa ZK and B. subtilis S1X strains. Compared to the biofilm produced by the P. aeruginosa ZK, the extracellular polymeric substance in the B. subtilis S1X containing bacteria was found to be porous and non-uniform. The improved hydrophobicity and uniformity of the P. aeruginosa ZK containing biofilm retarded the corrosion of the underlying stainless steel 304 sample. Appreciably large resistance of the P. aeruginosa ZK biofilm (similar to 6.04 k omega-cm2) and hindered charge transport (11.12 k omega-cm(2)) were evident from the electrochemical impedance spectroscopy analysis. In support of these results, a large cathodic Tafel slope (0.2 V/decade) and low corrosion rate (1.69 mu A cm(-2)) were corroborated by the inhibitive properties of the P. aeruginosa ZK containing biofilm. However, the localized corrosion of the substrate in the presence of B. subtilis S1X bacteria was caused by the porosity and non-homogeneity of the extracellular polymeric substance layer. The small charge transfer resistance, high dissolution rate and pitting of the surface under B. subtilis S1X biofilm were comparable to the corrosion properties of stainless steel 304 in a controlled medium. These results highlighted the poor corrosion inhibitive properties of the B. subtilis S1X biofilm compared to the P. aeruginosa ZK bacterial strain.