title: Understanding the microbial corrosion from the first principle at the atomistic scale
Creators: name: Asif, Mohammad
Publisher: name: Memorial University of Newfoundland
publisherIdentifier: https://ror.org/04haebc03
publisherIdentifierScheme: ROR
Year: 2025

description: The corrosion of the metals (Fe, Ni, and Zn) is influenced by various factors, such as the presence of microbes on the surface, type of surface, and environmental conditions; however, the mechanisms controlling this impact are poorly understood. The corrosion-causing components can be sulfur, hydrogen, H₂S and SO₄ over the metal surfaces. The propagation of the corrosion could be minimized either by allying or applying inhibitors on the surface. A molecular modeling approach using Density Functional Theory (DFT) could be a useful tool to understand such a complex transformation occurring in the environment. Microbes can eliminate protons from the biofilm or consume electrons from the metal surface. This electron removal activity is modeled as an electric field. A positive/negative electric field is proposed for electron donation/acceptance to mimic the microbes over the surface. The change in adsorption energy due to the electric field for the corrosive species and inhibitors is studied in this thesis. It has been observed that the adsorption energy of the sulfur, hydrogen, and SO₄, on the Fe (110), Fe (100), and Fe (310) surfaces increased with the application of the electric field irrespective of the direction (negative/ positive) of the electric field. The H₂S, spontaneously dissociates over the Fe (100) surface. The molecular form of the H₂S is weakly adsorbed on the Fe (100) surface; however, the sulfur and hydrogen are strongly adsorbed over the iron surface. The addition of an allying element (Cr) improves the corrosion-resistant property of the iron. Furthermore, the hydrogen atom can diffuse into the sublayer of iron; however, doping the Cr atom into iron increases the diffusion barrier. This study shows that hydrogen diffusion into to sublayer of iron follows a tortuous path. The propagation of the corrosion could be explained by the thermochemical stability of the material. The Pourbaix diagram for the metals Zn, Ni, and alloy Zn-Ni are drawn utilizing Gibbs free energy of formation (ΔƒG). The Porbaix diagram for the Zn₁₁Ni₂,ZnNi and ZnNi₃ are compared and discussed. It was found that for the corrosion of the Zn-rich alloy, ZnNi, has a bigger area for the phase Ni²⁺,Zn²⁺, than Zn₁₁Ni₂: however, for corrosion of Ni-rich alloy ZnNi₃ has a bigger area for phase Ni²⁺,Zn²⁺ than Zn₁₁Ni₂. The adsorption of corrosion inhibitors, Sulfacetamide (SFC), Sulfamerazine (SFM), Sulfapyridine (SFP), and Sulfathiazole (SFT) increases with the application of electric field, which implies these inhibitors could be used for protection against microbial corrosion. iii The present study is valid for static conditions, however molecular dynamics could be applied to understand microbial corrosion at atomic scale. The adsorption energy of various species and Pourbaix diagram of metal/alloys are calculated at standard conditions. The present study did not discuss the corrosion due to multispecies, however most of the corrosion occurs in presence of multi species.