Abstract
Five selected carbazole derivatives, namely carbazole, 3,6-dibromocarbazole, 2-hydroxycarbazole, 1,2,3,4-tetrahydrocarbazole and 9-(2-ethylhexyl)carbazole-3,6-dicarboxaldehyde were investigated for their inhibitive effects on Desulfovibrio vulgaris (D. vulgaris) induced corrosion of mild steel and in 1 M HCl medium using weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The carbazole derivatives were found to be mixed type inhibitors with predominantly cathodic inhibitive effects for mild steel in 1 M HCl. Surface morphology results showed the compounds formed adsorbed film on mild steel surface in both aqueous acid and sulphate reducing bacteria (SRB) media. Quantum chemical calculations were used to provide molecular based explanations for the inhibitive effects of the compounds. The interactions of the molecules with mild steel surface was simulated based on molecular dynamic simulations approach using Fe(110) crystal surface as representative metallic surface.
Highlights
Mild steel is a widely used alloy of iron with various industrial applications
Five carbazole derivatives were investigated and their corrosion inhibition potentials for mild steel corrosion in microbial environment and 1 M HCl solution were evaluated
Surface morphology studies using the scanning electron microscope (SEM) and energy dispersive X-ray (EDX) equipment were conducted to ascertain that the studied CZs protect the steel surface againstcorrosion in the studied media
Summary
Where i°corr and icorr are corrosion current densities in the absence and presence of inhibitors respectively. The sterilized mild steel coupons were exposed to D. vulgaris for a period of 9 days, after which they were retrieved, rinsed in distilled water, wire brushed, and immersed in Clark’s reagent (1000 mL, 12.1 M HCl, 20 g antimony trioxide, and 50 g tin chloride) for 30 seconds to remove surface oxides, biofilm and other corrosion product. Where CR is the corrosion rate (g.cm−2.d−1); ΔW is the average weight loss (g) of mild steel coupons; A is the surface area (cm2) and T is the duration of immersion in days. For corrosion tests in acidic medium, mild steel specimens with freshly pre-treated surface as described above were immersed in 1 M HCl in the absence and presence of 100 ppm of the studied CZs. Thereafter, the specimens were removed, washed with distilled water, dried and utilized for surface electron microscopy (SEM) and energy dispersive x-ray (EDX) analyses. Ultra-fine convergence criteria was used for all optimization and simulation jobs, while the temperature was ramped down from 1 × 105 K to 100 K as the simulations went through 10 cycles at 100,000 steps per cycle
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