Abstract
•Three propane bis-oxoindolines are found to be effective inhibitors for mild steel corrosion in 1.0 M H2SO4 solution.•The synthesized organic inhibitors acted as mixed type inhibitors with greatly anodic-type ones.•Addition of a small concentration of certain transition metal ions to the inhibitors noteworthy increased the efficiencies of the inhibitors.•The assessed thermodynamic parameters supported the physical adsorptionthe mechanism of the inhibitors.
The inhibition impacts of three synthesized propane bis-oxoindoline derivatives on the mild steel corrosion behavior in 1.0 M solution of sulfuric acid was explored using weight loss (WL), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), as well as the scanning electron microscopy (SEM) techniques. The outcomes of WL measurements displayed that the inhibition efficiencies of the tested propane bis-oxoindoline derivatives enhanced with their concentrations and reduced with rising temperature. The maximum inhibition efficiency was set to be 93 % at 288 K. PDP study revealed that the synthesizedorganic compounds act as mixed-type inhibitors with a predominant anodic type. The synergistic inhibition impact amongst the examined inhibitors and certain divalent transition metal ions followed the order: Zn2+> Co2+> Cd2+. It has been found that adsorption of bis-oxoindoline inhibitors on the steel surface are compatible with Langmuir adsorption coefficient, and the calculated thermodynamic parameters supported the physical nature of the adsorption process. The assessed activation energy for mild steel dissolution in H2SO4 was noticed to rise from 6.32 kJ mol−1 in the uninhibited medium to (24.53 – 32.59) kJ mol−1 in the presence of a 500 ppm of the examined organic compoundsconfirming strong adsorption of the inhibitor molecules, thus reducing the corrosion rates. The mechanism of corrosion of mild steel in H2SO4solution and its inhibition in the existence of the synthesized organic inhibitors were discussed. The acquired outcomes from all employed techniques were in a good accordance.